The Big Picture
Earlier, component technologies such as DCOM, Corba, and EJB tried extending the client/server application integration to Web-enabled components, but failed due to the absence of standards such as native handling of RPC. And this is the space that Web services is trying to address with the following components
XML: Default standard for data format and exchange
SOAP: Protocol for application communication
WDSL: Format for describing Web services
UDDI: Yellow Pages for finding Web services
The way it works in a real-life scenario is that if as an enterprise you have published an application as a Web service for use by other businesses, you begin by defining an interface to your application using WSDL (Web Services Description Language). The next step is Universal Description, Discovery, and Integration, in which the resulting API, along with application details, is published to a UDDI (Universal) Registry for classification and need-based search. In the above process flow, SOAP (Simple Object Access Protocol) is used for communication (like an envelope is used in postal mail).
Most developers would agree that the Web services model is fast becoming another attempt at vendor-pushed standards with blatant disregard for technological issues such as open standard, platform independence, and interoperatability. This is particularly visible because most vendors are first building standards internally and then submitting them to the W3C for standardization. However, the good news is that OASIS has agreed to support Biztalk Framework, thus eliminating the need for an adaptor to talk to the standards.
As XML-based messaging technologies become more or less standardized for the enterprises lost in the myriad of offerings (such as SOAP, UDDI, WSDL, ebXML, DISCO), technological choices are clearly strategic, depending only on the level of integration required (remember that they will not replace integration brokers). As more and more industries build XML vocabularies based on their business requirements, the need to have standardized data-delivery mechanisms (XML messaging protocols) will become far greater than ever before.
(Bhavish Sood is a strategist with Plexus Technologies. Write to him at email@example.com.)