--- draft-fielding-url-syntax-09.txt Tue Oct 21 21:01:58 1997 +++ draft-fielding-url-syntax-10.txt Thu Nov 6 19:19:30 1997 @@ -1,10 +1,10 @@ Network Working Group T. Berners-Lee, MIT/LCS INTERNET-DRAFT R. Fielding, U.C. Irvine -draft-fielding-url-syntax-09 L. Masinter, Xerox Corporation -Expires six months after publication date October 21, 1997 +draft-fielding-url-syntax-10 L. Masinter, Xerox Corporation +Expires six months after publication date November 06, 1997 - Uniform Resource Locators (URL): Generic Syntax and Semantics + Uniform Resource Identifiers (URI): Generic Syntax and Semantics Status of this Memo @@ -28,40 +28,40 @@ Abstract - A Uniform Resource Locator (URL) is a compact string representation - of a location for use in identifying an abstract or physical - resource. This document defines the general syntax and semantics - of URLs, including both absolute and relative locators, and - guidelines for their use; it revises and replaces the generic - definitions in RFC 1738 and RFC 1808. + A Uniform Resource Identifier (URI) is a compact string + representation of a location (URL) or name (URN) for use in + identifying an abstract or physical resource. This document defines + the general syntax and semantics of URIs, including both absolute and + relative forms, and guidelines for their use; it revises and replaces + the generic definitions in RFC 1738 and RFC 1808. 1. Introduction - Uniform Resource Locators (URLs) provide a simple and extensible - means for identifying a resource by its location. This - specification of URL syntax and semantics is derived from concepts - introduced by the World Wide Web global information initiative, - whose use of such objects dates from 1990 and is described in - "Universal Resource Identifiers in WWW" [RFC1630]. The - specification of URLs is designed to meet the recommendations laid - out in "Functional Recommendations for Internet Resource Locators" - [RFC1736]. + Uniform Resource Identifiers (URIs) provide a simple and extensible + means for identifying a resource. This specification of URI syntax + and semantics is derived from concepts introduced by the World Wide + Web global information initiative, whose use of such objects dates + from 1990 and is described in "Universal Resource Identifiers in WWW" + [RFC1630]. The specification of URIs is designed to meet the + recommendations laid out in "Functional Recommendations for Internet + Resource Locators" [RFC1736] and "Functional Requirements for Uniform + Resource Names" [RFC1737]. This document updates and merges "Uniform Resource Locators" [RFC1738] and "Relative Uniform Resource Locators" [RFC1808] in - order to define a single, general syntax for all URLs. It excludes + order to define a single, general syntax for all URIs. It excludes those portions of RFC 1738 that defined the specific syntax of individual URL schemes; those portions will be updated as separate - documents, as will the process for registration of new URL schemes. + documents, as will the process for registration of new URI schemes. This document does not discuss the issues and recommendation for dealing with characters outside of the US-ASCII character set; those recommendations are discussed in a separate document. All significant changes from the prior RFCs are noted in Appendix G. -1.1 Overview of URLs +1.1 Overview of URIs - URLs are characterized by the following definitions: + URIs are characterized by the following definitions: Uniform Uniformity of syntax and semantics allows the mechanism for @@ -69,10 +69,10 @@ to locate those resources and the operations applied to those resources once they have been located. New types of resources, access mechanisms, and operations can be introduced without - changing the protocols and data formats that use URLs. - Uniformity of syntax means that the same locator is used + changing the protocols and data formats that use URIs. + Uniformity of syntax means that the same identifier is used independent of the locale, character representation, or - system type of the user entering the URL. + system type of the user entering the URI. Resource A resource can be anything that has identity. Familiar @@ -89,33 +89,66 @@ which it currently corresponds---changes over time, provided that the conceptual mapping is not changed in the process. - Locator - A locator is an object that identifies a resource by its - location. In the case of URLs, the object is a sequence of - characters with a restricted syntax. An absolute locator - identifies a location independent of any context, whereas a - relative locator identifies a location relative to the - context in which it is found. - - URLs are used to `locate' resources by providing an abstract - identification of the resource location. Having located a resource, - a system may perform a variety of operations on the resource, as - might be characterized by such words as `access', `update', - `replace', or `find attributes'. - -1.2. URL, URN, and URI - - URLs are a subset of Uniform Resource Identifiers (URI), which also - includes the notion of Uniform Resource Names (URN). A URN differs - from a URL in that it identifies a resource in a - location-independent fashion (see [RFC1737]). This specification - restricts its discussion to URLs. The syntax and semantics of other - URIs are defined by a separate set of specifications, although - it is expected that any URI notation would have a compatible syntax. - -1.3. Example URLs + Identifier + An identifier is an object that can act as a reference to + something that has identity. In the case of URIs, the object + is a sequence of characters with a restricted syntax. An + absolute identifier refers to a resource independent of the + context in which the identifier is used, whereas a relative + identifier refers to a resource by describing the difference + within a hierarchical namespace between the current context + and an absolute identifier of the resource. + + Having identified a resource, a system may perform a variety of + operations on the resource, as might be characterized by such words + as `access', `update', `replace', or `find attributes'. + +1.2. URI, URL, and URN + + A URI can be further classified as a locator, a name, or both. + Uniform Resource Locators (URL) is the subset of URI that can be used + to `locate' resources by providing an abstract identification of the + resource location within the identifier (i.e., by using common + network name resolution mechanisms to identify the mechanisms for + accessing a resource). Uniform Resource Names (URN) is the subset + of URI that are intended to remain globally unique and persistent + even when the resource ceases to exist or becomes unavailable. + + The URI scheme (Section 4.1) defines the namespace of the URI, and + thus may further restrict the syntax and semantics of identifiers + using that scheme. This specification defines those elements of the + URI syntax which are either required of all URI schemes or are common + to many URI schemes. It thus defines the syntax and semantics that + are needed to implement a scheme-independent parsing mechanism for + URI references, such that the scheme-dependent handling of a URI can + be postponed until the scheme-dependent semantics are needed. We use + the term URL below when describing syntax or semantics that only + apply to locators. + + Although many URL schemes are named after protocols, this does not + imply that the only way to access the URL's resource is via the named + protocol. Gateways, proxies, caches, and name resolution services + might be used to access some resources, independent of the protocol + of their origin, and the resolution of some URLs may require the use + of more than one protocol (e.g., both DNS and HTTP are typically used + to access an "http" URL's resource when it can't be found in a local + cache). + + The "urn" scheme has been reserved to establish the requirements for + a standardized URN namespace, as defined in "URN Syntax" [RFC2141] + and its related specifications. + + Most of the examples in this specification demonstrate URLs, since + they allow the most varied use of the syntax and often have a + hierarchical namespace. A parser