Semantic Web Service Composition Supports If-Then-Else Structure

To achieve complex applications, the inhomogeneous semantic web services on Internet are required to cooperate. Current researches on web services composition are mostly limited to the composition for sequence structures. These simple one-dimensional linear composition approaches cannot meet the demands of more complex applications and more complex implementation environments. This article focuses on the research of semantic web services composition supports if-then-else structure. With if-then-else control construct, the result of this composition approach is a directed graph. The composite web service results from the composition can execute in conditions where some component services have nondeterministic effects, and the environments are totally observable.To support the composition with if-then-else structure for semantic web services, this article extends the graphplan. The classic graphplan succeeded for its soundness, completeness and high efficiency. But the classic graphplan is limited to STRIPS-like domain description, and can only generate linear structural plan solutions. The graphplan extension of this article, named combining-graphplan, can deal with actions with nondeterministic effects, and generate tree-like solutions. The main idea of combining-graphplan is splitting the nondeterministic action to multiple actions, and extending the plan graph to some adequate level, extracting all action sequences which can reach the goal, and then combining these sequences which deal with the different effects of nondeterministic actions, to solution tree. The combining-graphplan algorithm is simple, and only generates one plan graph during the plan process, and will not make the time complexity increase exponentially. Combining-graphplan is sound, and can easily be modify to have the important feature of completeness.The author's some endeavor is try to make the web services composition tool, i.e., OntoComposer mentioned in the article, be more simple and easy to use. Compare with other composers, OntoComposer has these characteristics: 1) Compose at the domain layer, the user cannot see the implementation technology of web services and OWL-S language; 2) Visualizably edit problems and compose services, there is no need to programming during the composition process; 3) Automatic composition cooperates with manual composition.