AND/OR directed graph for dynamic web service composition

Abstract

Nowadays, web services have become more popular and are the most preferred technology for distributed system development. However, several issues related to the dynamic nature of the web still need to be addressed, such as scalability, high complexity, high computing costs and failure issues. It becomes very important to find efficient solutions for the composition of web services, capable of handling different problems such as large quantities of services, semantics or user’s constraints. In this chapter, we formalize the web Service composition problem as a search problem in an AND/OR Service Dependency Graph, where nodes represent available services and arcs represent the semantic input/output dependencies among these services. A set of dynamic optimization techniques based on redundancy analysis and service dominance has been included to reduce the size of this graph and thus improves the scalability and performance of our approach. We pre-calculate all the shortest paths between each pair of this graph’s node using a graph search algorithm. These paths will be used upon the receipt of a client request. The construction of the graph and calculation of the shortest paths are done offline to remove this time-consuming task from the composition search process; therefore optimizing the composition process by reducing the computational effort when running the query. Furthermore, in addition to the sequence and fork relations, our model supports the parallel relation.