Extensions for Distributed Authoring and Versioning on the World Wide Web -- WEBDAV

WEBDAV Working Group                     Y. Y. Goland, Microsoft
INTERNET-DRAFT                 E. J. Whitehead, Jr., U.C. Irvine
<draft-ietf-webdav-protocol-03>               A. Faizi, Netscape
                                             S. R Carter, Novell
                                               D. Jensen, Novell
Expires April 6, 1998                         September 29, 1997



This HTML version was converted from plaintext ASCII to HTML by Jim Davis. Apologies for any errors inserted in the process.

Status of this Memo

This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.

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Distribution of this document is unlimited. Please send comments to the Distributed Authoring and Versioning (WEBDAV) working group at <w3c-dist-auth@w3.org>, which may be joined by sending a message with subject "subscribe" to <w3c-dist-auth-request@w3.org>.

Discussions of the WEBDAV working group are archived at <URL:http://www.w3.org/pub/WWW/Archives/Public/w3c-dist-auth>.

Abstract

This Document specifies a set of methods and content-types ancillary to HTTP/1.1 for the management of resource properties, simple name space manipulation, simple resource locking (collision avoidance) and resource version control.

                        Table of Contents
Abstract
1    Terminology
2    Data Model and Methods for DAV Properties
     2.1  Introduction
          2.1.1 The DAV Property
          2.1.2 Existing Metadata Proposals
          2.1.3 Properties and HTTP Headers
     2.2  A Property Model for HTTP Resources
          2.2.1 Overview
          2.2.2 Property Namespace
     2.3  Schemas
          2.3.1 PropSchema XML Element
          2.3.2 DTD XML Element
          2.3.3 DefinedProps XML Element
          2.3.4 PropEntries XML Element
          2.3.5 Live XML Element
     2.4  DAV Schema
          2.4.1 DAV Property
          2.4.2 Level XML Element
          2.4.3 Prop XML element
          2.4.4 PropLoc XML Attribute
          2.4.5 Example
     2.5  Property Identifiers
          2.5.1 Problem Definition
     2.6  Link XML Element
          2.6.1 Problem Description
          2.6.2 Solution Requirements
          2.6.3 Link XML Element
          2.6.4 Src XML Element
          2.6.5 Dst XML Element
          2.6.6 Example
     2.7  Multi-Status Response
          2.7.1 Problem Definition
          2.7.2 Solution Requirements
          2.7.3 Multi-Status Response
     2.8  Properties and Methods
          2.8.1 DELETE
          2.8.2 GET
          2.8.3 PROPPATCH
          2.8.4 PUT
          2.8.5 PROPFIND
3    A Proposal for Collections of Web Resources and Name Space
Operations
     3.1  Observations on the HTTP Object Model
          3.1.1 Collection Resources
          3.1.2 Creation and Retrieval of Collection Resources
          3.1.3 Source Resources and Output Resources
     3.2  MKCOL Method
          3.2.1 Problem Description
          3.2.2 Solution Requirements
          3.2.3 Request
          3.2.4 Response
          3.2.5 Example
     3.3  Standard DAV Properties
          3.3.1 IsCollection Property
          3.3.2 DisplayName Property
          3.3.3 CreationDate Property
          3.3.4 GETentity Property
          3.3.5 INDEXentity Property
          3.3.6 Content-Type XML Element
          3.3.7 Content-Length XML Element
          3.3.8 Content-Language XML Element
          3.3.9 Last-Modified XML Element
          3.3.10 Etag XML Element
     3.4  INDEX Method
          3.4.1 Problem Description
          3.4.2 Solution Requirements
          3.4.3 The Request
          3.4.4 The Response
          3.4.5 ResInfo XML Element
          3.4.6 Members XML Element
          3.4.7 Href XML Element
          3.4.8 Example
     3.5  Behavior of RFC 2068 Methods on Collections
          3.5.1 GET, HEAD for Collections
          3.5.2 POST for Collections
          3.5.3 PUT for Collections
          3.5.4 DELETE for Collections
          3.5.5 DELETE Method for Non-Collection Resources
     3.6  COPY Method
          3.6.1 Problem Description
          3.6.2 Solution Requirements
          3.6.3 The Request
          3.6.4 The Response
          3.6.5 Examples
     3.7  MOVE Method
          3.7.1 Problem Description
          3.7.2 Solution Requirements
          3.7.3 The Request
          3.7.4 The Response
          3.7.5 Examples
     3.8  ADDREF Method
          3.8.1 Problem Definition
          3.8.2 Solution Requirements
          3.8.3 The Request
          3.8.4 Example
     3.9  DELREF Method
          3.9.1 Problem Definition
          3.9.2 Solution Requirements
          3.9.3 The Request
          3.9.4 Example
     3.10 PATCH Method
          3.10.1 Problem Definition
          3.10.2 Solution Requirements
          3.10.3 The Request
          3.10.4 text/xml elements for PATCH
          3.10.5 The Response
          3.10.6 Examples
     3.11 Headers
          3.11.1 Destination Header
          3.11.2 Enforce-Live-Properties Header
          3.11.3 Overwrite Header
          3.11.4 Destroy Header
          3.11.5 Collection-Member Header
     3.12 Links
          3.12.1 Source Link Property Type
4    State Tokens
     4.1  Overview
          4.1.1 Problem Description
          4.1.2 Solution Requirements
     4.2  State Token Syntax
     4.3  State Token Conditional Headers
          4.3.1 If-State-Match
          4.3.2 If-None-State-Match
     4.4  State Token Header
     4.5  E-Tags
5    Locking
     5.1  Problem Description - Overview
          5.1.1 Exclusive Vs. Shared Locks
          5.1.2 Required Support
     5.2  LOCK Method
          5.2.1 Operation
          5.2.2 Effect of Locks on Properties and Containers
          5.2.3 Locking Replicated Resources
          5.2.4 Interaction with other Methods
          5.2.5 Lock Compatibility Table
          5.2.6 Status Codes
          5.2.7 Example
          5.2.8 Lock-Info Request Header
          5.2.9 Owner Request Header
          5.2.10 Time-Out Header
          5.2.11 State-Token Header
     5.3  Write Lock
     5.4  Lock Tokens
          5.4.1 Problem Description
          5.4.2 Proposed Solution
          5.4.3 Lock Token Definition
     5.5  UNLOCK Method
          5.5.1 Problem Definition
          5.5.2 Example
     5.6  Discovery Mechanisms
          5.6.1 Lock Type Discovery
          5.6.2 Active Lock Discovery
6    Version Control
7    Internationalization Support
8    Security Considerations

9    Acknowledgements
10   References
11   Authors' Addresses

1 Terminology

Collection - A resource that contains member resources.

Member Resource - a resource referred to by a collection. There are two types of member resources: external and internal.

Internal Member Resource - the name given to a member resource of a collection whose URI is relative to the URI of the collection.

External Member Resource - a member resource with an absolute URI that is not relative to its parentís URI.

Properties - A set of name/value pairs that contain descriptive information about a resource.

Live Properties - Properties whose semantics and syntax are enforced by the server. For example, a live "read-only" property that is enforced by the server would disallow PUTs to the associated resource.

Dead properties - Properties whose semantics and syntax are not enforced by the server. A dead "read-only" property would not be enforced by the server and thus would not be used by the server as a reason to disallow a PUT on the associated resource.

2 Data Model and Methods for DAV Properties

2.1 Introduction

2.1.1 The DAV Property

Properties are pieces of data that describe the state of a resource. Properties are data about data. The term property is used within this specification to disambiguate the concept from the overloaded terms "metadata" and "attribute". Properties are used within distributed authoring environments to provide for efficient discovery and management of resources. For example, a 'subject' property might allow for the indexing of all resources by their subject, and an 'author' property might allow for the discovery of what authors have written which documents.

2.1.2 Existing Metadata Proposals

Properties have a long played an essential role in the maintenance of large document repositories, and many current proposals contain some notion of a property. These include PICS [Miller et al., 1996], PICS-NG, the Rel/Rev draft [Maloney, 1996], Web Collections, XML [Bray, Sperberg-McQueen, 1997], several proposals on representing relationships within HTML, digital signature manifests (DCMF), and a position paper on Web metadata architecture [Berners-Lee, 1997].

Some proposals come from a digital library perspective. These include the Dublin Core [Weibel et al., 1995] metadata set and the Warwick Framework [Lagoze, 1996], a container architecture for different metadata schemas. The literature includes many examples of metadata, including MARC [MARC, 1994], a bibliographic metadata format, RFC 1807 [Lasher, Cohen, 1995], a technical report bibliographic format employed by the Dienst system, and the proceedings from the first IEEE Metadata conference describe many community-specific metadata sets.

Participants of the 1996 Metadata II Workshop in Warwick, UK [Lagoze, 1996], noted that, "new metadata sets will develop as the networked infrastructure matures" and "different communities will propose, design, and be responsible for different types of metadata." These observations can be corroborated by noting that many community-specific sets of metadata already exist, and there is significant motivation for the development of new forms of metadata as many communities increasingly make their data available in digital form, requiring a metadata format to assist data location and cataloging.

2.1.3 Properties and HTTP Headers

Properties already exist, in a limited sense, within HTTP through the use of message headers. However, in distributed authoring environments a relatively large number of properties are needed to describe the state of a resource, and setting/returning them all through HTTP headers is inefficient. Thus a mechanism is needed which allows a principal to identify a set of properties in which the principal is interested and to then set or retrieve just those properties.

2.2 A Property Model for HTTP Resources

2.2.1 Overview

The DAV property model is based on name/value doubles. The name of a property identifies the property's syntax and semantics, and provides an address with which to refer to a property. The name and value of a property is expressed as a well-formed XML element, where the name of the property is the name of the XML element, and the value of the property MUST be either blank, or a well-formed XML element value.

2.2.2 Property Namespace

2.2.2.1 Problem Definition

The requirement is to be able to associate a value with a property name on a resource and to be able to directly address that value.

2.2.2.2 Solution Requirement

Ideally a property namespace should work well with extant property implementations as well as database systems. The DAV property namespace has been specified with the following two facts in mind:
  • Namespaces associated with flat file systems are ubiquitous.
  • The majority of databases use a fixed schema mechanism. The last point makes efficient implementation of hierarchical properties difficult. Specifically, each property has a random set of children; the best a relational database can do is provide a table with name and value, where the value is a series of indexes into other tables and each index represents a specific value. However most RDBS do not provide for table pointers, only index values. Such a system would have to be jury-rigged to handle table pointers. In addition, indexing systems are optimized for a small set of relatively large tables; hierarchical property systems tend toward many properties, each with different numbers and types of children, thus potentially requiring a table for each child.

    It would seem best to implement a flat property namespace, inducing a natural isomorphism between DAV and most native file systems. Adopting such a model will not restrict RDBS from taking full advantage of their search facilities.

    However, it seems that future trends might be toward hierarchical properties. Therefore, DAV requirements [Slein et al.] stipulate that the design of the flat property system MUST be such that it will be possible to add true hierarchical properties later without breaking downlevel clients. Specifically, a flat client MUST be able to speak to a hierarchical server and a hierarchical client MUST be able to speak to a flat server. Worst case either way MUST be that the request fails.

    2.2.2.3 Property Names

    A property name identifies both the syntax and semantics of the property's value. It is critical that property names do not collide, e.g., two principals defining the same property name with two different meanings.

    The URI framework provides a mechanism to prevent namespace collision and for varying degrees of administrative control. Rather than reinvent these desirable features, DAV properties make use of them by requiring that all DAV property names MUST be URIs. Since a property is also an XML element, the name of the XML element is a URI.

    The property namespace is flat, that is, it is not possible to string together a series of property names in order to refer to a hierarchy of properties. Thus it is possible to refer to a property B but not a property A/B, where is also a property defined on the resource.

    Finally, it is not possible to define the same property twice as this would cause a collision in the resource's property namespace.

    2.3 Schemas

    A schema is a group of property names and XML elements.

    Schema discovery is used to determine if a system supports a group of properties or XML elements. A property does not necessarily contain sufficient information to identify any schema(s) to which it may belong.

    As with property names, schemas MUST use URIs as their names.

    A resource declares its support for a schema by defining a property whose name is the same as the schema's. The property SHOULD contain the PropSchema XML element.

    2.3.1 PropSchema XML Element

    Name: http://www.ietf.org/standards/dav/PropSchema
    Purpose: To provide information about properties
    Schema: http://www.ietf.org/standards/dav/
    Parent: Any
    Values: [DTD] [DefinedProps]
    Description:This property contains the definition of the schema. This definition consists of two parts. A DTD element that contains a DTD that declares all XML elements and DefinedProps that defines any properties associated with the schema. As with all XML it is possible to add extra XML elements. Therefore schemas may define extra XML elements which are to be included with their values.

    2.3.2 DTD XML Element

    Name: http://www.ietf.org/standards/dav/DTD
    Purpose: To contain the DTD for XML elements associated with the schema.
    Schema: http://www.ietf.org/standards/dav/
    Parent: Any
    Values: XML Declaration statements

    2.3.3 DefinedProps XML Element

    Name: http://www.ietf.org/standards/dav/DefinedProps
    Purpose: To contain a list of properties defined by the schema.
    Schema: http://www.ietf.org/standards/dav/
    Parent: Any
    Values: 1*PropEntries

    2.3.4 PropEntries XML Element

    Name: http://www.ietf.org/standards/dav/PropEntries
    Purpose: To contain the name of a defined property, the DTD of its value, and its live/dead status.
    Schema: http://www.ietf.org/standards/dav/
    Parent: DefinedProps
    Values: Prop [DTD] [Live]
    Description:Prop contains the name of the property. The DTD contains the DTD of the property's value. Live, if defined, indicates that the property has semantics and syntax that are enforced by the server.

