Web Service Discovery Processing Steps

The most straightforward but also most inflexible configuration approach for invocation of remote services is to hard wire the location, interface, behavior and other properties of remote services into the local application. Loosely coupled decentralized systems call for solutions that are more flexible and can seamlessly adapt to changing conditions. While advances have recently been made in the field of web service specification, invocation and registration, the problem has so far received little systematic conceptual attention. In this paper, we outline seven web service problem areas and their associated processing steps, namely description, presentation, publication, request, discovery, brokering and execution. We propose a simple grammar (SWSDL) for describing network services as collections of service interfaces capable of executing operations over network protocols to endpoints. A service must present its current (up-to-date) description so that clients from anywhere can retrieve it at any time. A registry for publication and query of service and resource presence information is outlined. Reliable, predictable and simple distributed registry state maintenance in the presence of service failure, misbehavior or change is addressed by a simple and effective soft state mechanism. The notions of request, resource and operation are clarified. We outline the discovery step, which finds services implementing the operations required by a request. The brokering step determines an invocation schedule, which is a mapping over time of unbound operations to service operation invocations using given resources. Finally, the execution step implements a schedule, by using the supported protocols to invoke operations on remote services.