of the URI syntax is capable of + parsing both URL and URN references as a generic URI; once the scheme + is determined, the scheme-specific parsing can be performed on the + generic URI components. In other words, the URI syntax is a superset + of the syntax of all URI schemes. + +1.3. Example URIs - The following examples illustrate URLs which are in common use. + The following examples illustrate URIs which are in common use. ftp://ftp.is.co.za/rfc/rfc1808.txt -- ftp scheme for File Transfer Protocol services @@ -135,65 +168,55 @@ telnet://melvyl.ucop.edu/ -- telnet scheme for interactive services via the TELNET Protocol - Many URL schemes have been defined. The scheme defines the - namespace of the URL. Although many URL schemes are named after - protocols, this does not imply that the only way to access the - URL's resource is via the named protocol. Gateways, proxies, - caches, and name resolution services might be used to access some - resources, independent of the protocol of their origin, and the - resolution of some URLs may require the use of more than one - protocol (e.g., both DNS and HTTP are typically used to access an - "http" URL's resource when it can't be found in a local cache). +1.4. Hierarchical URIs and Relative Forms -1.4. Hierarchical URLs and Relative Forms - - URL schemes may support a hierarchical naming system, where the + URI schemes may support a hierarchical naming system, where the hierarchy of the name is denoted by a "/" delimiter separating the - components in the scheme. There is a `relative' form of URL reference - which is used in conjunction with a `base' URL (of a hierarchical - scheme) to produce another URL. The syntax of hierarchical URLs is - described in Section 4, and the relative URL calculation is described + components in the scheme. There is a `relative' form of URI reference + which is used in conjunction with a `base' URI (of a hierarchical + scheme) to produce another URI. The syntax of hierarchical URIs is + described in Section 4, and the relative URI calculation is described in Section 5. -1.5. URL Transcribability +1.5. URI Transcribability - The URL syntax was designed with global transcribability as one of - its main concerns. A URL is a sequence of characters from a very + The URI syntax was designed with global transcribability as one of + its main concerns. A URI is a sequence of characters from a very limited set, i.e. the letters of the basic Latin alphabet, digits, - and a few special characters. A URL may be represented in a + and a few special characters. A URI may be represented in a variety of ways: e.g., ink on paper, pixels on a screen, or a sequence of octets in a coded character set. The interpretation of - a URL depends only on the characters used and not how those + a URI depends only on the characters used and not how those characters are represented in a network protocol. The goal of transcribability can be described by a simple scenario. Imagine two colleagues, Sam and Kim, sitting in a pub at an international conference and exchanging research ideas. Sam asks - Kim for a location to get more information, so Kim writes the URL + Kim for a location to get more information, so Kim writes the URI for the research site on a napkin. Upon returning home, Sam takes - out the napkin and types the URL into a computer, which then + out the napkin and types the URI into a computer, which then retrieves the information to which Kim referred. There are several design concerns revealed by the scenario: - o A URL is a sequence of characters, which is not always + o A URI is a sequence of characters, which is not always represented as a sequence of octets. - o A URL may be transcribed from a non-network source, and thus + o A URI may be transcribed from a non-network source, and thus should consist of characters which are most likely to be able to be typed into a computer, within the constraints imposed by keyboards (and related input devices) across languages and locales. - o A URL often needs to be remembered by people, and it is easier - for people to remember a URL when it consists of meaningful + o A URI often needs to be remembered by people, and it is easier + for people to remember a URI when it consists of meaningful components. These design concerns are not always in alignment. For example, it - is often the case that the most meaningful name for a URL component + is often the case that the most meaningful name for a URI component would require characters which cannot be typed into some systems. - The ability to transcribe the resource location from one medium to - another was considered more important than having its URL consist + The ability to transcribe the resource identifier from one medium to + another was considered more important than having its URI consist of the most meaningful of components. In local and regional contexts and with improving technology, users might benefit from being able to use a wider range of characters; such use is not @@ -214,7 +237,7 @@ the syntax requirements. The second convention is a BNF-like grammar, used to define the - formal URL syntax. The grammar is that of [RFC822], except that + formal URI syntax. The grammar is that of [RFC822], except that "|" is used to designate alternatives. Briefly, rules are separated from definitions by an equal "=", indentation is used to continue a rule definition over more than one line, literals are quoted with "", @@ -224,10 +247,10 @@ element; n defaults to 0. Unlike many specifications which use a BNF-like grammar to define the - bytes (octets) allowed by a protocol, the URL grammar is defined in + bytes (octets) allowed by a protocol, the URI grammar is defined in terms of characters. Each literal in the grammar corresponds to the character it represents, rather than to the octet encoding of that - character in any particular coded character set. How a URL is + character in any particular coded character set. How a URI is represented in terms of bits and bytes on the wire is dependent upon the character encoding of the protocol used to transport it, or the charset of the document which contains it. @@ -249,32 +272,32 @@ alphanum = alpha | digit - The complete URL syntax is collected in Appendix A. + The complete URI syntax is collected in Appendix A. -2. URL Characters and Escape Sequences +2. URI Characters and Escape Sequences - URLs consist of a restricted set of characters, primarily chosen to + URIs consist of a restricted set of characters, primarily chosen to aid transcribability and usability both in computer systems and in non-computer communications. Characters used conventionally as - delimiters around URLs were excluded. The restricted set of + delimiters around URIs were excluded. The restricted set of characters consists of digits, letters, and a few graphic symbols were chosen from those common to most of the character encodings and input facilities available to Internet users. - Within a URL, characters are either used as delimiters, or to + Within a URI, characters are either used as delimiters, or to represent strings of data (octets) within the delimited portions. Octets are either represented directly by a character (using the US-ASCII character for that octet) or by an escape encoding. This representation is elaborated below. -2.1 URLs and non-ASCII characters +2.1 URIs and non-ASCII characters - While URLs are sequences of characters and those characters are + While URIs are sequences of characters and those characters are used (within delimited sections) to represent sequences of octets, in some cases those sequences of octets are used (via a 'charset' or character encoding scheme) to represent sequences of characters: - URL char. sequence <-> octet sequence <-> original char. sequence + URI char. sequence <-> octet sequence <-> original char. sequence In cases where the original character sequence contains characters that are strictly within the set of characters defined in the @@ -286,39 +309,40 @@ In general practice, many different character encoding schemes are used in the second mapping (between sequences of represented characters and sequences of octets) and there is generally no - representation in the URL itself of which mapping was used. While - there is a strong desire to provide for a general and uniform - mapping between more general scripts and URLs, the standard for - such use is outside of the scope of this document. + representation in the URI itself of which mapping was used unless + the URI scheme requires a specific mapping. While there is a strong + desire to provide for a general and uniform mapping between more + general scripts and URIs, the standard for such use is outside of the + scope of this document. - More systematic treatment of character encoding within URLs is + More systematic treatment of character encoding within URIs is currently under development. 