    2.3.5 Live XML Element

    Name: http://www.ietf.org/standards/dav/Live
    Purpose: If present this indicates the server MUST enforce the syntax and semantics of the property.
    Schema: http://www.ietf.org/standards/dav/
    Parent: PropEntries

    2.4 DAV Schema

    The DAV Schema is specified as http://www.ietf.org/standards/dav/. This schema is used to indicate support for
  • properties that may be defined on a resource and
  • XML elements that may be returned in responses.

    2.4.1 DAV Property


    Name: http://www.ietf.org/standards/dav
    Purpose: Defines support for the DAV schema and protocol.
    Schema: http://www.ietf.org/standards/dav/
    Values: PropSchema Level
    Description:This property indicates that the resource supports the DAV schema and protocol to the level indicated. THE VALUE IN PROPSCHEMA IS TBD, WE NEED TO PROVIDE IT IN AN APPENDIX.

    2.4.2 Level XML Element


    Name: http://www.ietf.org/standards/dav/level
    Purpose: To indicate the level of DAV compliance the resource meets.
    Schema: http://www.ietf.org/standards/dav/
    Parent: DAV
    Values: "1" | "2" | "3"
    Description:A value of 1 for level indicates that the resource supports the property and namespace sections of the DAV specification. Level 2 indicates that the resource supports level 1 and the lock section of the specification, with a minimum locking capability of the write lock. Level 3 indicates support for levels 1 and 2 as well as support for the versioning section of the DAV specification.

    2.4.3 Prop XML element


    Name: http://www.ietf.org/standards/dav/prop
    Purpose: Contains properties related to a resource.
    Schema: http://www.ietf.org/standards/dav/
    Parent: Any
    Values: XML Elements
    Description:The Prop XML element is a generic container for properties defined on resources. All elements inside Prop MUST define properties related to the resource. No other elements may be used inside of a Prop element.

    2.4.4 PropLoc XML Attribute


    Name: http://www.ietf.org/standards/dav/PropLoc
    Purpose: To specify the location of the associated property.
    Schema: http://www.ietf.org/standards/dav/
    Values: URL
    Description:This attribute is used with elements inside of Props contained in responses to specify the URL of the property on the associated resource. The PropLoc attribute MUST NOT be used in requests.

    2.4.5 Example

    <?XML:Namespace href="http://www.ietf.org/standards/dav/" AS="D"/>
    <?XML:Namespace href="AIIM:Dublin:" AS="A"/>
    <D:Prop>
         <A:Author
             D:PropLoc="http://www.foo.com/resource/props/Author">
              Larry Masinter
         </A:Author>
    </D:Prop>
    

    The previous specifies that the property author exists on some unspecified resource and that the property can be directly referenced at http://www.foo.com/resource/props/Author. The resource upon which the property is defined must be determined from context.

    2.5 Property Identifiers

    2.5.1 Problem Definition

    DAV properties are resources and thus may have a URI where the value of an instance of the property may be retrieved. This URI is separate from the URI name of the property, which identifies the syntax and semantics of the property, but which does not give information on how to access the value of an instance of the property.

    A server is free to assign whatever URI it chooses to identify an instance of a property defined on a resource. In fact, a server is free not to reveal the URI of an instance of a particular resource and instead require that the client access the property through PROPFIND and PROPPATCH. However, many servers will want to allow clients to directly manipulate properties. On these servers, a client can discover the URI of an instance of a property by performing a PROPFIND and examining the PropLoc attribute, if returned, of each property.

    2.6 Link XML Element

    2.6.1 Problem Description

    A mechanism is needed to associate resources with other resources. These associations, known as links, consist of three values, a type describing the nature of the association, the source of the link, and the destination of the link. In the case of annotation, neither the source nor the destination of a link need be the resource upon which the link is recorded.

    2.6.2 Solution Requirements

    The association mechanism MUST make use of the DAV property mechanism in order to make the existence of the associations searchable.

    2.6.3 Link XML Element


    Name: http://www.ietf.org/standards/dav/link
    Purpose: To identify a property as a link and to contain the source and destination of that link.
    Schema: http://www.ietf.org/standards/dav/
    Values: 1*Src 1*Dst
    Description:Link is used to provide the sources and destinations of a link. The type of the property containing the Link XML element provides the type of the link. Link is a multi-valued element, so multiple Links may be used together to indicate multiple links with the same type.

    2.6.4 Src XML Element


    Name: http://www.ietf.org/standards/dav/src
    Purpose: To indicate the source of a link.
    Schema: http://www.ietf.org/standards/dav/
    Parent: http://www.ietf.org/standards/dav/link
    Values: URI

    2.6.5 Dst XML Element


    Name: http://www.ietf.org/standards/dav/Dst
    Purpose: To indicate the destination of a link
    Schema: http://www.ietf.org/standards/dav/
    Parent: http://www.ietf.org/standards/dav/link
    Values: URI

    2.6.6 Example

    <?XML:Namespace
         href = "http://www.ietf.org/standards/dav/" AS = "D"/>
    <?XML:Namespace
         href = "http://www.foocorp.com/Project/" AS = "F"/>
    <D:Prop>
         <Source>
              <Link>
                   <F:ProjFiles>Source</F:ProjFiles>
                   <src>http://foo.bar/program</src>
                   <dst>http://foo.bar/src/main.c</dst>
              </Link>
              <Link>
                   <F:ProjFiles>Library</F:ProjFiles>
                   <src>http://foo.bar/program</src>
                   <dst>http://foo.bar/src/main.lib</dst>
              </Link>
              <Link>
                   <F:ProjFiles>Makefile</F:ProjFiles>
                   <src>http://foo.bar/program</src>
                   <dst>http://foo.bar/src/makefile</dst>
         <Link>
         </Source>
    </D:Prop>
    

    In this example the resource http://foo.bar/program has a source property defined which contains three links. Each link contains three elements, two of which, src and dst, are part of the DAV schema defined in this document, and one which is defined by the schema http://www.foocorp.com/project/ (Source, Library, and Makefile). A client which only implements the elements in the DAV spec will not understand the foocorp elements and will ignore them, thus seeing the expected source and destination links. An enhanced client may know about the foocorp elements and be able to present the user with additional information about the links.

    2.7 Multi-Status Response

    2.7.1 Problem Definition

    Some methods effect more than one resource. The effect of the method on each of the scoped resources may be different, as such a return format that can specify the effect of the method on each resource is needed.

    2.7.2 Solution Requirements

    The solution must:
  • communicate the status code and reason
  • give the URI of the resource on which the method was invoked
  • be consistent with other return body formats

    2.7.3 Multi-Status Response

    The default multi-status response body is an text/xml HTTP entity that contains a single XML element called multiresponse, which contains a set of XML elements called response, one for each 200, 300, 400, and 500 series status code generated during the method invocation. 100 series status codes MUST NOT be recorded in a response XML element.

    2.7.3.1 MultiResponse


    Name: http://www.ietf.org/standards/dav/multiresponse
    Purpose: Contains multiple response messages.
    Schema: http://www.ietf.org/standards/dav/
    Parent: Any
    Value: 1*Response [ResponseDescription]
    Description:The ResponseDescription at the top level is used to provide a general message describing the over arching nature of the response. If this value is available an application MAY use it instead of presenting the individual response descriptions contain within the responses.

    2.7.3.2 Response


    Name: http://www.ietf.org/standards/dav/response
    Purpose: Holds a single response
    Schema: http://www.ietf.org/standards/dav/
    Parent: Any
    Value: (Prop | HREF) Status [ResponseDescription]
    Description: Prop MUST contain one or more empty XML elements representing the name of properties. Multiple properties may be included if the same response applies to them all. If HREF is used then the response refers to a problem with the referenced resource, not a property.

    2.7.3.3 Status


    Name: http://www.ietf.org/standards/dav/status
    Purpose: Holds a single HTTP status-line
    Schema: http://www.ietf.org/standards/dav/
    Parent: Response
    Value: status-line ;status-line defined in [Fielding et al., 1997]

    2.7.3.4 ResponseDescription


    Name: http://www.ietf.org/standards/dav/ResponseDescription
    Purpose: Contains a message that can be displayed to the user explaining the nature of the response.
    Schema: http://www.ietf.org/standards/dav/
    Parent: Multiresponse and/or Response
    Value: Any
    Description: This XML element provides information suitable to be presented to a user.

    2.8 Properties and Methods

    2.8.1 DELETE

    As properties are resources, the deletion of a property causes the same result as the deletion of any resource. It is worth pointing out that the deletion of a property effects both direct manipulation, that is by the property's URL, as well as indirect discovery and manipulation, that is PROPPATCH and PROPFIND.

    2.8.2 GET

    A GET with a Request-URI that identifies a property returns the name and value of that property. Accept types may be used to specify the format of the return value, but all DAV compliant servers MUST at minimum support a return type of text/xml. If text/xml is used as the response format then it MUST return the name and value of the property using the Prop XML element.

    2.8.2.1 Example

    The following example assumes that the property's URL, originally generated by the server, was discovered by examining the proploc XML attribute returned on a result from a FINDPROP.
    GET /bar.html;prop=z39.50_authors HTTP/1.1
    Host: foo.com
    
    HTTP/1.1 200 OK
    Content-Type: text/xml
    Content-Length: xxxx
    E-tag: "1234"
    Last-Modified: xxxx
    
    <?XML:Namespace
         href = "http://www.ietf.org/standards/dav/" AS = "D"/>
    <?XML:Namespace
         href = "http://www.w3.com/standards/z39.50/"AS = "Z"/>
    <D:prop>
         <Z:Authors>
              <Z:Author>Jane Doe</Z:Author>
              <Z:Author>Joe Doe</Z:Author>
               <Z:Author>Lots o'Doe</Z:Author>
         </Z:Authors>
    </D:prop>
    

    2.8.3 PROPPATCH

    The PROPPATCH method processes instructions specified in the request body to create and/or remove properties defined on the resource identified by Request-URI.

    All DAV compliant servers MUST process instructions which are specified using the PropertyUpdate, Create, and Remove XML elements of the DAV schema. The request message body MUST contain at least one PropertyUpdate XML element. Instruction processing MUST occur in the order instructions are received (i.e., from top to bottom), and MUST be performed atomically.

    2.8.3.1 PropertyUpdate XML element


    Name: http://www.ietf.org/standards/dav/PropertyUpdate
    Purpose: To contain a request to alter the properties on a resource.
    Schema: http://www.ietf.org/standards/dav/
    Parent: Any
    Values: *(Create | Remove)
    Description:This XML element is a container for the information required to modify the properties on the resource. This XML element is multi-valued.

    2.8.3.2 Create XML element


    Name: http://www.ietf.org/standards/dav/create
    Purpose: To create the DAV properties specified inside the Create XML element.
    Schema: http://www.ietf.org/standards/dav/
    Parent: http://www.ietf.org/standards/dav/PropertyUpdate
    Values: Prop
    Description:This XML element MUST contain only a Prop XML element. The elements contained by Prop specify the name and value of properties that are created on Request-URI. If a property already exists then its value is replaced. The Prop XML element MUST NOT contain a PropLoc XML attribute.

    2.8.3.3 Remove XML element


    Name: http://www.ietf.org/standards/dav/remove
    Purpose: To remove the DAV properties specified inside the Remove XML element.
    Schema: http://www.ietf.org/standards/dav/
    Parent: http://www.ietf.org/standards/dav/PropertyUpdate
    Values: Prop
    Description:Remove specifies that the properties specified in Prop should be removed. Specifying the removal of a property that does not exist is not an error. All the elements in Prop MUST be empty, as only the names of properties to be removed are required.

    2.8.3.4 Response

    The response MUST have a response body that contains a multiresponse identifying the results for each property.

    2.8.3.5 Response Codes

  • 200 OK - The command succeeded. As there can be a mixture of Create and Removes in a body, a 201 Create seems inappropriate.
  • 403 Forbidden - The client, for reasons the server chooses not to specify, can not alter one of the properties.
  • 405 Conflict - The client has provided a value whose semantics are not appropriate for the property. This includes trying to set read only properties.
  • 413 Request Entity Too Long - If a particular property is too long to be recorded then a composite XML error will be returned indicating the offending property.
  • 417 Insufficient Space on Resource - The resource does not have sufficient space to record the state of the resource after the execution of this method.
  • 418 Atomicity Failure - The command was not executed because of an atomicity failure elsewhere the caused the entire command to be aborted.

