Abstract:

At first glance, it appears that Web services ought to be described in a "context-free" manner.  After all, a Web service is normally conceived as a neatly encapsulated module of functionality that can be easily reused, so long as the inputs, outputs, and messaging protocol are conformant with its description.  However, when we look beyond toy examples, we see that the picture is not nearly so simple.  To support automated discovery and selection of world-changing services, for example, service descriptions must be unambiguous about what situations will guarantee successful service uses, and what new situations will result from those uses.  For some categories of services, service behavior may vary with time, location, user history, pre-existing contractual commitments, and so forth; descriptions of such distinctions can quickly become complex.

Moreover, many aspects of service use and management may require knowledge that isn't normally captured in service descriptions. Matchmakers may want to consider provider track records, reputation, and recommendations from third parties.   Service compositions, to be effective, may need to consider a variety of resource constraints and interrelationships between service providers.  Recovery from failure may involve a complex set of factors including user preferences, account status, policies that vary for different kinds of transactions, availability of appropriate substitutes (items or actions), etc.

Indeed, when considering the full range of service-related activities, it becomes clear that dealing with context is a major challenge, requiring far greater expressiveness and reasoning capabilities than are supported by the current widely accepted building blocks of the Web services stack.

This talk will focus on Semantic Web services technology and the mechanisms it provides to deal with context.  In addition to giving an overview of work on Semantic Web services, I will consider what kinds of contextual knowledge Web service-based systems need to handle, show how selected Semantic Web services approaches might be applied to these challenges, and speculate about what else might be needed.