Research On Dynamic Combination Method Of Railway Information Web Service Based On QoS

With the continuous development of China railway information for these years, therailway information construction in China for long-term progress and development. Therailway information construction has made a great achievement in the three main fields of thetransportation organization, passenger and cargo marketing and business management.However, for some development reasons, existing business information systems based on theoriginal information architecture, each take its separate application as its center, so forming a“chimney type” layout in whole railway field, thus the exchange of sharing informationencountered more obstacles. The railway information system has to integrated the businesssystems to improve overall coordination and comprehensive benefits. Change this situation assoon as possible has become an urgent problem in the construction of railway information.Railway information sharing platform to achieve interoperability, information sharing,interaction and coordination, integrated application has become a consensus, is also one of thekey research in the field of information areas in recent years.With the development of service-oriented architecture SOA, the new solution isproposed for heterogeneous information sharing and comprehensive information utilization.To build a railway information platform is the solution to solve railway information sharingproblem. Service-oriented architecture SOA permits users calling on different services inSOA. The applications and components are packaged into “web service” in businessinformation systems. The function unit of application is providing unified interface. More andmore railway business information systems publish web service, such as ComprehensiveMonitoring System of Train Operating Safety. CMSTOS contains a lot of heterogeneoussub-systems and dealing with various businesses. CMSTOS needs to sharing the informationwith Truck Performance Detecting System, The infrared hotbox detection system, The statemonitoring system of freight train loading(safety gate), Sway car instrument. Traindispatching command system has to share the information with plan, China RailwayHigh-Speed/rolling stock, Power system, maintenance, Passenger dispatching informationsystem.More and more applications and components packaged into Web services are used byother systems. The chiefly problem is how to compose the same function web services.Choosing a best service from numerous services is becoming a hotspot.This thesis takes the sharing of railway information background as reference;Particularly, it has proposed architecture to automatically select and replace web service basedon the QoS parameters in dynamic environment and also simulate and verify its reliability,which is suit for practical use. This thesis has mainly contributed in five aspects:Firstly, this thesis presented an approach to estimate probability distribution of serviceQoS in the case of small number of sample.Using max entropy principle, the analyticalformula of the probability density function can be obtained by transforming the probabilitydistribution estimate problem.Then It use an algorithm to estimate parameters of theprobability density function was designed．It set partially parameters as random variable tocompute the globle QoS formula, and applied statistical method to estimate QoS value.Then，Based on the fuzzy AHP method to calculate the subjective weight, Euclideandistance is used to calculate the objective weight, finally gives a combination of subjectiveand objective weight are integrated weight more scientific and more applicable to the user.Thirdly, this thesis improve a genetic algorithm based on the decimal float encoding tooptimize the QoS web service composition, and use the generalized table structure encodingto increase the accuracy and complexity of the proposed algorithm.It improve the crossoverstrategy and Golden selection method.Fourthly, proposed an algorithm to replace the service choice based on the QoSoptimization under the condition semi-automatic combination with static combination anddynamic binding.Lastly, according to the system of the railway information sharing, design a railwayinformation service agent platform to implement the above algorithms. Under the premise ofnot existing third-party web services to modify the service agent, full realization of theproposed combination of dynamic QoS-based Web services from obtaining QoS indicators toreplace a series of process.