    2.8.3.6 Example

    PROPPATCH /bar.html HTTP/1.1
    Host: www.foo.com
    Content-Type: text/xml
    Content-Length: xxxx
    
    <?XML:Namespace
         href = "http://www.ietf.org/standards/dav/" AS = "D"/>
    <?XML:Namespace
         href = "http://www.w3.com/standards/z39.50/" AS = "Z"/>
    <D:PropertyUpdate>
         <Create>
              <prop>
                   <Z:authors>
                        <Z:Author>Jim Whitehead</Z:Author>
                        <Z:Author>Roy Fielding</Z:Author>
                   </Z:authors>
              </Prop>
         </Create>
         <Remove>
              <prop><Z:Copyright-Owner/></prop>
         </Remove>
    </D:PropertyUpdate>
    
    HTTP/1.1 405 Conflict
    Content-Type: text/xml
    Content-Length: xxxxx
    
    <?XML:Namespace
         href="http://www.ietf.org/standards/dav/" AS = "D"/>
    <?XML:Namespace
         href="http://www.w3.com/standards/z39.50/" AS = "Z"/>
    <D:MultiResponse>
         <ResponseDescription> Copyright Owner can not be deleted or
    altered.</ResponseDescription>
         <Response>
              <Prop><Z:authors/></Prop>
              <Status>HTTP/1.1 418 Atomicity Failure</Status>
         </Response>
         <Response>
              <Prop><Z:Copyright-Owner/></Prop>
              <Status>HTTP/1.1 405 Conflict</Status>
         </Response>
    </D:MultiResponse>
    

    2.8.4 PUT

    A PUT is specified in order to control what is returned by a GET. However a GET on a property always returns a predefined property containment format. Therefore PUT can not be used if the Request-URI refers to a property.

    2.8.5 PROPFIND

    The PROPFIND method retrieves properties defined on Request-URI. The request message body is an XML document that MUST contain only one PropFind XML element, which specifies the type of property find action to be performed. The XML element contained by PropFind specifies the type of action to be performed: retrieve all property names and values (AllProp), retrieve only specified property names and values (Prop), or retrieve only a list of all property names (Propname). When a Prop XML element is present, it specifies a list of the names of properties whose name and value are to be returned. The Prop element, when used within a FINDPROP request body MUST be empty.

    The response is a text/xml message body that contains a MultiResponse XML element which describes the results of the attempts to retrieve the various properties. If a property was successfully retrieved then its value MUST be returned in the prop XML element. In the case of Allprop and Findprop, if a principal does not have the right to know if a particular property exists, an error MUST NOT be returned. The results of this method SHOULD NOT be cached.

    2.8.5.1 Propfind XML element


    Name: http://www.ietf.org/standards/dav/Propfind
    Purpose: To specify the set of matching properties
    Schema: http://www.ietf.org/standards/dav/
    Parent: Any
    Values: (Prop | Allprop | Propname)
    Description: Propfind is a container element for the exact specification of a PROPFIND request.

    2.8.5.2 Allprop


    Name: http://www.ietf.org/standards/dav/Allprop
    Purpose: To specify that all properties are to be returned
    Schema: http://www.ietf.org/standards/dav/
    Parent: Propfind
    Description: Its presence in a PROPFIND request specifies the name and value of all properties defined on the resource MUST be returned.

    2.8.5.3 Propname


    Name: http://www.ietf.org/standards/dav/Propname
    Purpose: To specify that the names of all properties defined on the resource are to be returned.
    Schema: http://www.ietf.org/standards/dav/
    Parent: Propfind
    Description: Its presence in a PROPFIND request specifies the name of all properties defined on the resource MUST be returned.

    2.8.5.4 PropFindResult XML element


    Name: http://www.ietf.org/standards/dav/PropFindResult
    Purpose: To contain the results of a SEARCH request
    Schema: http://www.ietf.org/standards/dav/
    Parent: Any
    Values: Prop

    2.8.5.5 Example 1 - Prop

    PROPFIND  /container/ HTTP/1.1
    Host: www.foo.bar
    Content-Length: xxxx
    Content-Type: text/xml
    
    <?XML:Namespace href =
         "http://www.ietf.org/standards/dav/" AS = "G"/>
    <?XML:Namespace href =
         "http://www.foo.bar/boxschema/" AS = "B"/>
    <G:PROPFIND>
         <prop>
              <B:bigbox>
              <B:author>
              <B:DingALing>
              <B:Random>
         </prop>
    </G:PROPFIND>
    
    HTTP/1.1 207 Partial Success
    Content-Type: text/xml
    Content-Length: xxxxx
    
    <?XML:Namespace
         href ="http://www.ietf.org/standards/dav/" AS = "S">
    <?XML:Namespace href = "http://www.foo.bar/boxschema" AS = R">
    <D:MultiResponse>
         <ResponseDescription> There has been an access violation
    error. </ResponseDescription>
         <Response>
              <Prop>
                   <R:bigbox D:Proploc="http://prop.com/BoxType">
                        <BoxType>Box type A</BoxType>
                   </R:bigbox>
                   <R:author D:Proploc="http://prop.com/Author">
                        <Name>J.J. Dingleheimerschmidt</Name>
                   </R:author>
              </Prop>
              <Status>HTTP/1.1 200 Success</Status>
    </Response>
         <Response>
              <Prop><R:DingALing/><R:Random/></>
              <Status>HTTP/1.1 403 Forbidden</Status>
              <ResponseDescription> The user does not have access to
    the DingALink property. </ResponseDescription>
         </Response>
    </D:MultiResponse>
    

    The result will return all properties on the container. In this case only two properties were found. The principal did not have sufficient access rights to see the third and fourth properties so an error was returned.

    2.8.5.6 Example 2 - Allprop

    PROPFIND  /container/ HTTP/1.1
    Host: www.foo.bar
    Content-Length: xxxx
    Content-Type: text/xml
    
    <?XML:Namespace href =
         "http://www.ietf.org/standards/dav/" AS = "G"/>
    <G:PROPFIND>
         <Allprop/>
    </G:PROPFIND>
    
    HTTP/1.1 200 Success
    Content-Type: text/xml
    Content-Length: xxxxx
    
    <?XML:Namespace href =
         "http://www.ietf.org/standards/dav/" As = "S">
    <?XML:Namespace href = "http://www.foo.bar/boxschema" AS = R">
    <S:MultiResponse>
         <Prop>
              <R:bigbox D:Proploc="http://prop.com/BigBox">
                   <BoxType>Box type A</BoxType>
              </R:bigbox>
              <R:author D:Proploc="http://prop.com/Author">
                   <Name>Hadrian</Name>
              </R:author>
         </Prop>
         <Status>HTTP/1.1 200 Success</Status>
    </S:MultiResponse>
    

    This particular client only had the right to see two properties, BoxType and Author. No error is returned for the remaining properties, as the client does not even have sufficient rights to know they exist. If the client did have the right to know they existed but did not have the right to see their value, a 201 Partial Success with a multiresponse, as used in the previous example, would have been returned.

    2.8.5.7 Example 3 - Propname

    PROPFIND  /container/ HTTP/1.1
    Host: www.foo.bar
    Content-Length: xxxx
    Content-Type: text/xml
    
    <?XML:Namespace
         href = "http://www.ietf.org/standards/dav/" AS = "G"/>
    <G:PROPFIND>
         <Propname/>
    </G:PROPFIND>
    
    HTTP/1.1 200 Success
    Content-Type: text/xml
    Content-Length: xxxxx
    
    <?XML:Namespace
         href = "http://www.ietf.org/standards/dav/" As = "S">
    <?XML:Namespace
         href = "http://www.foo.bar/boxschema" AS = "R">
    <S:MultiResponse>
         <Prop>
              <R:bigbox D:Proploc="http://prop.com/BigBox"/>
              <R:author D:Proploc="http://prop.com/Author"/>
              <R:DingALing/>
              <R:Random/>
         </Prop>
         <Status>HTTP/1.1 200 Success</Status>
    </S:MultiResponse>
    
    In this case only two of the properties have direct URLs available, while the other two properties can only be referenced via PROPFIND and PROPPATCH.

    3 A Proposal for Collections of Web Resources and Name Space Operations

    3.1 Observations on the HTTP Object Model

    This section provides a description of a new type of Web resource, the collection, and discusses its interactions with the HTTP URL namespace. This discussion is a prerequisite for the specification of methods that operate on collections, given later in this document.

    3.1.1 Collection Resources

    A collection is a resource whose state consists of a list of internal members, a list of external members, and a set of properties. An internal member resource MUST have a URI that is immediately relative to the base URI of the collection, that is, a relative URI in which "../" is illegal, which must begin with "./" and which MAY contain only one other "/" at the end of the URI. An external member resource MUST be an absolute URI that is not an internal URI. Any given internal or external URI MUST only belong to the collection once, i.e., multiple instances of URIs in a collection are illegal. Properties defined on collections have no special distinction, and behave exactly as do properties on non-collection resources. The purpose of a collection resource is to model collection-like objects (e.g., a filesystem directory) within a server's namespace. Once these objects have been modeled with collections, a client may perform an INDEX, add and remove external members using ADDREF and DELREF, and perform recursive operations, such as a full hierarchy copy. To support methods which operate on collections, a server SHOULD model its collection-like objects with collection resources. For example, a server which is implemented on top of a filesystem SHOULD treat all filesystem directories exposed by the server as collection resources.

    3.1.2 Creation and Retrieval of Collection Resources

    This document specifies the MKCOL method to create new collection resources, and the INDEX method to list their contents.2 In HTTP/1.1, the PUT method is defined to store the request body at the location specified by Request-URI. While a description format for a collection can readily be constructed that could be used with PUT, the implications of sending such a description to the server are undesirable. For example, if a description of a collection that omitted some existing resources were PUT to a server, this might be interpreted as a command to remove those members. This would extend PUT to perform DELETE functionality, which is undesirable since it changes the semantics of PUT, and makes it difficult to control DELETE functionality with an access control scheme based on methods. While the POST method is sufficiently open-ended that a "create a collection" POST command could be constructed, this is undesirable because it would be difficult to separate access control for collection creation from other uses of POST if they both use the same method. While it might seem desirable to have GET return a listing of the members of a collection, this is foiled by the existence of the "index.html" de-facto standard namespace redirection, in which a GET request on a collection is automatically redirected to the index.html resource. The exact definition of the behavior of GET and PUT on collections is defined later in this document.

    3.1.2.1 Example

    The structured resource http://foo/bar is created with a PUT. Bar is a multipart/related file with two members http://foo/bar/a and http://foo/bar/b. If bar were deleted then both a and b would also be deleted since they are all really just one resource. If http://foo/bar/a/c was PUT then a DELETE on http://foo/bar/a would also delete http://foo/bar/a/c as c was created with a PUT not a MKCOL. If http://foo/bar/b/d is created with a MKCOL and http://foo/bar/b/d/e was created then a DELETE on d would fail because d is a collection with an internal member. However the existence of the collection d is something of an illusion. If a DELETE was executed on http://foo/bar then everything would be deleted, even though http://foo/bar/b/d was created with a MKCOL. Thus the effect of a MKCOL within a composite resourceís namespace is felt on its children, not its ancestors. The children of d MUST be treated as members of a collection when a method is executed on d. But a method executed on b or a is treated as if there only existed a non-collection resource.

    3.1.3 Source Resources and Output Resources

    For many resources, the entity returned by GET exactly matches the persistent state of the resource, for example, a GIF file stored on a disk. For this simple case, the URL at which a resource is accessed is identical to the URL at which the source (the persistent state) of the resource is accessed. This is also the case for HTML source files that are not processed by the server prior to transmission. However, the server can sometimes process HTML resources before they are transmitted as a return entity body. For example, server-side-include directives within an HTML file instruct a server to replace the directive with another value, such as the current date. In this case, what is returned by GET (HTML plus date) differs from the persistent state of the resource (HTML plus directive). Typically there is no way to access the HTML resource containing the unprocessed directive. Sometimes the entity returned by GET is the output of a data-producing process that is described by one or more source resources (that may not even have a location in the URL namespace). A single data-producing process may dynamically generate the state of a potentially large number of output resources. An example of this is a CGI script that describes a "finger" gateway process that maps part of the namespace of a server into finger requests, such as http://www.foo.bar.org/finger_gateway/user@host. In the absence of distributed authoring capability, it is acceptable to have no mapping of source resource(s) to the URI namespace, and in fact has desirable security benefits. However, if remote editing of the source resource(s) is desired, the source resource(s) should be given a location in the URI namespace. This source location should not be one of the locations at which the generated output is retrievable, since in general it is impossible for the server to differentiate requests for source resources from requests for process output resources. There is often a many-to-many relationship between source resources and output resources. For DAV compliant servers all output resources which have a single source resource (and that source resource has a URI), the URI of the source resource SHOULD be stored in a single link on the output resource with type http://www.ietf.org/standards/dav/source. Note that by storing the source URI in links on the output resources, the burden of discovering the source is placed on the authoring client.

    3.2 MKCOL Method

    3.2.1 Problem Description

    A client must be able to create a collection.

    3.2.2 Solution Requirements

    The solution:
  • Must ensure that a collection has been made (i.e. that it responds to the INDEX method) as opposed to a non-collection resource. If a collection could not be made, it must indicate this failure to the user-agent.

    3.2.3 Request

    MKCOL creates a new collection resource at the location specified by the Request-URI. If the Request-URI exists, then MKCOL must fail. During MKCOL processing, a server MUST make the Request-URI a member of its parent collection. If no such an ancestor exists, the method MUST fail. When the MKCOL operation creates a new collection resource, all ancestors MUST already exist, or the method MUST fail with a 409 Conflict status code. For example, if a request to create collection /a/b/c/d/ is made, and neither /a/b/ nor /a/b/c/ exist, the request MUST fail.

    3.2.3.1 MKCOL Without Request Body

    When MKCOL is invoked without a request body, the newly created collection has no members.