2.2. Reserved Characters - Many URLs include components consisting of or delimited by, certain + Many URIs include components consisting of or delimited by, certain special characters. These characters are called "reserved", since - their usage within the URL component is limited to their reserved - purpose. If the data for a URL component would conflict with the + their usage within the URI component is limited to their reserved + purpose. If the data for a URI component would conflict with the reserved purpose, then the conflicting data must be escaped before - forming the URL. + forming the URI. reserved = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" The "reserved" syntax class above refers to those characters which - are allowed within a URL, but which may not be allowed within a - particular component of the generic URL syntax; they are used as + are allowed within a URI, but which may not be allowed within a + particular component of the generic URI syntax; they are used as delimiters of the components described in Section 4.3. Characters in the "reserved" set are not reserved in all contexts. - The set of characters actually reserved within any given URL + The set of characters actually reserved within any given URI component is defined by that component. In general, a character is - reserved if the semantics of the URL changes if the character is + reserved if the semantics of the URI changes if the character is replaced with its escaped US-ASCII encoding. 2.3. Unreserved Characters - Data characters which are allowed in a URL but do not have a reserved + Data characters which are allowed in a URI but do not have a reserved purpose are called unreserved. These include upper and lower case letters, decimal digits, and a limited set of punctuation marks and symbols. @@ -329,7 +353,7 @@ "*" | "'" | "(" | ")" | "," Unreserved characters can be escaped without changing the semantics - of the URL, but this should not be done unless the URL is being used + of the URI, but this should not be done unless the URI is being used in a context which does not allow the unescaped character to appear. 2.4. Escape Sequences @@ -353,27 +377,28 @@ 2.4.2. When to Escape and Unescape - A URL is always in an "escaped" form, since escaping or unescaping - a completed URL might change its semantics. Normally, the only - time escape encodings can safely be made is when the URL is being + A URI is always in an "escaped" form, since escaping or unescaping + a completed URI might change its semantics. Normally, the only + time escape encodings can safely be made is when the URI is being created from its component parts; each component may have its own set of characters which are reserved, so only the mechanism responsible for generating or interpreting that component can determine whether or not escaping a character will change its - semantics. Likewise, a URL must be separated into its components + semantics. Likewise, a URI must be separated into its components before the escaped characters within those components can be safely decoded. In some cases, data that could be represented by an unreserved character may appear escaped; for example, some of the unreserved - "mark" characters are automatically escaped by some systems. It is - safe to unescape these within the body of a URL. For example, - "%7e" is sometimes used instead of "~" in http URL path, but the - two can be used interchangeably. + "mark" characters are automatically escaped by some systems. If the + given URI scheme defines a canonicalization algorithm, then + unreserved characters may be unescaped according to that algorithm. + For example, "%7e" is sometimes used instead of "~" in an http URL + path, but the two are equivalent for an http URL. Because the percent "%" character always has the reserved purpose of being the escape indicator, it must be escaped as "%25" in order to - be used as data within a URL. Implementers should be careful not to + be used as data within a URI. Implementers should be careful not to escape or unescape the same string more than once, since unescaping an already unescaped string might lead to misinterpreting a percent data character as another escaped character, or vice versa in the @@ -381,29 +406,29 @@ 2.4.3. Excluded US-ASCII Characters - Although they are disallowed within the URL syntax, we include here + Although they are disallowed within the URI syntax, we include here a description of those US-ASCII characters which have been excluded and the reasons for their exclusion. The control characters in the US-ASCII coded character set are not - used within a URL, both because they are non-printable and because + used within a URI, both because they are non-printable and because they are likely to be misinterpreted by some control mechanisms. control = The space character is excluded because significant spaces may - disappear and insignificant spaces may be introduced when URLs are + disappear and insignificant spaces may be introduced when URIs are transcribed or typeset or subjected to the treatment of - word-processing programs. Whitespace is also used to delimit URLs + word-processing programs. Whitespace is also used to delimit URIs in many contexts. space = The angle-bracket "<" and ">" and double-quote (") characters are - excluded because they are often used as the delimiters around URLs + excluded because they are often used as the delimiters around URIs in text documents and protocol fields. The character "#" is - excluded because it is used to delimit a URL from a fragment - identifier in URL references (Section 3). The percent character "%" + excluded because it is used to delimit a URI from a fragment + identifier in URI references (Section 3). The percent character "%" is excluded because it is used for the encoding of escaped characters. @@ -416,135 +441,129 @@ unwise = "{" | "}" | "|" | "\" | "^" | "[" | "]" | "`" Data corresponding to excluded characters must be escaped in order - to be properly represented within a URL. - -3. URL-based references and URLs + to be properly represented within a URI. - In practice, resource locators consist not only of complete URLs, - but other resource references which contain either an absolute - or relative URL form, and may be followed by a fragment identifier. - The terminology around the use of URLs has been confusing. +3. URI References - The term "URL-reference" is used here to denote the common usage of - a resource locator. A URL reference may be absolute or relative, + The term "URI-reference" is used here to denote the common usage of + a resource identifier. A URI reference may be absolute or relative, and may have additional information attached in the form of a - fragment identifier. However, "the URL" which results from such a - reference includes only the absolute URL after the fragment - identifier (if any) is removed and after any relative URL is + fragment identifier. However, "the URI" which results from such a + reference includes only the absolute URI after the fragment + identifier (if any) is removed and after any relative URI is resolved to its absolute form. Although it is possible to limit - the discussion of URL syntax and semantics to that of the absolute - result, most usage of URLs is within general URL references, and it - is impossible to obtain the URL from such a reference without also + the discussion of URI syntax and semantics to that of the absolute + result, most usage of URIs is within general URI references, and it + is