A Graph-based QoS-Aware Method for Web Service Composition with Branching

Abstract

The concept of Service-Oriented Architecture, where individual services can be combined to accomplish more complex tasks, provides a flexible and reusable approach to application development. Their composition can be performed manually, however doing so may prove to be challenging if many service alternatives with differing qualities are available. Evolutionary Computation (EC) techniques have been employed successfully to tackle this problem, especially Genetic Programming (GP), since it is capable of encoding conditional constraints on the composition's execution paths. While compositions can naturally be represented as Directed Acyclic Graphs (DAGs), GP needs to encode candidates as trees, which may pose conversion difficulties. To address that, this work proposes a Quality of Service (QoS)-aware EC composition approach that represents solutions directly as DAGs. This approach extends a previously proposed DAG representation by allowing it to also encode conditional constructs, thus producing solutions with multiple possible execution paths. The tree-based and graph-based composition approaches are compared, showing significant gains in execution time when using graphs.