The Critical Technologies Based On QoS Dynamic Web Services Composition

With the rapid development of Web Services technology and its application in recent years,more and more stable and easy to use Web Services are shared on the Internet. The quantity of similar Web Services grows fast, and web services composition technology develops continually, then the number of services with the same or similar service functions has increased, therefore, the utilization of QoS (quality of service) in selecting services has become the key technologies in practical use of dynamic Web Service composition.At present, a lot of work has been done in the domain of Web Services composition based on QoS by many scholars from home and abroad, however, there are some new problems existing at the same time. For example, there is no a standard QoS model that is authorized widely, which leads to a great variety of models existing and the correctness and reasonableness of some models among them are still to be tested. In the existing QoS model, the property value (weights) of candidate service is set by users, who may not know the service in this area and just pursue the low price of the service. Consequently, according to this weight setting way, the service selected at last may not be the most appropriate one, which impacts the selection of the candidate service during the service composition. In addition, the selection algorithms of Web Service based on the QoS, to a large extent, mainly use the mathematics optimization theory as a source of reference. The researchers neither consider the selecting strategies of the Web service composition, nor excavate the characteristics of the Web services composition.Accordingly, in order to solve the above problems, based on the study of the basic properties of existing QoS model of Web services, this paper introduces a new QoS attributes-Compositionality and a key attribute of the QoS properties, gives the definition and calculation formula of them, and forms a new QoS model. On this basis, according to description on the services selection of Zeng'paper, presents a strategy and algorithm of the services selection, which aims to confront the condition when the number of services of the candidate web services set is large. Add a sort algorithm and a segment function, select the services, the QoS properties value of which is high, and reduce the number of the candidate web services set. Through the comparison and analysis among the imitation experiments, this method is more conducive to select the single service of the composition services. It solved the problem that the value of Service QoS property is arbitrary set by users, leading to the improper candidate service selected in web service composition. Moreover, on the premise of the successful rate of service composition, this strategy improved the efficiency of the web service composition.