impossible to obtain the URI from such a reference without also parsing the fragment and resolving the relative form. - URL-reference = [ absoluteURL | relativeURL ] [ "#" fragment ] + URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ] - The syntax for relative URLs is a shortened form of that for absolute - URLs, where some prefix of the URL is missing and certain path + The syntax for relative URIs is a shortened form of that for absolute + URIs, where some prefix of the URI is missing and certain path components ("." and "..") have a special meaning when interpreting a relative path. - When a URL reference is used to perform a retrieval action on the + When a URI reference is used to perform a retrieval action on the identified resource, the optional fragment identifier, separated from - the URL by a crosshatch ("#") character, consists of additional + the URI by a crosshatch ("#") character, consists of additional reference information to be interpreted by the user agent after the retrieval action has been successfully completed. As such, it is not - part of a URL, but is often used in conjunction with a URL. The + part of a URI, but is often used in conjunction with a URI. The format and interpretation of fragment identifiers is dependent on the media type of the retrieval result. - fragment = *urlc + fragment = *uric - A URL reference which does not contain a URL is a reference to the - current document. In other words, an empty URL reference within a + A URI reference which does not contain a URI is a reference to the + current document. In other words, an empty URI reference within a document is interpreted as a reference to the start of that document, and a reference containing only a fragment identifier is a reference to the identified fragment of that document. Traversal of such a reference should not result in an additional retrieval action. - However, if the URL reference occurs in a context that is always + However, if the URI reference occurs in a context that is always intended to result in a new request, as in the case of HTML's FORM - element, then an empty URL reference represents the base URL of the - current document and should be replaced by that URL when transformed + element, then an empty URI reference represents the base URI of the + current document and should be replaced by that URI when transformed into a request. -4. Generic URL Syntax +4. Generic URI Syntax 4.1. Scheme Just as there are many different methods of access to resources, - there are a variety of schemes for describing the location of such - resources. The URL syntax consists of a sequence of components - separated by reserved characters, with the first component defining - the semantics for the remainder of the URL string. + there are a variety of schemes for identifying such resources. The + URI syntax consists of a sequence of components separated by reserved + characters, with the first component defining the semantics for the + remainder of the URI string. - In general, absolute URLs are written as follows: + In general, absolute URIs are written as follows: : - An absolute URL contains the name of the scheme being used () + An absolute URI contains the name of the scheme being used () followed by a colon (":") and then a string (the ) whose interpretation depends on the scheme. Scheme names consist of a sequence of characters. The lower case letters "a"--"z", digits, and the characters plus ("+"), period ("."), and hyphen ("-") are allowed. For resiliency, programs - interpreting URLs should treat upper case letters as equivalent to + interpreting URIs should treat upper case letters as equivalent to lower case in scheme names (e.g., allow "HTTP" as well as "http"). scheme = 1*( alpha | digit | "+" | "-" | "." ) - Relative URL references are distinguished from absolute URLs in that + Relative URI references are distinguished from absolute URIs in that they do not begin with a scheme name. Instead, the scheme is - inherited from the base URL, as described in Section 5.2. + inherited from the base URI, as described in Section 5.2. -4.2. Opaque and Hierarchical URLs +4.2. Opaque and Hierarchical URIs - The URL syntax does not require that the scheme-specific-part have + The URI syntax does not require that the scheme-specific-part have any general structure or set of semantics which is common among all - URLs. However, a subset of URLs do share a common syntax for - representing hierarchical relationships within the locator namespace. - This generic-URL syntax is used in interpreting relative URLs. + URIs. However, a subset of URIs do share a common syntax for + representing hierarchical relationships within the namespace. + This generic-URI syntax is used in interpreting relative URIs. - absoluteURL = generic-URL | opaque-URL + absoluteURI = generic-URI | opaque-URI - opaque-URL = scheme ":" *urlc + opaque-URI = scheme ":" *uric - generic-URL = scheme ":" relativeURL + generic-URI = scheme ":" relativeURI - The separation of the URL grammar into and + The separation of the URI grammar into and is redundant, since both rules will successfully parse any string of - characters. The distinction is simply to clarify that a - parser of relative URL references (Section 5) will view a URL as a - generic-URL, whereas a handler of absolute references need only view - it as an opaque-URL. + characters. The distinction is simply to clarify that a + parser of relative URI references (Section 5) will view a URI as a + generic-URI, whereas a handler of absolute references need only view + it as an opaque-URI. - URLs which are hierarchical in nature use the slash "/" character for + URIs which are hierarchical in nature use the slash "/" character for separating hierarchical components. For some file systems, a "/" - character (used to denote the hierarchical structure of a URL) is the - delimiter used to construct a file name hierarchy, and thus the URL + character (used to denote the hierarchical structure of a URI) is the + delimiter used to construct a file name hierarchy, and thus the URI path will look similar to a file pathname. This does NOT imply that - the resource is a file or that the URL maps to an actual filesystem + the resource is a file or that the URI maps to an actual filesystem pathname. -4.3. URL Syntactic Components +4.3. URI Syntactic Components - The URL syntax is dependent upon the scheme. Some schemes use + The URI syntax is dependent upon the scheme. Some schemes use reserved characters like "?" and ";" to indicate special components, while others just consider them to be part of the path. However, - most URL schemes use a common sequence of four main components to - define the location of a resource + most URI schemes use a common sequence of four main components: ://? - each of which, except , may be absent from a particular URL. - For example, some URL schemes do not allow a component, and + each of which, except , may be absent from a particular URI. + For example, some URI schemes do not allow a component, and others do not use a component. 4.3.1. Site Component - Many URL schemes include a top hierarchical element for a naming + Many URI schemes include a top hierarchical element for a naming authority, such that the namespace defined by the remainder of the - URL is governed by that authority. This component is + URI is governed by that authority. This component is typically defined by an Internet-based server or a scheme-specific registry of naming authorities. @@ -552,18 +571,18 @@ The component is preceded by a double slash "//" and is terminated by the next slash "/", question-mark "?", or by the end of - the URL. Within the component, the characters ":", "@", "?", + the URI. Within the component, the characters ":", "@", "?", and "/" are reserved. The structure of a registry-based naming authority is specific to the - URL scheme, but constrained to the allowed characters for . + URI scheme, but constrained to the allowed characters for . authority = *( unreserved | escaped | ";" | ":" | "@" | "&" | "=" | "+" ) URL schemes that involve the direct use of an IP-based protocol to a specified server on the Internet use a common syntax for the - component of the URL's scheme-specific data: + component of the URI's scheme-specific data: @: @@ -581,7 +600,7 @@ Some URL schemes use the format "user:password" in the field. This practice is NOT RECOMMENDED, because the passing of - authentication information in clear text (such as URLs) has proven to + authentication information in clear text (such as URIs) has proven to be a security risk in almost every case where it has been used. The host is a domain name of a network host, or its IPv4 address as @@ -618,8 +637,8 @@ host by a colon. If the port is omitted, the default port number is assumed. - A site component is not required for a URL scheme to make use of - relative references. A base URL without a site component implies + A site component is not required for a URI scheme to make use of + relative references. A base URI without a site component implies that any relative reference will also be without a site component. 