    3.2.3.2 MKCOL With Request Body

    A MKCOL request message MAY contain a message body. The behavior of a MKCOL request when the body is present is limited to creating collections, members of a collection, bodies of members and properties on the collections or members. If the server receives a MKCOL request entity type it does not support or understand it MUST respond with a 415 (Unsupported Media Type) status code. The exact behavior of MKCOL for various request media types is undefined in this document, and will be specified in separate documents.

    3.2.4 Response

    Responses from a MKCOL request are not cacheable, since MKCOL has non-idempotent semantics.
  • 201 (Created) - The collection or structured resource was created in its entirety.
  • 403 (Forbidden) - This indicates at least one of two conditions: 1) The server does not allow the creation of collections at the given location in its namespace, and 2) The parent collection of the Request-URI exists but cannot accept members.
  • 409 (Conflict) - A collection cannot be made at the Request-URI until one or more intermediate collections have been created.
  • 415 (Unsupported Media Type)- The server does not support the request type of the body.
  • 417 (Insufficient Space on Resource) - The resource does not have sufficient space to record the state of the resource after the execution of this method.

    3.2.5 Example

    This example creates a container collection called /webdisc/xfiles/ on the server www.server.org.
         MKCOL /webdisc/xfiles/ HTTP/1.1
         Host: www.server.org
    
         HTTP/1.1 201 Created
    

    3.3 Standard DAV Properties

    The following properties are defined on DAV compliant resources. All enclosed properties are part of the DAV Schema.

    3.3.1 IsCollection Property


    Name: http://www.ietf.org/standards/dav/iscollection
    Purpose: This property contains a Boolean value that is set to "true" if the resource is a collection
    Schema: http://www.ietf.org/standards/dav/
    Value: ("true" | "false")
    Description: This property MUST be defined on all DAV compliant resources.

    3.3.2 DisplayName Property


    Name: http://www.ietf.org/standards/dav/displayname
    Purpose: A name for the resource that is suitable for presentation to a user.
    Schema: http://www.ietf.org/standards/dav/
    Value: Any valid XML character data (as defined in [Bray, Sperberg-McQueen, 1997])
    Description: This property SHOULD be defined on all DAV compliant resources. If present, the property a description of the resource that is suitable for presentation to a user.

    3.3.3 CreationDate3 Property


    Name: http://www.ietf.org/standards/dav/creationdate
    Purpose: The time and 4date the resource was created.
    Schema: http://www.ietf.org/standards/dav/
    Value: The time and date MUST be given in ISO 8601 format [ISO8601]
    Description: This property SHOULD be defined on all DAV compliant resources. If present, it contains a timestamp of the moment when the resource was created (i.e., the moment it had non-null state).

    3.3.4 GETentity Property5


    Name: http://www.ietf.org/standards/dav/GETentity
    Purpose: Contains the value of headers that are returned by a GET without Accept headers.
    Schema: http://www.ietf.org/standards/dav/
    Value: Content-Type Content-Length Content-Language Last-Modified Etag Creation-Date
    Description: This property MUST be defined on all DAV compliant resources unless GET is not supported, in which case this property MUST NOT be defined. This property MUST contain at most one instance of each element in its Value, if they are defined.

    3.3.5 INDEXentity Property


    Name: http://www.ietf.org/standards/dav/INDEXentity
    Purpose: Contains the value of headers that are returned by an INDEX.
    Schema: http://www.ietf.org/standards/dav/
    Value: Content-Type Content-Length Content-Language Last-Modified Etag Creation-Date
    Description: This property MUST be defined on all DAV compliant resources unless INDEX is not supported, in which case this property MUST NOT be defined. This property MUST contain at most one instance of each element in its Value, if they are defined.

    3.3.6 Content-Type XML Element


    Name: http://www.ietf.org/standards/dav/content-type
    Purpose: The content-type of the member resource.
    Schema: http://www.ietf.org/standards/dav/
    Parent: GETentity or INDEXentity
    Value: media-type ; defined in Section 3.7 of [Fielding et al., 1997]
    Description: If the parent of this element is GETentity, the value MUST be identical to the content-type returned by a GET on the resource without Accept headers. If the parent is INDEXentity, the value MUST be identical to the content-type returned by an INDEX on the resource. If no content-type is available, this element MUST NOT be defined.

    3.3.7 Content-Length XML Element


    Name: http://www.ietf.org/standards/dav/content-length
    Purpose: Describes the default content-length of the resource.
    Schema: http://www.ietf.org/standards/dav/
    Value: content-length ; see section 14.14 of RFC 2068
    Description: If the parent of this element is GETentity, this element MUST have a value equal to the content-length header returned by a GET on the resource without Accept headers. If the parent is INDEXentity, the value MUST be identical to the content-length returned by an INDEX on the resource. If no content-length is available, this element MUST NOT be defined.

    3.3.8 Content-Language XML Element


    Name: http://www.ietf.org/standards/dav/content-language
    Purpose: Describes the default natural language of a resource.
    Schema: http://www.ietf.org/standards/dav/
    Value: language-tag ;language-tag is defined in section 14.13 of RFC 2068
    Description: If the parent of this element is GETentity, this element MUST have a value equal to the content-language header returned by a GET on the resource without Accept headers. If the parent is INDEXentity, the value MUST be identical to the content-language header returned by an INDEX on the resource. If no content-language header is available, this element MUST NOT be defined.

    3.3.9 Last-Modified XML Element


    Name: http://www.ietf.org/standards/dav/last-modified
    Purpose: The date the resource was last modified.
    Schema: http://www.ietf.org/standards/dav/
    Parent: GETentity or INDEXentity
    Value: The date MUST be given in RFC 1123 format (rfc-1123 production, defined in section 3.3.1 of [Fielding et al., 1997]
    Description: If the parent of this element is GETentity, this element MUST have a value equal to the last-modified header returned by a GET on the resource without Accept headers. If the parent is INDEXentity, the value MUST be identical to the last-modified header returned by an INDEX on the resource. If no last-modified header is available, this element MUST NOT be defined.

    3.3.10 Etag XML Element


    Name: http://www.ietf.org/standards/dav/etag
    Purpose: The entity tag of the resource.
    Schema: http://www.ietf.org/standards/dav/
    Parent: GETentity or INDEXentity
    Value: entity-tag ; defined in Section 3.11 of [Fielding et al., 1997]
    Description: If the parent of this element is GETentity, this element MUST have a value equal to the entity-tag header returned by a GET on the resource without Accept headers. If the parent is INDEXentity, the value MUST be identical to the entity-tag header returned by an INDEX on the resource. If no entity-tag header is available, this element MUST NOT be defined.

    3.4 INDEX Method

    3.4.1 Problem Description

    A mechanism is needed to discover if a resource is a collection and if so, list its members.

    3.4.2 Solution Requirements

    The solution:
  • must allow a client to discover the members of a collection
  • must always provide a machine-readable description of the membership of a collection
  • must be leveraged as a more general mechanism to provide a list of contents for any resource which can profitably return a membership like listing.

    3.4.3 The Request

    The INDEX method returns a machine-readable representation of the membership of the resource at the Request-URI.

    For a collection, INDEX MUST return a list of its members. All WebDAV compliant resources MUST support the text/xml response entity described below. The INDEX result for a collection MAY also return a list of the members of child collections, to any depth.

    Collections that respond to an INDEX method with a text/xml entity MUST contain only one ResInfo element. This ResInfo element contains an Href element, which gives the identifier(s) of the resource, a Prop element, which gives selected properties of the resource, and a Members element, which contains a ResInfo element for each member of the collection. The Prop element MUST contain at least the following properties, if they are defined and available: DisplayName, IsCollection, CreationDate, GETentity, and INDEXentity.

    The response from INDEX is cacheable, and SHOULD be accompanied by an ETag header (see section 13.3.4 of RFC 2068). If GET and INDEX return different entities for the same resource state, they MUST return different entity tags.

    3.4.4 The Response

  • 200 (OK) - The server MUST send a machine readable response entity which describes the membership of the resource.

    3.4.5 ResInfo XML Element


    Name: http://www.ietf.org/standards/dav/resinfo
    Purpose: Describes a resource.
    Schema: http://www.ietf.org/standards/dav/
    Parent: Any
    Value: Href Prop Members
    Description: There MUST be at least one Href element. Each Href element contains a URI for the resource, which MUST be an absolute URI. There MUST be a single Prop element that contains a series of properties defined on the resource. If the resource is a collection, it MAY have at most one Members element, which describes the members of the collection.

    3.4.6 Members XML Element


    Name: http://www.ietf.org/standards/dav/members
    Purpose: Describes the membership of a collection resource.
    Schema: http://www.ietf.org/standards/dav/
    Parent: ResInfo
    Value: ResInfo
    Description: Contains zero or more ResInfo elements, which describe members of the collection.

    3.4.7 Href XML Element


    Name: http://www.ietf.org/standards/dav/href
    Purpose: To identify that the content of the element is a URI.
    Schema: http://www.ietf.org/standards/dav/
    Parent: Any
    Value: URI ; See section 3.2.1 of [Fielding et al., 1997]

    3.4.8 Example

    INDEX /user/yarong/dav_drafts/ HTTP/1.1
    Host: www.microsoft.com
    
    HTTP/1.1 200 OK
    Content-Type: text/xml
    Content-Length: xxx
    Last-Modified: Thu, 11 Sep 1997 23:45:12 GMT
    ETag: "fooyyybar"
    
    <?XML:Namespace
         href = "http://www.ietf.org/standards/dav/" as = "D"/>
    <D:ResInfo>
         <XML:Href>
              http://www.microsoft.com/user/yarong/dav_drafts/
         </XML:Href>
         <Prop>
            <DisplayName>
              WebDAV working drafts directory
            </DisplayName>
            <IsCollection>true</IsCollection>
            <CreationDate>19970418T070304Z</CreationDate>
            <GETentity>
              <Content-Type>text/html</Content-Type>
              <Content-Length>2754</Content-Length>
              <Content-Language>en</Content-Language>
              <Last-Modified>
                   Fri, 22 Aug 1997 10:11:26 GMT
              </Last-Modified>
              <Etag>"8675309"</Etag>
            </GETentity>
            <INDEXentity>
              <Content-Type>text/xml</Content-Type>
              <Content-Length>xxx</Content-Length>
              <Last-Modified>
                   Thu, 11 Sep 1997 23:45:12 GMT
              </Last-Modified>
              <Etag>"fooyyybar"</Etag>
            </INDEXentity>
         </Prop>
    
         <Members>
            <ResInfo>
              <XML:Href>
              http://www.microsoft.com/user/yarong/dav_drafts/base
              </XML:Href>
              <Prop>
                 <IsCollection
         D:PropLoc="http://www.microsoft.com/user/yarong/dav_drafts/b
         ase;props=IsCollection">
                   False
                 </IsCollection>
                 <DisplayName>
                   WebDAV Name Space Operations Draft
                 </DisplayName>
                 <Creation-Date>19970320T230525Z</Creation-Date>
                 <GETentity>
                   <Content-Type>application/msword</Content-Type>
                   <Content-Length>1400</Content-Length>
                   <Content-Language>en</Content-Language>
                   <Last-Modified>
                        Fri, 22 Aug 1997 18:22:56 GMT
                   </Last-Modified>
                   <Etag>"8675309"</Etag>
                 </GETentity>
              </Prop>
            </ResInfo>
         </Members>
    </D:ResInfo>
    

    This example shows the result of the INDEX method applied to the collection resource http://www.microsoft.com/user/yarong/dav_drafts/. It returns a response body in XML format, which gives information about the container and its sole member, http://www.microsoft.com/user/yarong/dav_drafts/base. The entry on the collection confirms that resource the INDEX was executed on is a collection. The result also contains the URI of the IsCollection property on the member resource.

    3.5 Behavior of RFC 2068 Methods on Collections

    With the introduction of the collection resource type to the HTTP object model, it is necessary to define the behavior of the existing methods (defined in RFC 2068) when invoked on a collection resource to avoid ambiguity. While some methods, such as OPTIONS and TRACE behave identically when applied to collections, GET, HEAD, POST, PUT, and DELETE require some additional explanation.

    3.5.1 GET, HEAD for Collections

    The semantics of GET are unchanged when applied to a collection, since GET is defined as, "retrieve whatever information (in the form of an entity) is identified by the Request-URI" [Fielding et al., 1997]. GET when applied to a collection MAY return the contents of an "index.html" resource, a human-readable view of the contents of the collection, or something else altogether, and hence it is possible the result of a GET on a collection will bear no correlation to the state of the collection. Similarly, since the definition of HEAD is a GET without a response message body, the semantics of HEAD are unmodified when applied to collection resources.

    3.5.2 POST for Collections

    Since by definition the actual function performed by POST is determined by the server and often depends on the particular resource, the behavior of POST when applied to collections cannot be meaningfully modified because it is largely undefined. Thus the semantics of POST are unmodified when applied to a collection.

    3.5.3 PUT for Collections

    As defined in the HTTP/1.1 specification [Fielding et al., 1997], the "PUT method requests that the enclosed entity be stored under the supplied Request-URI." Since submission of an entity representing a collection would implicitly encode creation and deletion of resources, this specification intentionally does not define a transmission format for creating a collection using PUT. Instead, the MKCOL method is defined to create collections. If a PUT is invoked on a collection resource it MUST fail. When the PUT operation creates a new non-collection resource all ancestors MUST already exist. If all ancestors do not exist, the method MUST fail with a 409 Conflict status code. For example, if resource /a/b/c/d.html is to be created and /a/b/c/ does not exist, then the request MUST fail.

