Service Description And Dynamic Substitution Using Formal Method

With the rapid development of Internet technology and e-commerce, all kinds of enterprises have adopted the Web technology to move their main services into the internet to gain a broader perspective and make their service trade more automated and faster. SaaS (Software as a Service) is widely accepted and is considered to be the next important developing trend of software application. This trend will push the development of the technology of Web services. Now, Web services are playing a more and more important role in business activities and enterprise communication, so the stability of Web services has become the focus of attention. More and more research on the fault-tolerant technology of Web services is being done.Most of the traditional fault-tolerant technologies of Web services, which mainly consider from the aspect of service supplier and the service registry center, extend the standard protocols or the registry center and adopt the strategy of service redundancy for fault tolerance. But such fault-tolerant mechanisms are often transparent to the service consumer and can not make full use of the rich resource on the internet, therefore they lack of flexibility. This article proposes a fault-tolerant framework of Web services based on flow control method on behalf of the service consumer. This framework uses the functional matching strategy to dynamically find the backup service on the internet for each service in the active service flow. When some of the services in active service flow which is being run in the framework fail to responde, the failures are detected and the failed services are substituted by their backups, so the service flow can automatically resume operation quickly. The main research and innovative work are as follows:First, this article analyzes the traditional fault-tolerant technologies of Web services and lists their merits and demerits. Then a fault-tolerant framework based on multi-version service redundancy is proposed. The framework uses the Pull model to detect the Fail-stop failure. Once it detects a failure, it substitutes the failed service with the backup and keeps the service flow running.Second, information construction of the framework is analyzed. In fact, to build the information base of the framework is to describe the service's function. In our method, we use input, output and the internal logic process to clarify the function of the service formally and semantically. Domain Conception Ontology is used to describe the input and output. SOFL and Domain Process Ontology are introduced to describe the internal logic process. We give the form of service decription using SOFL and Domain Ontology (including Domain Conception Ontology and Domain Process Ontology).Third, based on the formal semantic description, we propose a three step matching method in which Domain Ontology matching, IO matching and Process matching are conducted successively to give out the high-precision matching result. Domain Ontology matching compares the Domain Conception Ontology and Domain Process Ontology between service request SR and service supplied SS. When SS refers all the Domain Ontologys which SR refers, they are matched on the Domain Ontology level. IO matching is essentially the matching of semantic information contained in the services'input and output. IO matching demands that the I/O of SS semantically contains the I/O of SR. Process matching compare the inner logic process of SS and SR. The inner logic process is described by the CDFD marked with Domain Process Ontology. Process Matching first converts each CDFD into a set of service-event chain, and calculate the similarity of the corresponding sets of SS and SR, this similarity is used to represent the matching degree.Fourth, we implement a prototype system, and use a typical sceen as an example to illustrate the feasibility and effectiveness of the framework. We mainly verify the service matching method and demonstrate it is effective and has high precision.