Redundant Service Removal in QoS-Aware Service Composition

Abstract

QoS-aware service composition is the generation of a business process to fulfill functional goals and optimize the QoS criteria at the same time. People may focus on the optimization of a single QoS criterion or a set of QoS criteria. We find that though many composition algorithms can get the optimal QoS values, the solutions obtained can possibly contain redundant services, the removal of which does not worsen the QoS value of the solution. In the literatures using Web Service Challenge (WSC) open data sets, the removable services can be over 30% of the services in the solutions. This common problem has been ignored so far. The fundamental reason is that execution cost is not one of the criteria to optimize. Even in the cases when execution costs are not explicitly given for each service, we are still motivated to reduce the number of services in the final solution by assuming each service takes unit cost. In this paper, we study the redundancy removal problem to further optimize the QoS optimal solutions obtained by QoS-aware service composition algorithms. We model the redundancy removal problem as an integer programming problem. Though solvable using a standard solver, we present an algorithm to solve the problem in this specific context and it proves to have better performance than a standard integer programming solver. We also present the results of our data experiments.

Automated Web Service Composition Algorithm Based on Improved Planning Graph

“…Most proposed formal definitions of Web services, such as those appearing in [5,6,32,13,16,30] consider the service as a stateless black box (no conversations) that receives an input message and generates an output message. In the ASC problem, it is more practical to assume that services are stateless rather than stateful processes (i.e., that have an internal behavior).…”

“…For the description of Web services, the standard WSDL (Web Services Description Language) [27] often used, which only provides a description of the functionality given by the service. To that end, we can add semantic information to the description of the service inputs and outputs by using OWL [28] as used in many work including [5]. For the description of the quality of services, the WSLA language [11] can be employed; that is the case in the data sets used in the evaluation section (Section 4).…”

“…To render the figure more illustrative, we present the no-op actions only in the first layer; as well, we do not draw the input/output arcs connecting the actions that are repeated in previous layers (the shaded actions in Figure 2). In the propositions state of Layer 2, the goal set {G, K} is included, which indicates the existence of a solution, e.g., (w 1 ; w 5 || w 6 ), w 1 followed by w 5 and w 6 in parallel. …”

“…The adding of these propositions is to keep the paths of all possible solutions, in the minimal planning graph. 5 The minimization of planning graph is polynomial in the size of the planning problem.…”

Scaling Up Web Service Composition with the Skyline Operator

“…The Graphplan approach constructs a planning graph and returns a solution in a short time. However, the solution returned is not the optimal one and may contain redundant services (a service is redundant if all its outputs used by other services are also produced by other services [8]). 2) Finally, a database approach relies on pre-computed service combinations stored in a relational database.…”