An Extensible Directory Enabling Efficient Semantic Web Service Integration

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 service integration. The directory implementation relies on a compact numerical encoding of service parameters and on a multidimensional index structure. It supports isolated service integration sessions providing a consistent view of the directory data. During a session a client may issue multiple queries to the directory and retrieve the results incrementally. In order to optimize the interaction of the directory with different service composition algorithms, the directory supports custom ranking functions that are dynamically installed with the aid of mobile code. The 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 (e.g., denial-of-service attacks). With the aid of user-defined ranking functions, application-specific ordering heuristics can be deployed directly. Experiments on randomly generated problems show that they significantly reduce the number of query results that have to be transmitted to the client by up to 5 times.