A Study On Technologies Of Web Service Composition Oriented QoS Evaluation

Web Services are independent, modelizational applied programs self-contained, modular applications that can be described, published, located, and invoked over a network. Services composition achieve more powerful business functions by combining existed web services dynamically and offer unprecedented opportunities for different business integrations in enterprises. As the number of web service increases, it's getting hotter and hotter on how to select a group of web services among a mass of candidates with the same function so that the composite web service can achieve a fine quality of performance. Moreover, the service selection is dependent on the evaluation of composition services QoS model directly, so it becomes one of the urgent problems to construct a proper QoS model according to the individuation desire of different users for each task in the business flow, in order to select a group of more satisfied services.Non-functional properties describe the executive feature (e.g. execution time, reliability, availability and security etc) which will be shown in the process of completing the function by the Web Services, and the executive feature value influences the quality of service (QoS) directly. In general, people use the QoS cretiria to represent the ones of non-functional properties processed by separation, merge and quantization, and to indicate quantitatively good or not about the Web Services quality with the QoS. From above, we can see that the researches on Non-functional properties of Web services are the foundation of QoS evaluation. And this paper starts from such features as evaluation subjectivity, business relativality, dependency and uncertainty which are belong to Non-functional properties of Web services.There are many evaluation criteria on QoS, so multiattribute synthesis evaluation theories commonly offer each criterion a weight value, and then treat many criteria values as a single value. QoS model formally includes QoS cretiria and different cretiria weight values, therefore, we emphasis on uncertainty disposal of QoS evaluation, dependency analysis and the strong relationship between QoS cretiria ang their weights. Moreover, we provide a few of methods for QoS evaluation of Web services, which support services selection aiming at essential problems in QoS evaluation. Of Web servicesWeb services composition is a series of Web services which can both be the final application and be a new Web service. In practice, the execution sequence of different Web services and the complex interaction of Web services determine the composition. In general, only composite services can meet the users'requirement. Therefore, the paper supports individuation QoS evaluation method facing to the business functional constraints and relativity feebleness, and in fact, the method is a QoS evaluation model aiming at basic services in order to deliminite the rigidification of consistency of QoS evaluation, furthermore, and then builds up the composition services QoS evaluation model(orienting to composition services bussiness) integrated by individuation QoS compostion. We completed such works as following:(1) Aiming at uncertainty of non-functional properties of Web services, we research the uncertainty classification, and devide uncertainty of evaluation criteria of Web services with uncertainty of QoS criteria and uncertainty of criteria weights, therinto, and the former can be parted by uncertainty of description and behavior; and the latter can be separated by uncertainty of subjectivity and objectivity. And we provide a processing way for description uncertainty of QoS criteria based on fuzzy sets, a processing method for behavior uncertainty of QoS criteria based on grey forecasting, and a processing approach on subjectivity weight based on AHP.(2) Aiming at relativity of non-functional properties of Web services, we research the relativity classification, and devide relativity of evaluation criteria of Web services with relativity of QoS criteria themselves and relativity of QoS criteria and constraints of non-functional properties of Web services. Moreover, we support an analysis way for the relativity of QoS criteria of Web services based on grey relational analysis,and an analysis method for relativity of QoS criteria of Web services and constraints of non-functional properties based on connection-number and set-pair shi.(3) Aiming at features that there is not character weighted information, but only connection-number weight information in set pair analysis, we research the character weighted in set pair analysis, and bring up a character weighted set pair analysis way supporting services selection, which can turn the relativity of QoS criteria and constraints of non-functional properties of Web services into more acute.(4) Aiming at such sensitive problems as weighted sum and QoS evaluation method, we provide QoS non-weighted evaluation approach which supporing services selection, that is directly compare the relational degree between QoS criteria of Web services and constraints of non-functional properties of Web service, which can eliminate the confusion about weights and abtain the results from objective data straightly. (5) Aiming at such uncared-for problems as QoS of Web services working on non-critical tasks in composition flow, we research on a method for indetifying critical route and acquiring non-critical task in parallel structure, the relationship between dependency and relative criteria, and provide the QoS evaluation approach orienting to non-critical task in parallel structure with single goal satisfication and multi-goals optimizationy.(6) Aiming at such features as subjectivity of evaluation of non-functional properties, business relativity, dependency and uncertainty which are not considered completely in Web services, we provide that individuation QoS evaluation model of Web services orienting to business functions constraints and dependency weakening, and which is the foundation of the compositon services QoS model combined by individuation QoS of basic services of Web services orienting to compositon business.