    3.5.3.1 PUT for Non-Collection Resources

    A PUT performed on an existing resource replaces the GET response entity of the resource, but MUST NOT change the value of any dead properties defined on the resource. Live properties defined on the resource MAY be recomputed during PUT processing.

    3.5.4 DELETE for Collections

    When DELETE is applied to a collection without internal members the collection resource, along with its properties, and external members, MUST be deleted. A DELETE method applied to a collection resource containing internal member resources MUST fail with a 409 Conflict status code.

    3.5.5 DELETE Method for Non-Collection Resources

    If the DELETE method is issued to a non-collection resource which is an internal member of a collection, then during DELETE processing a server MUST remove the Request-URI from its parent collection. A server MAY remove the URI of a deleted resource from any collections of which the resource is an external member.

    3.6 COPY Method

    3.6.1 Problem Description

    Currently, in order to create a copy of a resource, the client must GET an entity and then PUT that entity to the desired destination. This requires (1) an entity to be transmitted to and from the server and (2) that the resource be expressible as an entity with complete fidelity. This is problematic because of the network traffic involved in making a copy, and because there is often no way to fully express a resource as an entity without a loss of fidelity.

    3.6.2 Solution Requirements

    The solution:
  • MUST allow a principal to create a copy of a resource without having to transmit the resource to and from the server.

    3.6.3 The Request

    The COPY method creates a duplicate of the source resource, given by the Request-URI, in the destination resource, given by the Destination header. The Destination header MUST be present. The exact behavior of the COPY method depends on the type of the source resource.

    3.6.3.1 COPY for HTTP/1.1 resources

    When the source resource is not a collection, and is not a property, the body of the destination resource MUST be octet-for-octet identical to the body of the source resource. Alterations to the destination resource do not modify the source resource. Alterations to the source resource do not modify the destination resource. Thus, all copies are performed "by-value". All properties on the source resource MUST be duplicated on the destination resource, subject to modifying headers, following the definition for copying properties.

    3.6.3.2 COPY for Properties

    The following section defines how properties on a resource are handled during a COPY operation. Live properties SHOULD be duplicated as identically behaving live properties at the destination resource. Since they are live properties, the server determines the syntax and semantics (hence value) of these properties. Properties named by the Enforce-Live-Properties header MUST be live on the destination resource, or the method MUST fail. If a property is not named by Enforce-Live-Properties and cannot be copied live, then its value MUST be duplicated, octet-for-octet, in an identically named, dead resource on the destination resource. If a property on the source already exists on the resource and the overwrite header is set to TRUE then the property at the destination MUST be overwritten with the property from the source. If the overwrite header is false and the previous situation exists then the COPY MUST fail with a 409 Conflict.

    3.6.3.3 COPY for Collections

    A COPY on a collection causes a collection resource to be created at the destination with the same properties, but without any members, internal or external. All properties on the source collection are copied over to the destination collection. Where there is a conflict the source properties will overwrite the destination properties. Any members at the [sic] MUST be duplicated on the destination collection, subject to modifying headers, following the definition for copying properties.

    3.6.3.4 Type Interactions

    If the destination resource identifies a property and the source resource is not a property, then the copy SHOULD fail. If the destination resource identifies a collection and the Overwrite header is "true," prior to performing the copy, the server MUST perform a DELETE operation on the collection.

    3.6.4 The Response

  • 200 (OK) The source resource was successfully copied to a pre-existing destination resource.
  • 201 (Created) The source resource was successfully copied. The copy operation resulted in the creation of a new resource.
  • 412 (Precondition Failed) This status code MUST be returned if the server was unable to maintain the liveness of the properties listed in the Enforce-Live-Properties header, or if the Overwrite header is false, and the state of the destination resource is non-null.
  • 417 (Insufficient Space on Resource) - The destination resource does not have sufficient space to record the state of the resource after the execution of this method.
  • 500 (Server Error) The resource was in such a state that it could not be copied. This may occur if the Destination header specifies a resource that is outside the namespace the resource is able to interact with.

    3.6.5 Examples

    3.6.5.1 Overwrite Example

    This example shows resource http://www.ics.uci.edu/~fielding/index.html being copied to the location http://www.ics.uci.edu/users/f/fielding/index.html. The contents of the destination resource were overwritten, if non-null.
    COPY /~fielding/index.html HTTP/1.1
    Host: www.ics.uci.edu
    Destination: http://www.ics.uci.edu/users/f/fielding/index.html
    
    HTTP/1.1 200 OK
    

    3.6.5.2 No Overwrite Example

    The following example shows the same copy operation being performed, except with the Overwrite header set to "false." A response of 412, Precondition Failed, is returned because the destination resource has a non-null state.
    COPY /~fielding/index.html HTTP/1.1
    Host: www.ics.uci.edu
    Destination: http://www.ics.uci.edu/users/f/fielding/index.html
    Overwrite: "false"
    
    HTTP/1.1 412 Precondition Failed
    

    3.7 MOVE Method

    3.7.1 Problem Description

    The move operation on a resource is the logical equivalent of a copy followed by a delete, where the actions are performed atomically. Using RFC 2068 methods only, this procedure could be performed in several steps. First, the client could issue a GET to retrieve a representation of a resource, issue a DELETE to remove the resource from the server, then use PUT to place the resource on the server with a new URI. As is the case for COPY - because of the network traffic involved in making a move, and because there is often no way to fully express a resource as an entity without a loss of fidelity - server move functionality is preferable. With a WEBDAV server, a principal may accomplish this task by issuing a COPY and then DELETE. Network load decreases, but the server load may still be significant because the server must create a duplicate resource. Were a server to know beforehand that a principal intended to perform COPY and DELETE operations in succession, it could avoid the creation of a duplicate resource.

    3.7.2 Solution Requirements

    The solution:
  • Must prevent the unneeded transfer of entity bodies from and to the server.
  • Must prevent the unneeded creation of copies by the server.

    3.7.3 The Request

    The move operation on a resource is the logical equivalent of a copy followed by a delete, where the actions are performed atomically. If a resource exists at the destination, the destination resource will be DELETEd as a side effect of the MOVE operation, subject to the restrictions of the overwrite header.

    3.7.4 The Response

  • 200 (OK) - The resource was moved. A successful response must contain the Content-Location header, set equal to the URI in source. This lets caches properly flush any cached entries for the source. Unfortunately the Content-Location header only allows a single value so it is not possible for caches unfamiliar with the MOVE method to properly clear their caches.
  • 412 (Precondition Failed) This status code MUST be returned if the server was unable to maintain the liveness of the properties listed in the Enforce-Live-Properties header, or if the Overwrite header is false, and the state of the destination resource is non- null.
  • 501 (Not Implemented) - This may occur if the Destination header specifies a resource which is outside its domain of control (e.g., stored on another server) resource and the server either refuses or is incapable of moving to an external resource.
  • 502 (Bad Gateway) - This may occur when moving to external resources and the destination server refused to accept the resource.

    3.7.5 Examples

    3.7.5.1 Overwrite Example

    This example shows resource http://www.ics.uci.edu/~fielding/index.html being moved to the location http://www.ics.uci.edu/users/f/fielding/index.html. The contents of the destination resource were overwritten, if non-null.
    MOVE /~fielding/index.html HTTP/1.1
    Host: www.ics.uci.edu
    Destination: http://www.ics.uci.edu/users/f/fielding/index.html
    
    HTTP/1.1 200 OK
    Content-Location:
    http://www.ics.uci.edu/users/f/fielding/index.html
    

    3.8 ADDREF Method

    3.8.1 Problem Definition

    There needs to be a way to add an external member to a collection.

    3.8.2 Solution Requirements

    The solution must:
  • allow access control
  • allow referencing to URIs of external members
  • not require a body

    3.8.3 The Request

    The ADDREF method adds the URI specified in the Collection-Member header as an external member to the collection specified by the Request-URI. The value in the Collection-Member header MUST be an absolute URI meeting the requirements of an external member URI. It is not an error if the URI specified in the Collection-Member header already exists as an external member of the collection, however, after processing ADDREF there MUST be only one instance of the URI in the collection. If the URI specified in the Collection-Member header already exists as an internal member of the collection, the ADDREF method MUST fail with a 412 Precondition Failed status code.

    3.8.4 Example

    ADDREF /~whitehead/dav/ HTTP/1.1
    HOST: www.ics.udi.edu
    Collection-Member: http://www.ietf.org/standards/dav/
    
    HTTP/1.1 200 OK
    

    3.9 DELREF Method

    3.9.1 Problem Definition

    There needs to be a way to remove an external member from a collection.

    3.9.2 Solution Requirements

    The solution must:
  • allow access control
  • allow referencing to URIs of external members
  • not require a body

    3.9.3 The Request

    The DELREF method removes the URI specified in the Collection-Member header from the collection specified by the Request-URI. DELREFing a URI which is not a member of the collection is not an error. DELREFing an internal member MUST fail with a 412 Precondition Failed status code.

    3.9.4 Example

    DELREF /~whitehead/dav/ HTTP/1.1
    Host: www.ics.udi.edu
    Collection-Member: http://www.ietf.org/standards/dav/
    
    HTTP/1.1 200 OK
    

    3.10 PATCH Method

    3.10.1 Problem Definition

    At present, if a principal wishes to modify a resource, they must issue a GET against the resource, modify their local copy of the resource, and then issue a PUT to place the modified resource on the server. This procedure is inefficient because the entire entity for a resource must be transmitted to and from the server in order to make even small changes. Ideally, the update entity transmitted to the server should be proportional in size to the modifications.

    3.10.2 Solution Requirements

    The solution must:
  • allow partial modification of a resource without having to transmit the entire modified resource
  • allow byte-range patching
  • allows extensions so that patches can be done beyond simple byte-range patching
  • allow ranges to be deleted, inserted, and replaced

    3.10.3 The Request

    The request entity of the PATCH method contains a list of differences between the resource identified by the Request-URI and the desired content of the resource after the PATCH action has been applied. The list of differences is in a format defined by the media type of the entity (e.g., "application/diff") and must include sufficient information to allow the server to convert the original version of the resource to the desired version. Processing performed by PATCH is atomic, hence all changes MUST be successfully executed or the method fails. PATCH MUST fail if executed on a non-existent resource; i.e. PATCH does not create a resource as a side effect. If the request appears (at least initially) to be acceptable, the server MUST transmit an interim 100 response message after receiving the empty line terminating the request headers and continue processing the request. Since the semantics of PATCH are non-idempotent, responses to this method are not cacheable. While server support for PATCH is optional, if a server does support PATCH, it MUST support at least the text/xml diff format defined below. Support for the VTML difference format [VTML] is recommended, but not required.

    3.10.4 text/xml elements for PATCH

    The resourceupdate XML element contains a set of XML sub-entities that describe modification operations. The name and meaning of these XML elements is given below. Processing of these directives MUST be performed in the order encountered within the XML document. A directive operates on the resource as modified by all previous directives (executed in sequential order). The length of the resource MAY be extended or reduced by a PATCH. The changes specified by the resourceupdate XML element MUST be executed atomically.

    3.10.4.1 ResourceUpdate


    Name: http://www.ietf.org/standards/dav/patch/resourceupdate
    Purpose: Contains an ordered set of changes to a non-collection, non-property resource.
    Schema: http://www.ietf.org/standards/dav/patch/
    Parent: Any
    Value: *(Insert | Delete | Replace)

    3.10.4.2 Insert


    Name: http://www.ietf.org/standards/dav/patch/insert
    Purpose: Insert the XML elementís contents starting at the specified octet.
    Schema: http://www.ietf.org/standards/dav/patch/
    Parent: ResourceUpdate
    Value: The insert XML element MUST contain an Octet-Range XML element that specifies an octet position within the body of a resource. A value of "end" specifies the end of the resource. The body of the insert XML element contains the octets to be inserted.

    Please note that in order to protect the white space contained in this XML element the following attribute/value MUST be included in the element: XML-SPACE = "PRESERVE".

    3.10.4.3 Delete


    Name: http://www.ietf.org/standards/dav/patch/delete
    Purpose: Removes the specified range of octets.
    Schema: http://www.ietf.org/standards/dav/patch/
    Parent: ResourceUpdate
    Value: The Delete XML element MUST contain an octet-range XML element.
    Discussion: The octets that are deleted are removed, which means the resource is collapsed and the length of the resource is decremented by the size of the octet range. It is not appropriate to replace deleted octets with zeroed-out octets, since zero is a valid octet value.

    3.10.4.4 Replace


    Name: http://www.ietf.org/standards/dav/patch/replace
    Purpose: Replaces the specified range of octets with the contents of the XML element. If the number of octets in the XML element is different from the number of octets specified, the update MUST be rejected.
    Schema: http://www.ietf.org/standards/dav/patch/
    Parent: ResourceUpdate
    Value: The Replace XML element MUST contain an octet-range XML element. The contents of the entity are the replacement octets. Please note that in order to protect the white space contained in this XML element the following attribute/value MUST be included in the element: XML-SPACE = "PRESERVE".

