Research And Implementation Of HTN Based Service Composition Framework

The integration of enterprise applications has become a trend with thedevelopment of SOA (Service-Oriented Architecture) and new functionscan be developed easily by compositing existing Web Services. But withthe growing number of Web Services, manual service composition isbecoming more and more difficult. What’s more, A Web services can bepublished on any platform, be developed by any language, which leads tocomplex and changing environment contexts in a Web service basedsystem. So how to perform an automatic Web Service Composition whichsupports quickly service discovery and dynamic environment contextmanagement has become a research focus.This paper proposed an automatic Web Service compositionframework to solve these problems. The framework uses an ontologybased Web service description which is an extension of OWL-S. Thedescription involves service domain and service context, which supportsdynamic integrations of services. The framework also includes automaticservice composition by using HTN (Hierarchical Task Network) planning.Finally, the requester can choose context constrains of each Web service inthe execution sequence, then the system can dynamically replace servicewhich does not meet the constrain of service context during serviceexecution process.The main contributions of this paper are:1. Proposed an improved semantic model of Web service, whichinclude two parts: functional service and context service. The functional service is used to achieve functional requirements ofWeb service, and the context service is used to get environmentcontext information of Web service.2. Achieve service integration by using K-Means algorithm, and givesan improvement of the algorithm which solves the problems suchas choosing initial integration centers of K-Means. Based on theintegration algorithm, this paper proposed a two stage Web servicematch-making algorithm which greatly improved service matchingefficiency.3. Achieve dynamic context type discovering by integrating contextservices of Web Services. When a Web service’s context can’t meetthe context constrain, the integration result supports quicklyselecting replaceable service which has the same environmentcontext type.4. On the basis of researches above, an automatic Web servicecomposition framework was designed and implemented. Theframework was based on service integration, and used HTNplanning as dynamic planning algorithm. The framework also usedservice integration to improve planning and execution process ofWeb services. What’s more, the framework can monitorenvironment changes during service execution, and dynamicallychoose replaceable service which can satisfy the context constrains.By doing this, the framework achieved self-adaptive duringexecution process.