System Architecture Concepts

Software System Architecture

• An significant Enterprise Software System Architecture example taken from DB2 Magazine, appearing in the following article (optional material)
• Example of the overall architecture for Catalyst.
• Another example software architecture modeled in UML
• Architectural views emphasize structure (or configuration) rather information, data, or work flow which may appear in System Specifications or Requirements (cf. Use Cases).
  

Software System Components

• Executable software systems, programs, functions, or computational methods (in object-oriented programs) with an interface (a composition of I/O resources).

Interfaces

• Composition of I/O resources that Require (consume), Use (reuse) or Provide (produce) application data object types, instance values, or component control signals (e.g., to automatically invoke other "helper" applications).

I/O Resources

• Application resources -- data object types, instance values, or component control signals (start, stop, suspend, resume, error, etc.) -- Input to, or Output from, a component
• (Optional) Functions or logical predicates that specify the range of acceptable values for each resource, or special values (e.g., "anomalies") that signify component processing exceptions.

Connectors

• Connectors are the key ingredient for "Enterprise Application Integration" that enable information, data, or work flow.
  
• Data communication mechanisms that enable the exchange or interchange of messages (data or control signals) between communicating components
• Point-to-Point Application Program (Component) Interfaces (APIs) that link a Component's Outputs to other Components' Inputs
• Messaging system for communicating (or transporting) messages between a sending/requesting component and a listening/receiving component.
• Text-based messages are a pervasive "network-centric" scheme for communicating messages via the Internet.
• Textual pattern manipulation languages like Perl, Tcl, Javascript/ECMAScript, and Python, together with textual "pipe-and-filter" connectors, are used most frequently in Web server-based enterprise applications.
• Email and Network News Servers can be used to asynchronously transport textual messages between system components (slowly) or between people via connection-based servers.
• HyperText Transfer Protocol (HTTP) or Simple Object Access Protocol (SOAP) can be used to asynchronously "request and retrieve" views of self-describing MIME object types (HTML Web pages, GIF/JPEG images, Quicktime MOVies, etc.) between system components communicating over the Internet (Web browsers and Web Servers) for viewing by people.
• User Datagram Protocol (UDP) is a low-level, best-effort data communication protocol that supports "instant messaging" between synchronously communicating components that act as peers (e.g., peer-to-peer applications) communicating over the Internet.
• UDP is a fast messaging mechanism for transferring small objects between a small number of peers.
• UDP is not a reliable transport mechanism, especially for large objects or communications involving large numbers of simultaneously chatting peers.
• Information bus: a "middleware" messaging system for broadcasting from one sending component to many other listening components, such as found in CORBA or products from TIBCO (The Information Bus COmpany).
• Multicast trees are a scalable scheme for broadcasting from one source/server to very many clients (servers), who then rebroadcast to their own clients (servers) via intermediate gateway mirrors or reflector servers.
• Synchronous MCTs are used for "live broadcast events" (e.g., Victoria's Secret fashion shows) across the Internet (not the Web), using dedicated servers connected via Real-Time Streaming Protocols to purpose-built client programs (e.g., RealOne)
• Asynchronous MCTs are used to distribute large files across the Web using "mirror sites" to very large numbers of (download only) clients.
  

Configuration and Versions

• Configuration: An arrangement of components ("floorplan") whose interfaces and I/O resources are interconnected to other components using connectors.
• Version: An instance of a configuration, component or connector, with a unique interface

In search of a simple Enterprise System Architectural Description Language (ESADL)

• We want to develop and use an XML data description schema to describe enterprise system architectures in our team projects.
• XML data type definitions (or preferably XML data model schemas) can be sent/received over the Web
• This enables portable, reusable or mobile specification of System Architectures
•  xADL is an XML-based language for describing software system architectures, under development at UCI (Optional: reference materials).
• Want to learn more about xADL?
• Business Process Execution Language for Web Services (aka, "BPEL4WS") is the bleading edge version of such a language (not a product) from the folks at IBM, BEA Systems, Microsoft, Siebel Systems, and SAP AG.