    3.10.4.5 Octet-Range Attribute


    Name: http://www.ietf.org/standards/dav/patch/octet-range
    Purpose: Specifies a range of octets that the enclosing property effects.
    Schema: http://www.ietf.org/standards/dav/patch/
    Parent: Insert, Delete, Replace
    Value: number ["-" (number | "end")]
    Number = 1*Digit
    Description: Octet numbering begins with 0. If the octet contains a single number then the operation is to begin at that octet and to continue for a length specified by the operation. In the case of a delete, this would mean to delete a single octet. In the case of an insert this would mean to begin the insertion at the specified octet and to continue for the length of the included value, extending the resource if necessary. In the case of replace, the replace begins at the specified octet and overwrites all that follow to the length of the included value.

    3.10.5 The Response

  • 200 (OK) - The request entity body was processed without error, resulting in an update to the state of the resource.
  • 409 (Conflict) - If the update information in the request message body does not make sense given the current state of the resource (e.g., an instruction to delete a non-existent line), this status code MAY be returned.
  • 415 (Unsupported Media Type) - The server does not support the content type of the update instructions in the request message body.
  • 416 (Unprocessable Entity) - A new status code. The server understands the content type of the request entity, but was unable to process the contained instructions.
  • 417 (Insufficient Space on Resource) - The resource does not have sufficient space to record the state of the resource after the execution of this method.

    3.10.6 Examples

    3.10.6.1 HTML file modification

    The following example shows a modification of the title and contents of the HTML resource http://www.example.org/hello.html.

    Before:

         <HTML>
         <HEAD>
         <TITLE>Hello world HTML page</TITLE>
         </HEAD>
         <BODY>
         <P>Hello, world!</P>
         </BODY>
         </HTML>
    

    PATCH Request: Response:

         PATCH hello.html HTTP/1.1
         Host: www.example.org
         Content-Type: text/xml
         Content-Length: xxx
    
                                       HTTP/1.1 100 Continue
         <?XML:Namespace href =
         "http://www.ietf.org/standards/dav/patch/" AS = "D"/>
         <D:ResourceUpdate>
              <Replace XML-SPACE = "PRESERVE"><octet-range>14</octet-range>
             &003CTITLE&003ENew Title&003C/TITLE&003E</Replace>
              <Delete><octet-range>38-50</Delete>
         <Insert XML-SPACE = "PRESERVE"><octet-range>86</>&003CP&003ENew paragraph&003C/P&003E</Insert>
         </D:ResourceUpdate>
                                       HTTP/1.1 200 OK
    

    After:

         <HTML>
         <HEAD>
         <TITLE>New Title</TITLE>
         </HEAD>
         <BODY>
         <P>Hello, world!</P>
         <P>New paragraph</P>
         </BODY>
         </HTML>
    

    3.11 Headers

    3.11.1 Destination Header

    The Destination header specifies a destination resource for methods such as COPY and MOVE, which take two URIs as parameters. Destination= "Destination" ":" URI

    3.11.2 Enforce-Live-Properties Header

    The Enforce-Live-Properties header specifies properties that MUST be "live" after they are copied (moved) to the destination resource of a copy (or move). If the value "*" is given for the header, then it designates all live properties on the source resource. If the value is "Omit" then the server MUST NOT duplicate on the destination resource any properties that are defined on the source resource. If this header is not included then the server is expected to act as defined by the default property handling behavior of the associated method.
         EnforceLiveProperties = "Enforce-Live-Properties" ":" ("*" |
         "Omit" | 1#(Property-Name))
         Property-Name = "<" URI ">"
    

    3.11.3 Overwrite Header

    The Overwrite header specifies whether the server should overwrite the state of a non-null destination resource during a COPY or MOVE. A value of "false" states that the server MUST NOT perform the COPY or MOVE operation if the state of the destination resource is non-null. By default, the value of Overwrite is "true," and a client MAY omit this header from a request when its value is "true." While the Overwrite header appears to duplicate the functionality of the If-Match: * header of HTTP/1.1, If-Match applies only to the Request-URI, and not to the Destination of a COPY or MOVE.
         Overwrite = "Overwrite" ":" ("true" | "false")
    
    If there is a conflict and the Overwrite header equals "true", or is absent and thus defaults to "true", then the method MUST fail with a 409 Conflict.

    3.11.4 Destroy Header

    When deleting a resource the client often wishes to specify exactly what sort of delete is being enacted. The Destroy header, used with the Mandatory header, allows the client to specify the end result they desire. The Destroy header is specified as follows:
  • The Undelete token requests that, if possible, the resource should be left in a state such that it can be undeleted. The server is not required to honor this request.
  • The NoUndelete token requests that the resource MUST NOT be left in a state such that it can be undeleted.
  • The VersionDestroy token includes the functionality of the NoUndelete token and extends it to include having the server remove all versioning references to the resource that it has control over.
    DestroyHeader = "Destroy" ":" #Choices

    Choices = "VersionDestroy" | "NoUndelete" | "Undelete" | token |"<" URI ">" ; a token extension MUST NOT be used unless it is specified in a RFC16, otherwise a URI MUST be used for extensions.

    3.11.5 Collection-Member Header

    The Collection-Member header specifies the URI of an external resource to be added/deleted to/from a collection.
         CollectionMember = "Collection-Member" ":" URI
    

    3.12 Links

    3.12.1 Source Link Property Type


    Name: http://www.ietf.org/standards/dav/link/source
    Purpose: The destination of the source link identifies the resource that contains the unprocessed source of the linkís source.
    Schema: http://www.ietf.org/standards/dav/link/
    Parent: Any
    Value: An XML document with zero or more link XML elements.
    Discussion: The source of the link (src) is typically the URI of the output resource on which the link is defined, and there is typically only one destination (dst) of the link, which is the URI where the unprocessed source of the resource may be accessed. When more than one link destination exists, this specification asserts no policy on ordering.

    4 State Tokens

    4.1 Overview

    4.1.1 Problem Description

    There are times when a principal will want to predicate successful execution of a method on the current state of a resource. While HTTP/1.1 provides a mechanism for conditional execution of methods using entity tags via the "If-Match" and "If-None-Match" headers, the mechanism is not sufficiently extensible to express conditional statements involving more generic state indicators, such as lock tokens.

    The fundamental issue with entity tags is that they can only be generated by a resource. However there are times when a client will want to be able to share state tokens between resources, potentially on different servers, as well as be able to generate certain types of lock tokens without first having to communicate with a server.

    For example, a principal may wish to require that resource B have a certain state in order for a method to successfully execute on resource A. If the client submits an e-tag from resource B to resource A, then A has no way of knowing that the e-tag is meant to describe resource B.

    Another example occurs when a principal wishes to predicate the successful completion of a method on the absence of any locks on a resource. It is not sufficient to submit an "If-None-Match: *" as this refers to the existence of an entity, not of a lock.

    This draft defines the term "state token" as an identifier for a state of a resource. The sections below define requirements for state tokens and provide a state token syntax, along with two new headers which can accept the new state token syntax.

    4.1.2 Solution Requirements

    4.1.2.1 Syntax

    Self-Describing. A state token must be self describing such that upon inspecting a state token it is possible to determine what sort of state token it is, what resource(s) it applies to, and what state it represents.

    This self-describing nature allows servers to accept tokens from other servers and potentially be able to coordinate state information cross resource and cross site through standardized protocols. For example, the execution of a request on resource A can be predicated on the state of resource B, where A and B are potentially on different servers.

    Client Generable. The state token syntax must allow, when appropriate, for clients to generate a state token without having first communicated with a server.

    One drawback of entity tags is that they are set by the server, and there is no interoperable algorithm for calculating an entity tag. Consequently, a client cannot generate an entity tag from a particular state of a resource. However, a state token which encodes an MD5 state hash could be calculated by a client based on a client-held state of a resource, and then submitted to a server in a conditional method invocation.

    Another potential use for client generable state tokens is for a client to generate lock tokens with wild card fields, and hence be able to express conditionals such as: "only execute this GET if there are no write locks on this resource."

    4.1.2.2 Conditonals

    Universal. A solution must be applicable to all requests. Positive and Negative. Conditional expressions must allow for the expression of both positive and negative state requirements.

    4.2 State Token Syntax

    State tokens are URLs employing the following syntax:
    State-Token = "StateToken:" Type ":" Resources ":" State-Info
    Type = "Type" "=" Caret-encoded-URL
    Resources = "Res" "=" Caret-encoded-URL
    Caret-encoded-URL = "^" Resource "^"
    Resource = <A URI where all "^" characters are escaped>
    State-Info = *(uchar | reserved)  ; uchar, reserved defined
    section 3.2.1 of RFC 2068
    

    This proposal has created a new URL scheme for state tokens because a state token names a network resource using its normal name, which is typically state-invariant, along with additional information that specifies a particular state of the resource. Encoding the state information into the native URL scheme of the network resource was not felt to be safe, since freedom from name space collisions could not be guaranteed. If this proposal is accepted, the StateToken URL scheme will need to be defined and registered with IANA.

    State Token URLs begin with the URL scheme name "StateToken" rather than the name of the particular state token type they represent in order to make the URL self describing. Thus it is possible to examine the URL and know, at a minimum, that it is a state token.

    Labeled name/value pairs are used within the token to allow new fields to be added. Processors of state tokens MUST be prepared to accept the fields in whatever order they are present and MUST ignore any fields they do not understand. The "Type" field specifies the type of the state information encoded in the state token. A URL is used in order to avoid namespace collisions.

    The "Res" field identifies the resource for which the state token specifies a particular state. Since commas and spaces are acceptable URL characters, a caret is used to delimit a URL. Since a caret is an acceptable URL character, any instances of it must be escaped using the % escape convention.

    The State-Info production is expanded upon in descriptions of specific state token types, and is intended to contain the state description information for a particular state token.

    4.3 State Token Conditional Headers

    4.3.1 If-State-Match

    If-State-Match = "If-State-Match" ":" ("AND" | "OR") 1#("<" State-Token ">")
    

    The If-State-Match header is intended to have similar functionality to the If-Match header defined in section 14.25 of RFC 2068.

    If the AND keyword is used and all of the state tokens identify the state of the resource, then the server MAY perform the requested method. If the OR keyword is used and any of the state tokens identifies the current state of the resource, then server MAY perform the requested method. If neither of the keyword requirements is met, the server MUST NOT perform the requested method, and MUST return a 412 (Precondition Failed) response.

    4.3.2 If-None-State-Match

    If-None-State-Match = "If-None-State-Match" ":" 1#("<" State-Token ">")
    

    The If-None-State-Match header is intended to have similar functionality to the If-None-Match header defined in section 14.26 of RFC 2068.

    If any of the state tokens identifies the current state of the resource, the server MUST NOT perform the requested method. Instead, if the request method was GET, HEAD, INDEX, or GETMETA, the server SHOULD respond with a 304 (Not Modified) response, including the cache-related entity-header fields (particularly ETag) of the current state of the resource. For all other request methods, the server MUST respond with a status of 412 (Precondition Failed).

    If none of the state tokens identifies the current state of the resource, the server MAY perform the requested method.

    Note that the "AND" and "OR" keywords specified with the If-State-Match header are intentionally not defined for If-None-State-Match, because this functionality is not required.

    4.4 State Token Header

    State-Token-Header = "State-Token" ":" 1#("<" State-Token ">")
    

    The State Token header is intended to have similar functionality to the etag header defined in section 14.20 of RFC 2068. The purpose of the tag is to return state tokens defined on a resource in a response. The contents of the state-token are not guaranteed to be exhaustive and are generally used to return a new state token that has been defined as the result of a method. For example, if a LOCK method were successfully executed on a resource the response would include a state token header with the lock state token included.

    4.5 E-Tags

    E-tags have already been deployed using the If-Match and If-None-Match headers. Introducing two mechanisms to express e-tags would only confuse matters, therefore e-tags should continue to be expressed using quoted strings and the If-Match and If-None-Match headers.

    5 Locking

    5.1 Problem Description - Overview

    Locking is used to arbitrate access to a resource amongst principals that have equal access rights to that resource.

    This draft allows locks to vary over two parameters, the number of principals involved and the type of access to be granted. This draft will only provide for the definition of locking for one access type, write. However, the syntax is extensible enough to allow for the specification of other access types. It is a goal of this proposal that it use the same access verbs as will be defined in the access control draft.

    5.1.1 Exclusive Vs. Shared Locks

    The most basic form of LOCK is an exclusive lock. This is a lock where the access right in question is only granted to a single principal. The need for this arbitration results from a desire to avoid having to constantly merge results. In fact, many users so dislike having to merge that they would rather serialize their access to a resource rather than have to constantly perform merges.

    However, there are times when the goal of a lock is not to exclude others from exercising an access right but rather to provide a mechanism for principals to indicate that they intend to exercise their access right. Shared locks are provided for this case. A shared lock allows multiple principals to receive a lock, hence any principal with appropriate access can get the lock.

    With shared locks there are two trust sets that affect a resource. The first trust set is created by access permissions. Principals who are trusted, for example, may have permission to write the resource, those who are not, don't. Among those who have access permission to write the resource, the set of principals who have taken out a shared lock also must trust each other, creating a (probably) smaller trust set within the access permission write set.

    Starting with every possible principal on the Internet, in most situations the vast majority of these principals will not have write access to a given resource. Of the small number who do have write access, some principals may decide to guarantee their edits are free from overwrite conflicts by using exclusive write locks in conjunction with a precondition header (If-State-Match) that checks for existence of the lock prior to writing the resource. Others may decide they trust their collaborators (the potential set of collaborators being the set of principals who have write permission) and use a shared lock, which informs their collaborators that a principal is potentially working on the resource.

