Services

Web Services

There are many definitions (or beliefs) of what a "web service" is which, as with other definitions and semantics, change with context and time. For example, didnt we have web services when the browser and HTML was born?

Ok, from the systems integration view of web services, my preference is to take the W3C Web Services Requirements definition (being the World Wide WEB consortium) which is:

“A web service is a software application identified by a URI, whose interfaces and binding are capable of being defined, described and discovered by XML artefacts and supports direct interactions with other software applications using XML based messages via Internet-based protocols.”

Infact, even the W3C give differing definitions (W3C Web Services Architecture Group)… but I believe the above definition is flexible enough to cater for different technologies and transport protocols.

Whilst Web Services themselves are components with a clearly defined interface, the architecture lacks verification and validation of process behaviour in the composition and coordination of these services to the requirements and behaviour of users (or clients) of these services. This is in a similar way to that of analysing the impact of customisation and personalisation of web sites, in which the main problems associated with reusable web sites is that they are written without significant analysis of the potential use-cases and the needs of various clients (Bonett 2001). We describe what constitutes a web service’s behaviour as; “A web service’s behaviour is defined by the set of activities behind that service and mapping those activities to message exchanges.”

Web Service behaviour

Web Service behaviour analysis consists of analysing two aspects of web service architecture style. The web service formally exhibits its identity and permissible interactions through definition in the Web Service Description Language (WSDL). However, within the implementation for a web service the behaviour of its interactions is defined. The coordination of a service’s behaviour is formed from the basic operations of service invocation, replying to a service or receiving the reply from a service and this forms the basis for service analysis for its interaction behaviour. Standards elaborate the specification of how, what and when these interactions can occur.

In essence, to analyse web services we must consider what is defined by and behind the service interface, and consider those activities that comprise the process that the service offers. Web Service Behaviour Analysis can be described as; “Web Service Behaviour Analysis considers analysing the set of activities behind a service (a composition), and together with service interactions (choreography), provides an end-to-end view that models the role of each individual process in the choreography and the activities performed by each role.” The theme of Web Service behaviour is used throughout our work, and is the basis for understanding what may be observable from a web service implementation and a partnered composition process. The behaviour aspect of web services also encourages a view of the problem domain for the web services architecture.

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