4.3.2. Path Component @@ -648,35 +667,35 @@ The query component is a string of information to be interpreted by the resource. - query = *urlc + query = *uric Within a query component, the characters "/", "&", "=", and "+" are reserved. -4.4. Parsing a URL Reference +4.4. Parsing a URI Reference - A URL reference is typically parsed according to the four main - components in order to determine what components are present and - whether or not the reference is relative or absolute. The individual - components are then parsed for their subparts and to verify their - validity. A reference is parsed as if it is a generic-URL, even - though it might be considered opaque by later processes. + A URI reference is typically parsed according to the four main + components and fragment identifier in order to determine what + components are present and whether the reference is relative or + absolute. The individual components are then parsed for their + subparts and to verify their validity. A reference is parsed as if + it is a generic-URI, even though it might be considered opaque by + later processes. Although the BNF defines what is allowed in each component, it is ambiguous in terms of differentiating between a site component and a path component that begins with two slash characters. The greedy algorithm is used for disambiguation: the left-most matching rule - soaks up as much of the URL reference string as it is capable of + soaks up as much of the URI reference string as it is capable of matching. In other words, the site component wins. Readers familiar with regular expressions should see Appendix B for a concrete parsing example and test oracle. - -5. Relative URL References +5. Relative URI References It is often the case that a group or "tree" of documents has been - constructed to serve a common purpose; the vast majority of URLs in + constructed to serve a common purpose; the vast majority of URIs in these documents point to locations within the tree rather than outside of it. Similarly, documents located at a particular site are much more likely to refer to other resources at that site than @@ -686,13 +705,13 @@ independent of their location and access scheme. For instance, it is possible for a single set of hypertext documents to be simultaneously accessible and traversable via each of the "file", "http", and "ftp" - schemes if the documents refer to each other using relative URLs. + schemes if the documents refer to each other using relative URIs. Furthermore, such document trees can be moved, as a whole, without changing any of the relative references. Experience within the WWW has demonstrated that the ability to perform relative referencing is necessary for the long-term usability of embedded URLs. - relativeURL = net_path | abs_path | rel_path + relativeURI = net_path | abs_path | rel_path A relative reference beginning with two slash characters is termed a network-path reference. Such references are rarely used. @@ -718,34 +737,37 @@ (Section 5.2). Authors should be aware that a path segment which contains a colon - character cannot be used as the first segment of a relative URL path + character cannot be used as the first segment of a relative URI path (e.g., "this:that"), because it would be mistaken for a scheme name. It is therefore necessary to precede such segments with other segments (e.g., "./this:that") in order for them to be referenced as a relative path. - It is not necessary for all URLs within a given scheme to be - restricted to the generic-URL syntax, since the hierarchical - properties of that syntax are only necessary when relative URLs are + It is not necessary for all URIs within a given scheme to be + restricted to the generic-URI syntax, since the hierarchical + properties of that syntax are only necessary when relative URIs are used within a particular document. Documents can only make use of - relative URLs when their base URL fits within the generic-URL syntax. + relative URIs when their base URI fits within the generic-URI syntax. It is assumed that any document which contains a relative reference - will also have a base URL that obeys the syntax. In other words, - relative URLs cannot be used within a document that has an unsuitable - base URL. - -5.1. Establishing a Base URL - - The term "relative URL" implies that there exists some absolute "base - URL" against which the relative reference is applied. Indeed, the - base URL is necessary to define the semantics of any relative URL + will also have a base URI that obeys the syntax. In other words, + relative URIs cannot be used within a document that has an unsuitable + base URI. + + Some URI schemes do not allow a hierarchical syntax matching the + generic-URI syntax, and thus cannot use relative references. + +5.1. Establishing a Base URI + + The term "relative URI" implies that there exists some absolute "base + URI" against which the relative reference is applied. Indeed, the + base URI is necessary to define the semantics of any relative URI reference; without it, a relative reference is meaningless. In order - for relative URLs to be usable within a document, the base URL of + for relative URIs to be usable within a document, the base URI of that document must be known to the parser. - The base URL of a document can be established in one of four ways, + The base URI of a document can be established in one of four ways, listed below in order of precedence. The order of precedence can be - thought of in terms of layers, where the innermost defined base URL + thought of in terms of layers, where the innermost defined base URI has the highest precedence. This can be visualized graphically as: .----------------------------------------------------------. @@ -755,20 +777,20 @@ | | | | .----------------------------------. | | | | | | | | | | | | | | | | | | `----------------------------------' | | | | - | | | | (5.1.1) Base URL embedded in the | | | | + | | | | (5.1.1) Base URI embedded in the | | | | | | | | document's content | | | | | | | `----------------------------------------' | | | - | | | (5.1.2) Base URL of the encapsulating entity | | | + | | | (5.1.2) Base URI of the encapsulating entity | | | | | | (message, document, or none). | | | | | `----------------------------------------------' | | - | | (5.1.3) URL used to retrieve the entity | | + | | (5.1.3) URI used to retrieve the entity | | | `----------------------------------------------------' | - | (5.1.4) Default Base URL is application-dependent | + | (5.1.4) Default Base URI is application-dependent | `----------------------------------------------------------' -5.1.1. Base URL within Document Content +5.1.1. Base URI within Document Content - Within certain document media types, the base URL of the document can + Within certain document media types, the base URI of the document can be embedded within the content itself such that it can be readily obtained by a parser. This can be useful for descriptive documents, such as tables of content, which may be transmitted to others through @@ -776,86 +798,86 @@ USENET news). It is beyond the scope of this document to specify how, for each - media type, the base URL can be embedded. It is assumed that user + media type, the base URI can be embedded. It is assumed that user agents manipulating