A new services-oriented view of infrastructure is required to ensure a successful long-term transition to effective Web services for the enterprise, according to META Group, who sees web services as essentially another (better) attempt at deploying and linking applications using open standards. Web services basically represents a shift from a component-oriented to a service-oriented infrastructure architecture. The analysts predicts that web services will be significantly deployed first within the internal enterprise during 2002 and 2003, and from 2004 between enterprises. During 2002 and 2003, organisations will begin experimenting with elements of Web services, attempting to identify critical infrastructure issues and assessing the networkability of applications developed in those environments. As Web services mature, from 2004 to 2006, application networkability assessments (ANAs) will increasingly be used to rate both purchased Web services solutions and outsourced Web services. After 2007, a unified Web services network architecture will share a standard access method to those services.
The clue: viewing infrastructure as a collection of components and patterns will expand to include application, technical, and operational services concepts. For Web services, the unit of composition is not defined via an application programming interface, but as a pattern of interactions between providers and subscribers and the information exchanged during those
interactions (i.e., protocols and formats).
W3C’s Web Services Architecture Working Group has published a Working Draft of 14 November 2002 where they define a web service as follows:
A Web service is a software system identified by a URI, whose public
interfaces and bindings are defined and described using XML. Its definition
can be discovered by other software systems. These systems may then interact
with the Web service in a manner prescribed by its definition, using XML
based messages conveyed by internet protocols
Eric van der Vlist recently wrote an article, SOAP Web Services: built on a contradiction?, where he argues that the RPC approach which is one of the selling points of SOAP can’t be called loosely coupled, and that the infrastructure needs to be totally refactored to be suited for Web Services. ::Manageability:: has a nice comparison between the old and the new:
| Tight Coupling | Loose Coupling | |
| Interface | Class and Methods | REST like (i.e. fixed verbs) |
| Messaging | Procedure Call | Document Passing |
| Typing | Static | Dynamic |
| Synchronization | Synchronous | Asynchronous |
| References | Named | Queried |
| Ontology (Interpretation) | By Prior Agreement | Self Describing (On The Fly) |
| Schema | Grammar Based | Pattern Based |
| Communication | Point to Point | Multicast |
| Interaction | Direct | Brokered |
| Evaluation (Sequencing) | Eager | Lazy |
| Motivation | Correctness, Efficiency | Adaptability, Interoperability |
And concludes: “[I]f the goal is to achieve better interoperability then we need to deviate from the familiar and be prepared to make some hard choices.”
