Web service

Draft

Definition

According to Wikipedia (retrieved 20:22, 23 April 2007 (MEST)), the W3C defines a Web service as a software system designed to support interoperable Machine to Machine interaction over a network. Web services are frequently just Web APIs that can be accessed over a network, such as the Internet, and executed on a remote system hosting the requested services.

A Web service is any piece of software that makes itself available over the Internet and uses a standardized XML messaging system. (Top Ten FAQs for Web Services, retrieved 20:22, 23 April 2007 (MEST)

Web services stack components

The Web service protocol stack is an evolving set of protocols used to define, discover, and implement Web services. The core protocol stack consists of four layers:

• Transport: E.g. HTTP, SMTP, FTP, and newer protocols.
• XML messaging: E.g. Simple Object Access Protocol (SOAP) or XML-RPC. These define messages containing a service request and a response. SOAP and XML-RPC etc. are independent of any particular transport and implementation technology.
• Service description: E.g. Web Services Description Language (WSDL) - describes what a service does in a machine readable way
• Service discovery: E.g. Universal Discovery, Description, Integration (UDDI) - a service to publish available services

List of standards (in ascending order)

• Common Internet protocols (e.g. TCP/IP, HTTP)
• XML, the formalism
• Simple Object Access Protocol (SOAP) 1.1, W3C note. "SOAP is a lightweight protocol for exchange of information in a decentralized, distributed environment. It is an XML based protocol that consists of three parts: an envelope that defines a framework for describing what is in a message and how to process it, a set of encoding rules for expressing instances of application-defined datatypes, and a convention for representing remote procedure calls and responses". Note DKS: This is generally the lowest Service Layer (just on top of HTTP) and tells how to describe messages that are sent or received.
• Web Services Description Language (WSDL), W3C Note. WSDL is an XML format for describing network services as a set of endpoints (methodes/calls) operating on messages containing either document-oriented or procedure-oriented information.
• UDDI (Universal Description, Discovery and Integration) enables organizations to (I) discover each other by a directory of service providers and services, and (II) find out what services are available
• WSFL (Web Services Flow Language) article from IBM. WSFL is an XML language (compatible with SOAP, UDDI & WSDL) for the description of the overall process logic of Web Services. See also [Business processes and workflow in the Web services world and ]Cover Pages about his
• Apache references to the WSIF (Web Services Invocation Framework) . This is a description of APIs to invoke Web Services described in WSDL. (Can, but does not need to be built on top of SOAP).
• WSIL (Web Services Inspection Language) WS-Inspection specification provides an XML format for assisting in the inspection of a site for available services and a set of rules for how inspection related information should be made available for consumption (IBM/Microsoft)
• WSRP (Web Services for Remote Portals): XML and Web services standard that will allow the plug-n-play of visual, user-facing Web services with portals or other intermediary Web applications. (Oasis led initiative)
• ebXML Messaging Service Specification (OASIS led) provides a secure method for exchanging electronic business transactions using the Internet. (This is a rather big project with several sub-specifications). See D. Mertz "Understanding ebXML" at developerworks/IBM.

... There are lots of WS-standards down the pipeline ...

Webservices in education

Rehak et al. model

“The era of monolithic Learning Technology Systems is over. Rather than building large, closed systems, the current focus is on flexible architectures that provide interoperability of components and learning content, and that rely on open standards for information exchange and component integration. The Learning Systems Architecture Lab has developed the concept of a Learning Services Architecture and the Learning Services Stack as a framework for developing the next generation of learning technology systems. We're in the process of developing learning services using Web services and Web services technologies.” (http://lsal.org/, retrieved 20:22, 23 April 2007 (MEST)).

The stack according to Rehal et al. has three fundamental layers:

• User agents: Authoring, delivery, management
• Learning services: At its heart there are knowledge and content mangement, user profile and tracking, sequencing. On top of this are various tools for interaction, presentation, lectureing, assessment, simulation, collaboration, etc.
• Infrastructure: Lower level protocols (e.g. HTTP), transport (e.g. SOAP), discovery (e.g. UDDI), description (WSDL), workflow (WSFL)

It may look like this:

( HTTP -> ) SOAP -> UDDI -> WSDL | WSIF ? -> WSFL ? -> -> ebXML? | WSIL ? -> WSRP? -> Portal

A social software model ?

Daniel K. Schneider wonders how one could conceptualize integration of various social software (e.g. blogs, wikis, reference management, etc.) as webservices into a portal.

Players

There are many players in this field

• The Web Services Activity Statement and the Web Services Activity give an overview of the W3's idea on application to application communication (web services). See also: Web Services Description Requirements and the Web Services Glossary.
• Oasis is an other organization working on xml-based e-business standards
• "What's Next: The Future of Web Services" from Microsoft
• XMethods has a long list of publicly available web services , implementations, tutorials, etc.

In educational technology

• Learning Systems Architecture Lab

Links

Standards and recommendations

• Web Services Architecture (W3C Working Group Note 11 February 2004)

For education

• Dig around in the lsal.org papers and presentations
• The infamous learning services stack diagram PDF

Other

• Build a Web Service Analyzer using XSLT (400 KB>, Ammai.com tutorial
• Sun's XML page has a lot of information concerning concerning Java-based webservices. (3/2003)
• Why Use SOAP? Choosing Between SOAP and Application-Specific XML for Your Web Services by Frank Sommers, March 17, 2003 (artima.com)

References

• Blackmon, William H. and Daniel R. Rehak (2003). Customized Learning: A Web Services Approach HTML, Proceedings: Ed-Media 2003, June 2003. HTML - PDF (available from http://lsal.org/lsal/expertise/papers/).

• Wilson, Scott; Kerry Blinco and Daniel Rehak (2004). An e-Learning Framework: A Summary, alt-i-lab 2004:Advancing Learning Technology Interoperability, PDF