    The WebDAV extensions to HTTP do not need to provide all of the communications paths necessary for principals to coordinate their activities. When using shared locks, principals may use any out of band communication channel to coordinate their work (e.g., face-to-face interaction, written notes, post-it notes on the screen, telephone conversation, email). The intent of a shared lock is to let collaborators know who else is potentially working on a resource.

    Why not use exclusive write locks all the time? Experience from initial Web distributed authoring systems has indicated that exclusive write locks are often too rigid. An exclusive write lock is used to enforce a particular editing process: take out exclusive write lock, read the resource, perform edits, write the resource, release the lock. What happens if the lock isn't released? While the time-out mechanism provides one solution, if you need to force the release of a lock immediately, it doesn't help much. Granted, an administrator can release the lock for you, but this could become a significant burden for large sites. Further, what if the administrator can't be reached immediately?

    Despite their potential problems, exclusive write locks are extremely useful, since often a guarantee of freedom from overwrite conflicts is exactly what is needed. The solution: provide exclusive write locks, but also provide a less strict mechanism in the form of shared locks which can be used by a set of people who trust each other and who have access to a communications channel external to HTTP which can be used to negotiate writing to the resource.

    5.1.2 Required Support

    A DAV compliant server is not required to support locking in any form. If the server does support locking it may choose to support any combination of exclusive and shared locks for any access types.

    The reason for this flexibility is that server implementers have said that they are willing to accept minimum requirements on all services but locking. Locking policy strikes to the very heart of their resource management and versioning systems and they require control over what sort of locking will be made available. For example, some systems only support shared write locks while others only provide support for exclusive write locks. As each system is sufficiently different to merit exclusion of certain locking features, the authors are proposing that locking be allowed as the sole axis of negotiation within DAV.

    5.2 LOCK Method

    5.2.1 Operation

    A lock method invocation creates the lock specified by the Lock-Info header on the request-URI. Lock method requests SHOULD NOT have a request body. A user-agent SHOULD submit an Owner header field with a lock request.

    A successful response to a lock invocation MUST include a Lock-Token header. If the server supports a time based lock removal mechanism on the resource, a successful lock invocation SHOULD return a Time-Out header.

    5.2.2 Effect of Locks on Properties and Containers

    By default a lock affects the entire state of the resource, including its associated properties. As such it is illegal to specify a lock on a property. For containers, a lock also affects the ability to add or remove members. The nature of the effect depends upon the type of access control involved. The Depth header expresses the general semantics of a LOCK method request when invoked on a collection (note that specific lock types may restrict the effect of a lock, for example limiting the allowable values of the Depth header):
  • A Depth header (defined in the namespace draft) may be used on a LOCK method when the LOCK method is applied to a collection resource. The legal values for Depth on a LOCK are 0, 1, and Infinity. A Depth of 0 instructs the resource to just lock the container. As previously mentioned, depending on the type of lock, the lock affects the ability to add or remove members of the container.
  • A Depth of 1 means that the container is locked and a LOCK is executed on the containerís propagate members with a Depth of 0 and If-Range, If-Modified-Since, If-Unmodified-Since, If-Match and If-None-Match headers are dropped. However, the effects of the LOCK MUST be atomic in that either the container and all of its members are locked or no lock is granted. The result of a Depth 1 lock is a single lock token which represents the lock on the container and all of its members. This lock token may be used in an If-State-Match or If-Not-State-Match header against any of the resources covered by the lock. Since the lock token represents a lock on all the resources, an UNLOCK using that token will remove the lock from all included resources, not just the resource the UNLOCK was executed on.
  • A Depth of infinity means that the LOCK is recursively executed, with a Depth of infinity, on the collection and all of its propagate members and all of their propagate members. As with a Depth of 1, the LOCK must be granted in total or not at all. Otherwise the lock operates in the same manner as a Depth of 1 lock.

    The default behavior when locking a container is to act as if a "Depth: 0" header had been placed on the method.

    5.2.3 Locking Replicated Resources

    Some servers automatically replicate resources across multiple URLs. In such a circumstance the server MAY only accept a lock on one of the URLs if the server can guarantee that the lock will be honored across all the URLs.

    5.2.4 Interaction with other Methods

    Only two methods, MOVE and DELETE, have side effects which involve locks. When a resource is moved, its lock SHOULD be moved with it. However this may not always be possible and there is currently no proposal to create a header which would specify that the lock request should fail if the resourceís locks can not be maintained. A COPY MUST NOT copy any locks on the source resource over to the destination resource. Deleting a resource MUST remove all locks on the resource.

    5.2.5 Lock Compatibility Table

    The table below describes the behavior that occurs when a lock request is made on a resource.
    Lock request
    Current lock state
    Shared Lock Exclusive Lock
    None True True
    Shared Lock True False
    Exclusive Lock False False*

    Legend: True = lock MAY be granted. False = lock MUST NOT be granted. *=if the principal requesting the lock is the owner of the lock, the lock MAY be regranted.

    The current lock state of a resource is given in the leftmost column, and lock requests are listed in the first row. The intersection of a row and column gives the result of a lock request. For example, if a shared lock is held on a resource, and an exclusive lock is requested, the table entry is "false", indicating the lock must not be granted.

    If an exclusive lock is re-requested by the principal who owns the lock, the lock MAY be regranted. If the lock is regranted, the same lock token that was previously issued MUST be returned.

    5.2.6 Status Codes

  • 412 "Precondition Failed" - The included state-token was not enforceable on this resource.
  • 416 "Locked" - The resource is locked so the method has been rejected.

    5.2.7 Example

    LOCK /workspace/webdav/proposal.doc HTTP/1.1
    Host: webdav.sb.aol.com
    Lock-Info: LockType=Write LockScope=Exclusive
    Owner: <http://www.ics.uci.edu/~ejw/contact.html>
    
    HTTP/1.1 200 OK
    State-Token: StateToken:Type=^DAV:/LOCK/DAVLOCK^:Res=^http://www.ics.uci.edu/workspace/webdav/proposal.doc^:LockType=Write:LockScope=Exclusive:ServerID=12382349AdfFFF
    Time-Out: ClockType=Activity TimeType=second;604800
    

    This example shows the successful creation of an exclusive write lock on resource http://webdav.sb.aol.com/workspace/webdav/proposal.doc. The resource http://www.ics.uci.edu/~ejw/contact.html contains contact information for the owner of the lock. The server has an activity-based timeout policy in place on this resource, which causes the lock to automatically be removed after 1 week (604800 seconds). The response has a Lock-Token header that gives the state token URL for the lock token generated by this lock request.

    5.2.8 Lock-Info Request Header

    The Lock-Info header specifies the scope and type of a lock for a LOCK method request. The syntax specification below is extensible, allowing new type and scope identifiers to be added.
    LockInfo = "Lock-Info" ":" DAVLockType SP DAVLockScope CRLF
    DAVLockType = "LockType" "=" DAVLockTypeValue
    DAVLockTypeValue = ("Write" | *(uchar | reserved))
    DAVLockScope = "LockScope" "=" DAVLockScopeValue
    DAVLockScopeValue = ("Exclusive" |"Shared" | *(uchar | reserved))
    

    5.2.9 Owner Request Header

    5.2.9.1 Problem Description

    When discovering the list of owners of locks on a resource, a principal may want to be able to contact the owner directly. For this to be possible the lock discovery mechanism must provide enough information for the lock owner to be contacted.

    5.2.9.2 Solution Requirements

    Not all systems have authentication procedures that provide sufficient information to identify a particular user in a way that is meaningful to a human. In addition, many systems that do have sufficient information, such as a name and e-mail address, do not have the ability to associate this information with the lock discovery mechanism. Therefore a means is needed to allow principals to provide authentication in a manner which will be meaningful to a human.

    The From header (defined in RFC 2068), which contains only an email mailbox, is not sufficient for the purposes of quick identification. When desperately looking for someone to remove a lock, e-mail is often not sufficient. A telephone number (cell number, pager number, etc.) would be better. Furthermore, the email address in the From field may or may not support including the owners name and that name is often set to an alias anyway. Therefore a header more flexible than From is required.

    5.2.9.3 Syntax

    Owner = "Owner" ":" (("<" URI ">")  | quoted-string)
    
    The URI SHOULD provide a means for either directly contacting the principal (such as a telephone number or e-mail URI), or for discovering the principal (such as the URL of a homepage). The quoted string SHOULD provide a means for directly contacting the principal, such as a name and telephone number.

    5.2.10 Time-Out Header

    5.2.10.1 Problem Description

    In a perfect world principals take out locks, use the resource as needed, and then remove the lock when it is no longer needed. However, this scenario is frequently not completed, leaving active but unused locks. Reasons for this include client programs crashing and loosing information about locks, users leaving their systems for the day and forgetting to remove their locks, etc. As a result of this behavior, servers need to establish a policy by which they can remove a lock without input from the lock owner. Once such a policy is instituted, the server also needs a mechanism to inform the principal of the policy.

    5.2.10.2 Solution Requirements

    There are two basic lock removal policies, administrator and time based remove. In the first case a principal other than the lock owner has sufficient access rights to order the lock removed, even though they did not take it out. User-agents MUST assume that such a mechanism is available and thus locks may arbitrarily disappear at any time. If their actions require confirmation of the existence of a lock then the If-State headers are available.

    The second solution, is the time based removal policy. Activity based systems set a timer as soon as the lock is taken out. Every time a method is executed on the resource, the timer is reset. If the timer runs out, the lock is removed.

    Finally, some systems only allow locks to exist for the duration of a session, where a session is defined as the time when the HTTP connection that was used to take out the lock remains connected. This mechanism is used to allow programs which are likely to be improperly exited, such as JAVA programs running in a browser, to take out locks without leaving a lot of ownerless locks around when they are improperly exited.

    5.2.10.3 Syntax

    TimeOut = "Time-Out" ":" ((TimeOutType SP Session) | TimeOutVal |
              Session) CRLF
    TimeOutType = ClockType SP TimeType
    ClockType = "ClockType" "=" ClockTypeValue
    ClockTypeValue = "Activity"
    TimeType = "TimeType" "=" TimeTypeValue
    TimeTypeValue = "Second" ";" DAVTimeOutVal
    DAVTimeOutVal = 1*digit
    Session = "Session" "=" ("Yes" | "No")
    
    The "Second" TimeType specifies the number of seconds that may elapse before the lock is automatically removed. A server MUST not generate a time out value for "second" greater than 2^32-1.

    If no time based system is in use then a Time-Out header MUST NOT be returned. The Time-Out header MUST only be returned in a response to a LOCK request.When session is set to yes then whatever clocktype and timetype is being used, their effects are scoped within that particular session. So an absolute lock with a ten day expiration period will only remain active so long as the session remains active. A DAVTimeOutVal value must be greater than zero.

    Clients MAY include TimeOut headers in their LOCK requests. However the server is not required to honor or even consider the request. The primary purpose in allowing clients to submit a TimeOut header is to inform the server if the client is requesting a session based lock. If a timeout is associated with the lock, the server MUST return a TimeOut header with a valid value.

    5.2.11 State-Token Header

    5.2.11.1 Problem Definition

    Program A, used by User A, takes out a write lock on a resource. Program B, also run by User A, then proceeds to perform a PUT to the locked resource. The PUT will succeed because locks are associated with a principal, not a program, and thus program B, because it is acting with principal Aís credential, will be allowed to perform the PUT. In reality program B had no knowledge of the lock and had it had such knowledge, would not have overwritten the resource. Hence, a mechanism is needed to prevent different programs from accidentally ignoring locks taken out by other programs with the same authorization.

    5.2.11.2 Solution Requirement

    The solution must not require principals to perform discovery in order to prevent accidental overwrites as this could cause race conditions.

    The solution must not require that clients guess what sorts of locks might be used and use if-state-match headers with wildcards to prevent collisions. The problem with trying to "guess" which locks are being used is that new lock types might be introduced, and the program would not know to "guess them". So, for example, a client might put in an if-state-match header with a wildcard specifying that if any write lock is outstanding then the operation should fail. However a new read/write lock could be introduced which the client would not know to put in the header.

    5.2.11.3 State-Token Header

    The State-Token header is returned in a successful response to the LOCK method or is used as a request header with the UNLOCK method.

    The State-Token header containing a lock token owned by the request principal is used by the principal on arbitrary method to indicate that the principal is aware of the specified lock. If the State-Token header with the appropriate lock token is not included the request MUST be rejected, even though the requesting principal has authorization to make modifications specified by the lock type. This injunction does not apply to methods that are not affected by the principalís lock.

    For example, Program A, used by user A, takes out a write lock on a resource. Program A then makes a number of PUT requests on the locked resource, all the requests contain a State-Token header which includes the write lock state token. Program B, also run by User A, then proceeds to perform a PUT to the locked resource. However program B was not aware of the existence of the lock and so does not include the appropriate state-token header. The method is rejected even though principal A is authorized to perform the PUT. Program B can, if it so chooses, now perform lock discovery and obtain the lock token. Note that program A and B can perform GETs without using the state-token header because the ability to perform a GET is not affected by a write lock. Note that having a lock state token provides no special access rights. Anyone can find out anyone elseís lock state token by performing lock discovery. Locks are to be enforced based upon whatever authentication mechanism is used by the server, not based on the secrecy of the token values.

