A Directory for Web Service Integration Supporting Custom Query Pruning and Ranking

In an open environment populated by large numbers of heterogeneous information services, integration is a major challenge. In such a setting, the efficient coupling between directory-based service discovery and service composition engines is crucial. In this paper we present a directory service that offers specific functionality in order to enable efficient web service integration. Results matching with a directory query are retrieved incrementally on demand, whenever the service composition engine needs new results. In order to optimize the interaction of the directory with different service composition algorithms, the directory supports custom pruning and ranking functions that are dynamically installed with the aid of mobile code. The pruning and ranking functions are written in Java, but the directory service imposes severe restrictions on the programming model in order to protect itself against malicious or erroneous code. With the aid of user-defined pruning and ranking functions, application-specific ordering heuristics can be directly installed into the directory. Due to its extensibility, the directory can be tailored to the needs of various service integration algorithms. This is crucial, as service composition still needs a lot of research and experimentation in order to develop industrial-strength algorithms. Experiments on randomly generated problems show that special pruning and ranking functions significantly reduce the number of query results that have to be transmitted to the client by up to 5 times.