such media types will be able to obtain the appropriate syntax from that media type's specification. An example - of how the base URL can be embedded in the Hypertext Markup Language + of how the base URI can be embedded in the Hypertext Markup Language (HTML) [RFC1866] is provided in Appendix D. - A mechanism for embedding the base URL within MIME container types + A mechanism for embedding the base URI within MIME container types (e.g., the message and multipart types) is defined by MHTML [RFC2110]. Protocols that do not use the MIME message header syntax, but which do allow some form of tagged metainformation to be included within messages, may define their own syntax for defining the base - URL as part of a message. + URI as part of a message. -5.1.2. Base URL from the Encapsulating Entity +5.1.2. Base URI from the Encapsulating Entity - If no base URL is embedded, the base URL of a document is defined by + If no base URI is embedded, the base URI of a document is defined by the document's retrieval context. For a document that is enclosed within another entity (such as a message or another document), the - retrieval context is that entity; thus, the default base URL of the - document is the base URL of the entity in which the document is + retrieval context is that entity; thus, the default base URI of the + document is the base URI of the entity in which the document is encapsulated. -5.1.3. Base URL from the Retrieval URL +5.1.3. Base URI from the Retrieval URI - If no base URL is embedded and the document is not encapsulated + If no base URI is embedded and the document is not encapsulated within some other entity (e.g., the top level of a composite entity), - then, if a URL was used to retrieve the base document, that URL shall - be considered the base URL. Note that if the retrieval was the - result of a redirected request, the last URL used (i.e., that which - resulted in the actual retrieval of the document) is the base URL. + then, if a URI was used to retrieve the base document, that URI shall + be considered the base URI. Note that if the retrieval was the + result of a redirected request, the last URI used (i.e., that which + resulted in the actual retrieval of the document) is the base URI. -5.1.4. Default Base URL +5.1.4. Default Base URI If none of the conditions described in Sections 5.1.1--5.1.3 apply, - then the base URL is defined by the context of the application. + then the base URI is defined by the context of the application. Since this definition is necessarily application-dependent, failing - to define the base URL using one of the other methods may result in + to define the base URI using one of the other methods may result in the same content being interpreted differently by different types of application. It is the responsibility of the distributor(s) of a document - containing relative URLs to ensure that the base URL for that + containing relative URIs to ensure that the base URI for that document can be established. It must be emphasized that relative - URLs cannot be used reliably in situations where the document's - base URL is not well-defined. + URIs cannot be used reliably in situations where the document's + base URI is not well-defined. 5.2. Resolving Relative References to Absolute Form - This section describes an example algorithm for resolving URL - references which might be relative to a given base URL. + This section describes an example algorithm for resolving URI + references which might be relative to a given base URI. - The base URL is established according to the rules of Section 5.1 and + The base URI is established according to the rules of Section 5.1 and parsed into the four main components as described in Section 4.4. Note that only the scheme component is required to be present in the - base URL; the other components may be empty or undefined. A + base URI; the other components may be empty or undefined. A component is undefined if its preceding separator does not appear in - the URL reference; the path component is never undefined, though it - may be empty. The base URL's query component is not used by the + the URI reference; the path component is never undefined, though it + may be empty. The base URI's query component is not used by the resolution algorithm and may be discarded. - For each URL reference, the following steps are performed in order: + For each URI reference, the following steps are performed in order: - 1) The URL reference is parsed into the potential four components and + 1) The URI reference is parsed into the potential four components and fragment identifier, as described in Section 4.4. 2) If the path component is empty and the scheme, site, and query components are undefined, then it is a reference to the current - document and we are done. Otherwise, the reference URL's query + document and we are done. Otherwise, the reference URI's query and fragment components are defined as found (or not found) within - the URL reference and not inherited from the base URL. + the URI reference and not inherited from the base URI. 3) If the scheme component is defined, indicating that the reference starts with a scheme name, then the reference is interpreted as an - absolute URL and we are done. Otherwise, the reference URL's - scheme is inherited from the base URL's scheme component. + absolute URI and we are done. Otherwise, the reference URI's + scheme is inherited from the base URI's scheme component. 4) If the site component is defined, then the reference is a network-path and we skip to step 7. Otherwise, the reference - URL's site is inherited from the base URL's site component, - which will also be undefined if the URL scheme does not use a + URI's site is inherited from the base URI's site component, + which will also be undefined if the URI scheme does not use a site component. 5) If the path component begins with a slash character ("/"), then @@ -863,10 +885,10 @@ 6) If this step is reached, then we are resolving a relative-path reference. The relative path needs to be merged with the base - URL's path. Although there are many ways to do this, we will + URI's path. Although there are many ways to do this, we will describe a simple method using a separate string buffer. - a) All but the last segment of the base URL's path component is + a) All but the last segment of the base URI's path component is copied to the buffer. In other words, any characters after the last (right-most) slash character, if any, are excluded. @@ -893,15 +915,15 @@ complete path segments of "..", then the reference is considered to be in error. Implementations may handle this error by retaining these components in the resolved path - (i.e., treating them as part of the final URL), by removing + (i.e., treating them as part of the final URI), by removing them from the resolved path (i.e., discarding relative levels above the root), or by avoiding traversal of the reference. - h) The remaining buffer string is the reference URL's new path + h) The remaining buffer string is the reference URI's new path component. - 7) The resulting URL components, including any inherited from the - base URL, are recombined to give the absolute form of the URL + 7) The resulting URI components, including any inherited from the + base URI, are recombined to give the absolute form of the URI reference. Using pseudocode, this would be result = "" @@ -946,9 +968,9 @@ Resolution examples are provided in Appendix C. -6. URL Normalization and Equivalence +6. URI Normalization and Equivalence - In many cases, different URL strings may actually identify the + In many cases, different URI strings may actually identify the identical resource. For example, the host names used in URLs are actually case insensitive, and the URL is equivalent to . In general, the rules for @@ -961,14 +983,16 @@ 7. Security Considerations - A URL does not in itself pose a security threat. Users should beware + A URI does not in itself pose a security threat. Users should beware that there is no general guarantee that a URL, which at one time located a given resource, will continue to do so. Nor is there any guarantee that a URL will not locate a different resource at some later point in time, due to the lack of any constraint on how a given site apportions its namespace. Such a guarantee can only be obtained from the person(s) controlling that namespace and the - resource in question. + resource in question. A specific URI scheme may include additional + semantics, such as name persistence, if those semantics are required + of all naming authorities for that scheme. It is sometimes possible to construct a URL such that an attempt to perform a seemingly harmless, idempotent operation, such as the @@ -1005,8 +1029,8 @@ This document was derived from RFC 1738 [RFC1738] and RFC 1808 [RFC1808]; the acknowledgements in those specifications still apply. In addition, contributions by Lauren Wood, Martin Duerst, - Gisle Aas, Martijn Koster, Ryan Moats, Foteos Macrides and - Dave Kristol are gratefully acknowledged. + Gisle Aas, Martijn Koster, Ryan Moats, Foteos Macrides, Dave Kristol, + and Daniel LaLiberte are gratefully acknowledged. 