Client-side Development with Axis

Chapter 8 • Web Services 297 http:www.cutter.comresearch2002edge020212.html http:www.computerworld.co.nznews.nsf0B289F477F155A539CC256DDE00631AF8?OpenDocument

8.7 Summary and Bibliographical Notes

SOAP is an XML-based communication protocol and encoding format for inter-application communication. SOAP provides technology for distributed object communication. Given the signature of a remote method Web service and the rules for invoking the method, SOAP allows for representing the remote method call in XML. SOAP supports loose-coupling of distributed applications that interact by exchanging one-way asynchronous messages among each other. SOAP is not aware of the semantics of the messages being exchanged through it. Any communication pattern, including request-response, has to be implemented by the applications that use SOAP for communication. The body of the SOAP message can contain any arbitrary XML content as the message payload. SOAP is widely viewed as the backbone to a new generation of cross-platform cross-language distributed computing applications, termed Web services. Service description plays a key role in a service-oriented architecture SOA in maintaining the loose coupling between the service customers and the service providers. Service description is a formal mechanism to unambiguously describe a Web service for the service customers. A Service description is involved in each of the three operations of SOA: publish, find and bind. In this chapter I reviewed the WSDL version 2.0 standard for describing Web services and how it is used to provide functional description of the Web services SOA model. There are other standards such as Web Services Flow Language WSDL and WSEL Web Services Endpoint Language which are used to describe the non functional aspects of Web services. The reader interested in these should consult the relevant Web sources. WSDL 2.0 is the current standard at the time of this writing. It is somewhat different from the previous version WSDL 1.1, and the interested reader may wish to consult [Dhesiaseelan, 2004] for details. Briefly, a reader familiar with WSDL 1.1 will notice that WSDL 2.0 does not have message elements. These are specified using the XML Schema type system in the types element. Also, portType element is renamed to interface and port is renamed to endpoint . Web Services Inspection Language WSILis a lightweight alternative to UDDI. The W3C website and recommendation documents for SOAP are at: http:www.w3.orgTRsoap . The latest is SOAP version 1.2 specification. This document has been produced by the XML Protocol Working Group, which is part of the Web Services Activity. Ivan Marsic • Rutgers University 298 http:soapuser.com WSDL at: http:www.w3.orgTRwsdl20 [Armstrong et al., 2005] A. Dhesiaseelan, “What’s new in WSDL 2.0,” published on XML.com, May 20, 2004. Available at: http:webservices.xml.comlptaws20040519wsdl2.html Problems Section 8.3 7.1 WSDL, although flexible, is rather complex and verbose. Suppose you will develop a set of Web services for a particular domain, e.g., travel arrangements. Define your own service language and then use XSLT to generate the WSDL. 7.2 Tbd