    5.3 Write Lock

    A write lock prevents a principal without the lock from successfully executing a PUT, POST, DELETE, MKCOL, PROPPATCH, PATCH, ADDREF or DELREF on the locked resource. All other methods, GET in particular, function independent of the lock.

    While those without a write lock may not alter a property on a resource it is still possible for the values of live properties to change, even while locked, due to the requirements of their schemas. Only dead properties and live properties defined to respect locks are guaranteed to not change while locked.

    It is possible to assert a write lock on a null resource in order to lock the name. Please note, however, that locking a null resource effectively makes the resource non-null as the resource now has lock related properties defined on it.

    Write locking a container also prevents adding or removing members of the container. This means that attempts to PUT/POST a resource into the immediate name space of the write locked container MUST fail if the principal requesting the action does not have the write lock on the container. In order to keep the behavior of locking containers consistent all locks on containers MUST contain a Depth header equal to infinity, any other value is illegal.

    5.4 Lock Tokens

    5.4.1 Problem Description

    It is possible that once a lock has been granted it may be removed without the lock ownerís knowledge. This can cause serialization problems if the lock owner executes methods thinking their lock is still in effect. Thus a mechanism is needed for a principal to predicate the successful execution of a message upon the continuing existence of a lock.

    5.4.2 Proposed Solution

    The proposed solution is to provide a lock token in the response of a lock request. The lock token is a type of state token and describes a particular lock. The same lock token must never be repeated on a particular resource. This prevents problems with long held outstanding lock tokens being confused with newer tokens. This uniqueness requirement is the same as for e-tags. This requirement also allows for tokens to be submitted across resources and servers without fear of confusion.

    5.4.3 Lock Token Definition

    The lock token is returned in the State-Token header in the response to a LOCK method. The lock token can also be discovered through lock discovery on a resource.

    Lock-Token-URL = "StateToken:" Type ":" Resources ":" State-Info
    Type = "Type" "=" "^DAV:/LOCK/DAVLOCK^"
    Resources = "Res" "=" 1*("^" Caret-Encoded-URI "^")
    Caret-Encoded-URI = <This is a URI which has all "^"s % encoded.>
    State-Info = DAVLockScope ":" DAVLockType ":" ServerID  ;
    DAVLockScope, DAVLockType defined in Lock-Info header
    ServerID = "ServerID" "=" *(uchar | reserved)
    

    The ServerID is a field for use by the server. Its most basic purpose is to put in a unique identifier to guarantee that a server will never confuse an old lock token with a newer one. However the server is free to use the field to record whatever information it deems fit. The field is opaque to clients.

    5.5 UNLOCK Method

    5.5.1 Problem Definition

    The UNLOCK method removes the lock identified by the lock token in the State-Token header from the Request-URI.

    5.5.2 Example

    UNLOCK /workspace/webdav/proposal.doc HTTP/1.1
    Host: webdav.sb.aol.com
    State-Token: StateToken:Type=^DAV:/LOCK/DAVLOCK^:Res=^http://www.
    ics.uci.edu/workspace/webdav/proposal.doc^:LockType=Write:LockSco
    pe=Exclusive:ServerID=12382349AdfFFF
    
    HTTP/1.1 200 OK
    

    In this example, the lock from example of Section 2.9 is removed from the resource at http://webdav.sb.aol.com/workspace/webdav/proposal.doc

    5.6 Discovery Mechanisms

    5.6.1 Lock Type Discovery

    5.6.1.1 Problem Definition

    Since server lock support is optional, a client trying to lock a resource on a server can either try the lock and hope for the best or can perform some form of discovery to determine what lock types the server actually supports, then formulate a supported request. This is known as lock type discovery. Lock type discovery is not the same as discovering what access control types are supported, as there may be access control types without corresponding lock types.

    5.6.1.2 SupportedLock Property


    Name: http://www.ietf.org/standards/dav/lock/supportedlock
    Purpose: To provide a listing of the lock types supported by the resource.
    Schema: http://www.ietf.org/standards/dav/
    Values: An XML document containing zero or more LockEntry XML elements.
    Description: The SupportedLock property of a resource returns a listing of the combinations of scope and access types which may be specified in a lock request on the resource. Note that the actual contents are themselves controlled by access controls so a server is not required to provide information the client is not authorized to see. If SupportedLock is available on "*" then it MUST define the set of locks allowed on all resources on that server.

    5.6.1.3 LOCKENTRY XML Element


    Name: http://www.ietf.org/standards/dav/lockentry
    Purpose: Defines a DAVLockType/LockScope pair which may be legally used with a LOCK on the specified resource.
    Schema: HYPERLINK http://www.ietf.org/standards/dav/
    Parent: A SupportedLock entry
    Values: LockType LockScope

    5.6.1.4 LOCKTYPE XML Element


    Name: http://www.ietf.org/standards/dav/locktype
    Purpose: Lists a DAVLockType
    Schema: http://www.ietf.org/standards/dav/
    Parent: LOCKENTRY
    Values: DAVLockTypeValue

    5.6.1.5 LOCKSCOPE XML Element


    Name: http://www.ietf.org/standards/dav/lockscope
    Purpose: Lists a DAVLockScope
    Schema: http://www.ietf.org/standards/dav/
    Parent: LOCKENTRY
    Values: DAVLockScopeValue

    5.6.2 Active Lock Discovery

    5.6.2.1 Problem Definition

    If another principal locks a resource that a principal wishes to access, it is useful for the second principal to be able to find out who the first principal is.

    5.6.2.2 Solution Requirements

    The lock discovery mechanism should provide a list of who has the resource locked, what locks they have, and what their lock tokens are. The lock tokens are useful in shared lock situations where two principals in particular may want to guarantee that they do not overwrite each other. The lock tokens are also useful for administrative purposes so that an administrator can remove a lock by referring to its token.

    5.6.2.3 LOCKDISCOVERY Property


    Name: http://www.ietf.org/standards/dav/lockdiscovery
    Purpose: To discover what locks are active on a resource
    Schema: http://www.ietf.org/standards/dav/
    Values: An XML document containing zero or more ActiveLock XML elements.
    Description: The LOCKDISCOVERY property returns a listing of who has a lock, what type of lock they have, the time out type and the time remaining on the time out, and the associated lock token. The server is free to withhold any or all of this information if the requesting principal does not have sufficient access rights to see the requested data.

    5.6.2.4 ACTIVELOCK XML Element


    Name: http://www.ietf.org/standards/dav/activelock
    Purpose: A multivalued XML element that describes a particular active lock on a resource
    Schema: http://www.ietf.org/standards/dav/
    Parent: A LOCKDISCOVERY entry
    Values: LOCKTYPE LOCKSCOPE OWNER TIMEOUT LOCKTOKEN

    5.6.2.5 OWNER XML Element


    Name: http://www.ietf.org/standards/dav/lock/owner
    Purpose: Returns owner information
    Schema: http://www.ietf.org/standards/dav/
    Parent: ACTIVELOCK
    Values: XML:REF | {any valid XML string}

    5.6.2.6 TIMEOUT XML Element


    Name: http://www.ietf.org/standards/dav/timeout
    Purpose: Returns information about the timeout associated with the lock
    Schema: http://www.ietf.org/standards/dav/
    Parent: ACTIVELOCK
    Values: CLOCKTYPE TIMETYPE TIMEOUTVAL

    5.6.2.7 CLOCKTYPE XML Element


    Name: http://www.ietf.org/standards/dav/clocktype
    Purpose: Returns the clock type used with this lock
    Schema: http://www.ietf.org/standards/dav/
    Parent: TIMEOUT
    Values: ClockTypeValue

    5.6.2.8 TIMETYPE XML Element


    Name: http://www.ietf.org/standards/dav/clocktype
    Purpose: Returns the time type used with this lock
    Schema: http://www.ietf.org/standards/dav/
    Parent: TIMEOUT
    Values: TimeTypeValue

    5.6.2.9 TIMEOUTVAL XML Element


    Name: http://www.ietf.org/standards/dav/timeoutval
    Purpose: Returns the amount of time left on the lock
    Schema: http://www.ietf.org/standards/dav/
    Parent: TIMEOUT
    Values: DAVTimeOutVal

    5.6.2.10 LOCKTOKEN XML Element


    Name: http://www.ietf.org/standards/dav/statetoken
    Purpose: Returns the lock token
    Schema: http://www.ietf.org/standards/dav/
    Parent: ACTIVELOCK
    Values: XML:REF
    Description: The REF contains a Lock-Token-URL.

    6 Version Control

    [TBD]

    7 Internationalization Support

    [TBD]

    8 Security Considerations

    [TBD]

    9 Acknowledgements

    Terry Allen, Harald Alvestrand, Alan Babich, Dylan Barrell, Bernard Chester, Dan Connolly, Jim Cunningham, Ron Daniel, Jr., Keith Dawson, Mark Day, Martin Duerst, David Durand, Lee Farrell, Chuck Fay, Roy Fielding, Mark Fisher, Alan Freier, George Florentine, Jim Gettys, Phill Hallam-Baker, Dennis Hamilton, Steve Henning, Alex Hopmann, Andre van der Hoek, Ben Laurie, Paul Leach, Ora Lassila, Karen MacArthur, Steven Martin, Larry Masinter, Michael Mealling, Keith Moore, Henrik Nielsen, Kenji Ota, Bob Parker, Glenn Peterson, Jon Radoff, Saveen Reddy, Henry Sanders, Christopher Seiwald, Judith Slein, Mike Spreitzer, Einar Stefferud, Ralph Swick, Kenji Takahashi, Robert Thau, Sankar Virdhagriswaran, Fabio Vitali, Gregory Woodhouse, Lauren Wood

    10 References

    [Berners-Lee, 1997] T. Berners-Lee, "Metadata Architecture." Unpublished white paper, January 1997. http://www.w3.org/pub/WWW/DesignIssues/Metadata.html.

    [Bray, Sperberg-McQueen, 1997] T. Bray, C. M. Sperberg-McQueen, "Extensible Markup Language (XML): Part I. Syntax", WD-xml-lang.html, http://www.w3.org/pub/WWW/TR/WD-xml-lang.html.

    [Connolly et al, 1997] D. Connolly, R. Khare, H.F. Nielsen, "PEP - an Extension Mechanism for HTTP", Internet draft, work-in-progress. draft-ietf-http-pep-04.txt, ftp://ds.internic.net/internet-drafts/draft-ietf-http-pep-04.txt.

    [Fielding et al., 1997] R. Fielding, J. Gettys, J. Mogul, H. Frystyk, T. Berners-Lee, "Hypertext Transfer Protocol --HTTP/1.1." RFC 2068. U.C. Irvine, DEC, MIT/LCS. January, 1997.

    [Lasher, Cohen, 1995] R. Lasher, D. Cohen, "A Format for Bibliographic Records," RFC 1807. Stanford, Myricom. June, 1995.

    [Maloney, 1996] M. Maloney, "Hypertext Links in HTML." Internet draft (expired), work-in-progress, January, 1996.

    [MARC, 1994] Network Development and MARC Standards, Office, ed. 1994. "USMARC Format for Bibliographic Data", 1994. Washington, DC: Cataloging Distribution Service, Library of Congress. [Miller et al., 1996] J. Miller, T. Krauskopf, P. Resnick, W. Treese, "PICS Label Distribution Label Syntax and Communication Protocols" Version 1.1, W3C Recommendation REC-PICS-labels-961031. http://www.w3.org/pub/WWW/TR/REC-PICS-labels-961031.html

    [Slein et al., 1997] J. A. Slein, F. Vitali, E. J. Whitehead, Jr., D. Durand, "Requirements for Distributed Authoring and Versioning on the World Wide Web." Internet-draft, work-in-progress, draft-ietf-webdav-requirements-03.txt, ftp://ds.internic.net/internet-drafts/draft-ietf-webdav-requirements-03.txt.

    [WebDAV, 1997] WEBDAV Design Team. "A Proposal for Web Metadata Operations." Unpublished manuscript. http://www.ics.uci.edu/~ejw/authoring/proposals/metadata.html

    [Weibel et al., 1995] S. Weibel, J. Godby, E. Miller, R. Daniel, "OCLC/NCSA Metadata Workshop Report." http://purl.oclc.org/metadata/dublin_core_report.

    [Yergeau, 1997] F. Yergeau, "UTF-8, a transformation format of Unicode and ISO 10646", Internet Draft, work-in-progress, draft-yergeau-utf8-rev-00.txt, http://www.internic.net/internet-drafts/draft-yergeau-utf8-rev-00.txt.

    11 Authors' Addresses

    Y. Y. Goland
    Microsoft Corporation
    One Microsoft Way
    Redmond, WA 98052-6399
    Email yarong@microsoft.com
    
    E. J. Whitehead, Jr.
    Dept. Of Information and Computer Science
    University of California, Irvine
    Irvine, CA 92697-3425
    Email: ejw@ics.uci.edu
    
    A. Faizi
    Netscape
    685 East Middlefield Road
    Mountain View, CA 94043
    Email: asad@netscape.com
    
    S. R Carter
    Novell
    1555 N. Technology Way
    M/S ORM F111
    Orem, UT 84097-2399
    Email srcarter@novell.com
    
    D. Jensen
    Novell
    1555 N. Technology Way
    M/S ORM F111
    Orem, UT 84097-2399
    Email dcjensen@novell.com