9. References @@ -1042,6 +1066,8 @@ [RFC1736] Kunze, J., "Functional Recommendations for Internet Resource Locators", RFC 1736, IS&T, UC Berkeley, February 1995. +[RFC2141] Moats, R., "URN Syntax", RFC 2141, AT&T, May 1997. + [RFC1034] Mockapetris, P., "Domain Names - Concepts and Facilities", STD 13, RFC 1034, USC/Information Sciences Institute, November 1987. @@ -1137,14 +1163,14 @@ Appendices -A. Collected BNF for URLs +A. Collected BNF for URIs - URL-reference = [ absoluteURL | relativeURL ] [ "#" fragment ] - absoluteURL = generic-URL | opaque-URL - opaque-URL = scheme ":" *urlc - generic-URL = scheme ":" relativeURL + URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ] + absoluteURI = generic-URI | opaque-URI + opaque-URI = scheme ":" *uric + generic-URI = scheme ":" relativeURI - relativeURL = net_path | abs_path | rel_path + relativeURI = net_path | abs_path | rel_path net_path = "//" site [ abs_path ] abs_path = "/" rel_path rel_path = [ path_segments ] [ "?" query ] @@ -1173,11 +1199,11 @@ param = *pchar pchar = unreserved | escaped | ":" | "@" | "&" | "=" | "+" - query = *urlc + query = *uric - fragment = *urlc + fragment = *uric - urlc = reserved | unreserved | escaped + uric = reserved | unreserved | escaped reserved = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" unreserved = alpha | digit | mark mark = "$" | "-" | "_" | "." | "!" | "~" | @@ -1200,16 +1226,16 @@ "8" | "9" -B. Parsing a URL Reference with a Regular Expression +B. Parsing a URI Reference with a Regular Expression - As described in Section 4.4, the generic-URL syntax is not sufficient - to disambiguate the components of some forms of URL. Since the + As described in Section 4.4, the generic-URI syntax is not sufficient + to disambiguate the components of some forms of URI. Since the "greedy algorithm" described in that section is identical to the disambiguation method used by POSIX regular expressions, it is natural and commonplace to use a regular expression for parsing the - potential four components and fragment identifier of a URL reference. + potential four components and fragment identifier of a URI reference. - The following line is the regular expression for breaking-down a URL + The following line is the regular expression for breaking-down a URI reference into its components. ^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))? @@ -1244,17 +1270,17 @@ query = $7 fragment = $9 - and, going in the opposite direction, we can recreate a URL reference + and, going in the opposite direction, we can recreate a URI reference from its components using the algorithm in step 7 of Section 5.2. -C. Examples of Resolving Relative URL References +C. Examples of Resolving Relative URI References - Within an object with a well-defined base URL of + Within an object with a well-defined base URI of http://a/b/c/d;p?q - the relative URLs would be resolved as follows: + the relative URIs would be resolved as follows: C.1. Normal Examples @@ -1284,7 +1310,7 @@ C.2. Abnormal Examples Although the following abnormal examples are unlikely to occur in - normal practice, all URL parsers should be capable of resolving them + normal practice, all URI parsers should be capable of resolving them consistently. Each example uses the same base as above. An empty reference refers to the start of the current document. @@ -1293,14 +1319,14 @@ Parsers must be careful in handling the case where there are more relative path ".." segments than there are hierarchical levels in - the base URL's path. Note that the ".." syntax cannot be used to - change the site component of a URL. + the base URI's path. Note that the ".." syntax cannot be used to + change the site component of a URI. ../../../g = http://a/../g ../../../../g = http://a/../../g In practice, some implementations strip leading relative symbolic - elements (".", "..") after applying a relative URL calculation, based + elements (".", "..") after applying a relative URI calculation, based on the theory that compensating for obvious author errors is better than allowing the request to fail. Thus, the above two references will be interpreted as "http://a/g" by some implementations. @@ -1315,7 +1341,7 @@ g.. = http://a/b/c/g.. ..g = http://a/b/c/..g - Less likely are cases where the relative URL uses unnecessary or + Less likely are cases where the relative URI uses unnecessary or nonsensical forms of the "." and ".." complete path segments. ./../g = http://a/b/g @@ -1325,8 +1351,8 @@ g;x=1/./y = http://a/b/c/g;x=1/y g;x=1/../y = http://a/b/c/y - All client applications remove the query component from the base URL - before resolving relative URLs. However, some applications fail to + All client applications remove the query component from the base URI + before resolving relative URIs. However, some applications fail to separate the reference's query and/or fragment components from a relative path before merging it with the base path. This error is rarely noticed, since typical usage of a fragment never includes the @@ -1338,28 +1364,28 @@ g#s/./x = http://a/b/c/g#s/./x g#s/../x = http://a/b/c/g#s/../x - Some parsers allow the scheme name to be present in a relative URL - if it is the same as the base URL scheme. This is considered to be - a loophole in prior specifications of partial URLs [RFC1630]. Its + Some parsers allow the scheme name to be present in a relative URI + if it is the same as the base URI scheme. This is considered to be + a loophole in prior specifications of partial URIs [RFC1630]. Its use should be avoided. http:g = http:g http: = http: -D. Embedding the Base URL in HTML documents +D. Embedding the Base URI in HTML documents - It is useful to consider an example of how the base URL of a + It is useful to consider an example of how the base URI of a document can be embedded within the document's content. In this appendix, we describe how documents written in the Hypertext Markup - Language (HTML) [RFC1866] can include an embedded base URL. This - appendix does not form a part of the URL specification and should not + Language (HTML) [RFC1866] can include an embedded base URI. This + appendix does not form a part of the URI specification and should not be considered as anything more than a descriptive example. HTML defines a special element "BASE" which, when present in the "HEAD" portion of a document, signals that the parser should use - the BASE element's "HREF" attribute as the base URL for resolving - any relative URLs. The "HREF" attribute must be an absolute URL. + the BASE element's "HREF" attribute as the base URI for resolving + any relative URIs. The "HREF" attribute must be an absolute URI. Note that, in HTML, element and attribute names are case-insensitive. For example: @@ -1372,7 +1398,7 @@ A parser reading the example document should interpret the given - relative URL "../x" as representing the absolute URL + relative URI "../x" as representing the absolute URI @@ -1380,48 +1406,48 @@ obtained. -E. Recommendations for Delimiting URLs in Context +E. Recommendations for Delimiting URIs in Context - URLs are often transmitted through formats which do not provide a + URIs are often transmitted through formats which do not provide a clear context for their interpretation. For