Key Technology Of Distributed GIS Service Chain

With the development of Internet, Web is changing from static information publication platform to dynamic computation platform. The wide application of geospatial information in various domains is pushing GIS (Geographical Information System) developing from platform-dependent, tight-coupling, closing system to distributed, loose-coupling, open system. The emergence and development of Web Services technology provides a new distribute heterogeneous integration and interoperability platform. The combination of Web Services and GIS is becomming the main research focus. International organizations such as OGC (Open Geospatial consortium) and ISO/TC211 have done lots of fundamental research on GIS Web Service and have got universal consensus in geospatial information domain. Today, with the constantly enrichment of GIS Web Services, the most challenge we are facing now is how to dynamic combine those existing GIS Web Services to implement more complex tasks, thus to achieve the on-demand distributed geospatial information integration. This paper studies the key technology of distributed GIS Service Chain (DGSC). After analyzing existing distributed GIS integration methods, the paper proposes distributed GIS service chain integration method and integration architecture. Based on this integration architecture, key issues of GIS service chain integration are thoroughly studied.First, this paper studies the services foundation of GIS service chain—GIS data services and GIS process services that are the foundation of GIS service chain implementation. The main contents include following aspects:1) The GIS services implementation method based on Web Services technology is stutied.2) The performance optimizing strategy of Web Feature Service is put forward, including: strategy of CGML application schema definition, strategy of GML compression transfer and strategy of client side memory construction. Strategy of CGML application schema definition can lessen the size of GML by reducing the redundant property tags; strategy of GML compression transfer can make the decision whether to compress before GML transmission based on the size of GML document, bandwidth of network, performance of server and client. Strategy of client side memory construction can reduce frequency of remote request when users do some simple operation by memory structure of GML in the client side. The performance of the GIS data services can be impoved remarkably combined with these three strategies.3) Principle of GIS Web process interface definition is studied in order to satisfy the needs in GIS Web service chain integration. Following the principle, three common GISprocess services interface definition examples are proposed.Next, this paper studies the facility of GIS service chain—GIS services registration and finding mechanism. The mechanism of GIS services is the fundamental facility of GIS service chain integration. To make up capability lacks in GIS service classification of Current UDDI (Universal Description, Discovery & Integration), this paper extends UDDI through establishing distributed GIS service taxonomy. The main contents include following aspects:1) Aim at the needs of distributed GIS service chain, principle of distributed GIS Web services taxonomy is studied based on the analysis of current GIS service taxonomy. Following the principle, distributed GIS Web services taxonomy is put forward.2) A method of query GIS service is given using private UDDI which is extended by the distributed GIS service taxonomy.Finally, this paper studies the dynamic finding and combination of GIS service chain. Dynamic GIS service finding and combination are two difficult points in the research area of GIS service chain. To solve them, this paper proposes the service dynamic choice mechanism. Combining with semantic web and workflow technology, dynamic service finding and combination in GIS service chain based on semantic description of service and user specific requiremen is implemented using this mechanism. The main contents include following aspects:1) Dynamic service choice mechanism and the conception of Abstract and Concrete Services are put forward. Using dynamic service choice mechanism, Abstract services can be mapping into Concrete services dynamically, thus can save lots of time which users has to spend in finding service manually.2) GIS service semantic description method using OWL-S and WSDL is studied to solve the problem of lacking semantic description capability of Web Services technology and OGC service description mechanism. To deal with diverse user demands, this paper using ontology to describe user requirement during dynamic service finding.3) GIS service chain combination model and visual GIS service chain combination method are put forword. Users can compose GIS service chain in the visual environment by mouse drag operation.4) A method using workflow standard description language,BPEL4WS, to describe GIS service chain process is studied combining with workflow technology. And workflow engine is used to manage and monitor the executing of GIS service chain.In the sixth chapter, distributed GIS Service Chain prototype is implemented to prove the theories and methods proposed in the paper.and methods in the paper.This paper proposes a new distributed GIS integration method—distributed GIS service chainintegration. This method can satisfy the need of on-demand GIS services integration in the distributed heterogeneous Internet environment. Not only GIS data but also GIS process can be integrated through this method. The main contributions of this paper include:1. The performance optimizing strategy of GIS data services is put forward.2. The extended method of UDDI is proposed using distribute GIS service taxonomy.3. Dynamic service choice mechanism is put forward.4. Visual GIS service chain model is put forward.