Computational Complexity of Web Service Composition Based on Behavioral Descriptions

The Web Service Composition (WSC) problem on behav-ioral descriptions deals with the automatic construction of a coordinator web service to control a set of web services to reach the goal states. As such, WSC is one of the fundamen-tal techniques to enable the Service Oriented Architecture on the Web. Despite its importance and implications, how-ever, very few studies exist on the computational complexi-ties of the WSC problem. In this paper, we present two novel theoretical findings on WSC problems: (1) Solving the WSC problem with “complete ” information is EXP-hard, and (2) Solving the WSC problem with “incomplete ” information is 2-EXP-hard. These findings imply that more efforts to de-vise efficient approximate solutions to the WSC problem be needed. 1

On the Computational Complexity of Behavioral Description-Based Web Service Composition

The behavioral description-based Web Service Composition (WSC) problem deals with the automatic construction of a coordinator web service that controls a set of web services to reach the goal states. Despite its importance and implications, however, very few studies exist on the computational complexities of the WSC problem. In this paper, to address this problem, we present four novel theoretical findings on the WSC problem: (1) Solving the composition problem of deterministic web services for a restricted case (when the coordinator web service has complete information about the states of all web services) is PSPACE-hard, (2) Solving the composition problem of deterministic web services for a general case (when the coordinator web service has incomplete information about the states of web services) is EXPSPACE-hard, (3) Solving the composition problem of nondeterministic web services on complete information is EXP-hard, and (4) Solving the composition problem of non-deterministic web services on incomplete information (which is the most general case) is 2-EXP-hard. These findings suggest that more efforts to devise efficient approximation solutions to the WSC problem be needed

Type-Aware Web Service Composition Using Boolean Satisfiability Solver

The goal of the Web Service Composition (WSC) problem is to find an optimal “composition ” of web services to satisfy a given request using their syntactic and/or semantic features, when no single service satisfies it. In this paper, in particular, we study the WSC problem from semantic aspects, exploiting the supertype-subtype relationship among parameters, and propose a novel solution based on the boolean satisfiability problem (SAT). Given a set of web service descriptions and a requirement web service, we reduce the WSC problem into a reachability problem on a state-transition system, and show that the shortest path found is amount to the optimal composition. A preliminary experiment using 7 examples reveals that our proposal can find optimal compositions of web services efficiently. 1