example, there are - many occasions when URLs are included in plain text; examples + many occasions when URIs are included in plain text; examples include text sent in electronic mail, USENET news messages, and, most importantly, printed on paper. In such cases, it is important - to be able to delimit the URL from the rest of the text, and in + to be able to delimit the URI from the rest of the text, and in particular from punctuation marks that might be mistaken for part - of the URL. + of the URI. - In practice, URLs are delimited in a variety of ways, but usually + In practice, URIs are delimited in a variety of ways, but usually within double-quotes "http://test.com/", angle brackets , or just using whitespace http://test.com/ - These wrappers do not form part of the URL. + These wrappers do not form part of the URI. - In the case where a fragment identifier is associated with a URL + In the case where a fragment identifier is associated with a URI reference, the fragment would be placed within the brackets as well - (separated from the URL with a "#" character). + (separated from the URI with a "#" character). In some cases, extra whitespace (spaces, linebreaks, tabs, etc.) - may need to be added to break long URLs across lines. The - whitespace should be ignored when extracting the URL. + may need to be added to break long URIs across lines. The + whitespace should be ignored when extracting the URI. No whitespace should be introduced after a hyphen ("-") character. Because some typesetters and printers may (erroneously) introduce a hyphen at the end of line when breaking a line, the interpreter of a - URL containing a line break immediately after a hyphen should ignore + URI containing a line break immediately after a hyphen should ignore all unescaped whitespace around the line break, and should be aware - that the hyphen may or may not actually be part of the URL. + that the hyphen may or may not actually be part of the URI. - Using <> angle brackets around each URL is especially recommended - as a delimiting style for URLs that contain whitespace. + Using <> angle brackets around each URI is especially recommended + as a delimiting style for URIs that contain whitespace. The prefix "URL:" (with or without a trailing space) was recommended as a way to used to help distinguish a URL from other bracketed designators, although this is not common in practice. - For robustness, software that accepts user-typed URLs should + For robustness, software that accepts user-typed URIs should attempt to recognize and strip both delimiters and embedded whitespace. @@ -1432,7 +1458,7 @@ net/rfc/>. Note the warning in . - contains the URL references + contains the URI references http://www.w3.org/Addressing/ ftp://ds.internic.net/rfc/ @@ -1471,17 +1497,17 @@ G.1. Additions - Section 3 (URL References) was added to stem the confusion - regarding "what is a URL" and how to describe fragment identifiers - given that they are not part of the URL, but are part of the URL + Section 3 (URI References) was added to stem the confusion + regarding "what is a URI" and how to describe fragment identifiers + given that they are not part of the URI, but are part of the URI syntax and parsing concerns. In addition, it provides a reference definition for use by other IETF specifications (HTML, HTTP, etc.) - which have previously attempted to redefine the URL syntax in order - to account for the presence of fragment identifiers in URL + which have previously attempted to redefine the URI syntax in order + to account for the presence of fragment identifiers in URI references. Section 2.4 was rewritten to clarify a number of misinterpretations - and to leave room for fully internationalized URLs. + and to leave room for fully internationalized URIs. Appendix F on abbreviated URLs was added to describe the shortened references often seen on television and magazine advertisements and @@ -1489,27 +1515,29 @@ G.2. Modifications from both RFC 1738 and RFC 1808 - Confusion regarding the terms "character encoding", the URL + Changed to URI syntax and semantics instead of just URL. + + Confusion regarding the terms "character encoding", the URI "character set", and the escaping of characters with % equivalents has (hopefully) been reduced. Many of the BNF rule names regarding the character sets have been changed to more accurately describe their purpose and to encompass all "characters" rather than just US-ASCII octets. Unless otherwise noted here, - these modifications do not affect the URL syntax. + these modifications do not affect the URI syntax. Both RFC 1738 and RFC 1808 refer to the "reserved" set of - characters as if URL-interpreting software were limited to a single + characters as if URI-interpreting software were limited to a single set of characters with a reserved purpose (i.e., as meaning something other than the data to which the characters correspond), - and that this set was fixed by the URL scheme. However, this has + and that this set was fixed by the URI scheme. However, this has not been true in practice; any character which is interpreted differently when it is escaped is, in effect, reserved. Furthermore, the interpreting engine on a HTTP server is often - dependent on the resource, not just the URL scheme. The + dependent on the resource, not just the URI scheme. The description of reserved characters has been changed accordingly. The plus "+" character was added to those in the "reserved" set, - since it is treated as reserved within some URL components. + since it is treated as reserved within some URI components. The tilde "~" character was added to those in the "unreserved" set, since it is extensively used on the Internet in spite of the @@ -1523,15 +1551,15 @@ The question-mark "?" character was removed from the set of allowed characters for the userinfo in the site component, since testing showed that many applications treat it as reserved for - separating the query component from the rest of the URL. + separating the query component from the rest of the URI. RFC 1738 specified that the path was separated from the site - portion of a URL by a slash. RFC 1808 followed suit, but with a + portion of a URI by a slash. RFC 1808 followed suit, but with a fudge of carrying around the separator as a "prefix" in order to describe the parsing algorithm. RFC 1630 never had this problem, since it considered the slash to be part of the path. In writing this specification, it was found to be impossible to accurately - describe and retain the difference between the two URLs + describe and retain the difference between the two URIs and without either considering the slash to be part of the path (as corresponds to actual practice) or creating a separate component just @@ -1551,7 +1579,7 @@ expected to handle the case where the ":" separator between host and port is supplied without a port. - The recommendations for delimiting URLs in context (Appendix E) have + The recommendations for delimiting URIs in context (Appendix E) have been adjusted to reflect current practice. G.4. Modifications from RFC 1808 @@ -1571,10 +1599,10 @@ fields defined by MHTML [RFC2110]. RFC 1808 described various schemes as either having or not having the - properties of the generic-URL syntax. However, the only requirement + properties of the generic-URI syntax. However, the only requirement is that the particular document containing the relative references - have a base URL which abides by the generic-URL syntax, regardless of - the URL scheme, so the associated description has been updated to + have a base URI which abides by the generic-URI syntax, regardless of + the URI scheme, so the associated description has been updated to reflect that. The BNF term has been replaced with , since the @@ -1587,7 +1615,7 @@ semicolon in a path segment does not affect the relative parsing of that segment. Therefore, parameters have been removed as a separate component and may now appear in any path segment. Their influence - has been removed from the algorithm for resolving a relative URL + has been removed from the algorithm for resolving a relative URI reference. The resolution examples in Appendix C have been modified to reflect this change.