Research On Key Technologies Of Web Service Adaptation

Service-oriented software application is one of the important trends in the field of software engineering.The Web service-based distributed computing paradigm “Service-Oriented Computing” is the most important mark of service-oriented software applications.It treats service as the basic unit for building software,and hopes to maximally utilize and share the network software resources through unified technical specifications.However,current Web services are often developed by many different institutes,which leads to extensive heterogeneity in the interface description languages,functional implementations and runtime behaviors.Although the standardization of Web service description languages reduces the heterogeneity,it does not completely eliminate the heterogeneity.Consequently,these Web services have very low reusability,and obstruct the popularization of Service-Oriented Computing.Thus,how to overcome the heterogeneity of Web services,how to improve the correctness and robustness of collaborations among Web services become the crucial problem of carrying out Service-Oriented software applications.Web service adaptation is necessarily raised as the feasible solution to solve the above problems as well as the key technology to the popularization of Service-Orented software applications.Web service adaptation stems from software adaptation,and it is the continuation and development of software adaptation.Before the advent of Web service adaptation,software adaptation primarily provides solutions for the problem of small-scale software reuse in a very small range.After the proposal of Web service adaptation,software adaptation concerns mainly on Web service adaptation,primarily providing correctly and robustly collaborative solutions for the problem of large-scaleenterprise business integration of network software resources in a very wide range.Faced with distributed,heterogeneouspre-existing services(commonly denominated commercial-off-the-shelf),how to mediate themto build new business applications has become a hotspot problem of software engineering.With the above requirementsbeing the research background,we have investigated some important issues of service adaptation.The contributions of this dissertation are as follows:(1)Formal Model of Web servicesWeb service description can be divided into four levels: signature,behavior,semantic and quality.In this dissertation,based on the analysis of existing formalisms of Web services,we present a Hierarchical and Extensible Service Model HESM which abstracts signature and behavior level information of services.The signature describes the basic information of service interface,includingmessages,message types and actions(or operations).The behavior characterizes the interaction of services by Labeled Transition Systems,Service Flow Nets,or PI Calculus.LTS can intuitively describe the interaction of services with states and transition relations;SFNs can intuitively describe control and data dependencies among interface actions and messages;PI Calculus can characterize services with strutctural changes at runtime.Besides,SFN and PI Calculus both can be equipped with a labeledtransition system semantics,therefore,service behavior with the above formalisms can be equivalently transformed into LTS representations.HESM extended with ontology semantic descriptions can characterize semantics of Web service interfaces.HESM extended with security attributes can characterize the security requirements of Web services.HESM takesinto account various factors which affect Web service interactions.It supports accurate description and analysis of Web services by hierarchical descriptions,extended descriptions and several behavior representations,which provide a solid formal basis for the solution of the key technical problems of Web service adaptation.(2)Service adaptability analysis methodService adaptation cannot guarantee to solve all mismatches,and there are always risks that service adaptation may fail.Faced with this problem,this dissertation proposes the concept of service adaptability and the methods for service adaptability analysis.Service adaptability analysis checks whether there exists adapters capable of mediating incompatible services in order to achieve correct interactions.The adaptability analysis method based on the reachability graph of the composition of Service Flow Nets may result in state explosion issues when the size of service rises.This dissertation proposes ananalysis method based on the reachability graph of component Service Flow Nets.This method generates a reachability graph for each Service Flow Net based on action mappings of component services,and it determines the adaptability by checking the state nodes of component reachability graphs.Through the algorithm and case analysis,the article shows thatthis method can effectively save space overhead and avoid state space explosion problems.(3)Ontology-based generation ofservice interface action mappingsInterface action mappings,as a kind of simple and widely usedadapter specifications,occupy an important position in service adaptation.The design of interface action mappings is mainly a manual error-prone task which obliges the designer to have a full understanding of all service details.Type-based generation of interface action mappingshas low accuracy and will produce a large number of incorrect interface action mappings.Furthermore,we lack of effective verification methods towards these generations.Faced with these problems,this dissertation extends HESM with ontology semantics,proposes an ontology-based method forthe generation of service interface action mappings.This method is not only to automatically building interface action mappings,but also can achieve good accuracy.On this basis,we propose to verify the correctness of interface action mappings through checking data dependencies and analyzing behavior adaptability.This method is of great value to the development of automatic Web service adaptation.(4)Product of LTS-based service behavior adaptationThis dissertation proposes an adapter generation method based on simulation broadcast product of labeled transition systems,and an adapter verification method based on interaction product of labeled transition systems.The effectiveness of them is verified together with examples.These methods are based onthe product of LTSs to generate and verify the behavior adapter,which is a fullyautomaticderivation process.The most important characteristic of these methods is the transformation of interface action mappings into labeled transition systems,in which the dependencies among interface actions are represented by transition relations.Meanwhile,the method supports multiple Web service adaptation by generating a unique adapter.Therefore,this contribution has great value for who studies automatic behavior adaptation using formal methods and large-scale Web Service Adaptation.(5)Methods for dynamic service adaptationSince static service adaptation is difficult to support service evolution and updates,this dissertation presents a mechanism for dynamic service adaptation.This mechanism mainly consists of an adapter engine and an adapter instance control algorithm.Compared to static service adaptation,dynamic service adaptation only mediates partial interactions of services so that the adaptation overhead and failure risks are significantly reduced.As the dynamic service adaptation also has failure risks,this dissertation propose applying service adaptability analysis in dynamic service adaptation process.The method for dynamic service adaptability analysis determines service adaptability of a running state through a depth-first traversal of the state space of the subsequent interactions after the state.Combined with this method,we present two improved adapter instance control algorithms.One can return before failure occurs,which has values on error recovery of real-time systems;the other can avoid service adaptation failure by limiting executable interface actions of running services.(6)Methods for security service adaptationSecurity service adaptation is capable of decrypting and authenticatingmessages received by the adapter,and capable of encrypting and signing messages sent by the adapter.A preliminary study on security service adaptation is presented in this dissertation.We extend HESM with security attributes and functions,including key,time stamp,encryption,signature abstracted from WS-Security Foundation.On this basis,we present two methods for respectively generating and verifying security adapter specifications.The former firstly simplifies security extended HESM as HESM,and then generates the interface action mappings corresponding to the simplified HESM,thereby generating the security adapter specification.The latter verifies the generated security service specification,mainly including message parsing and message building processes,and finally returnsa set of data which will be used as the initial information of the adapter.We determine the correctness of the security service specification by analyzing each data attributes in the returned set.In addition,the security adapter specification can also assist security verification of service interactionsat runtime.To sum up,we present well-evaluated solutions in this dissertation for some key issues of service adaptation.Our contributions make a nice groundwork for future research and engineering on service adaptation both in theory and practice.