Research On Web Processing Service Based On Code Transmission

Geographic Information System (GIS) is single computer form, then gradually develops towards GIS based on internet. With the emergence and development of Web services, the GIS platform is headed for the direction of GIS based on Web service, Grid GIS and Cloud GIS, the inner power is the demand of data sharing and interoperation function. The Web service is the important way and development trend of spatial data sharing and interoperation in the future. OGC, ISO and other institutions developed a series of GIS services standards, these standards make different GIS system have an unified interface of data sharing and interoperation, to standardize the web service based method of the data access and sharing. The standard on WPS (Web Processing Service) published in2007is a specification oriented to function sharing, this standard will make the ablility of GIS about data sharing and interoperation be raised to a new height--function sharing, has the vital significance. Function sharing and interoperation based on WPS will lay a foundation for the implementation and development of Grid GIS and Cloud GIS, which make GIS can realize the real distribution, sharing and interoperation for spatial data, spatial analysis function module.The OGC WPS implementation specification has some obvious shortcomings, which limit its application and extension. Some outstanding problems are:(1) in invocation and execution process of OGC WPS services, there is a contradiction between the limited transfer speed of internet and the high data transmission quantity;(2) OGC WPS is dependent on the massive spatial data repeated transmission, which makes the construction of WPS service chain is difficult;(3) the OGC WPS specification requires repeated transmission of spatial data with GML format encapsulated in XML format, therefore, the safety of the spatial data safety could not be guaranteed.In this paper, aiming at the existing problems of OGC WPS model, for improving the efficiency of WPS calls and the safety of spatial data, by utilizing the existing network technology, a new WPS model and some technologies are studied to avoid or reduce the space data transmission amount. Firstly, through the use of code transmission instead of spatial data transmission, a new model of Code Transmission based Web Processing Service (CTWPS) is proposed; secondly, the paper put forward an implementation technology system of CTWPS model and do research on service combination based on CTWPS, which is compatible with OGC WPS standard and existing OGC Web services framework; finally, a prototype experiment system is developed, and the paper verified the related theory and technology of CTWPS. Specific content is as follows:(1) The paper summarizes and analyzes the relevant theory and technology of geographic information services, including OGC WPS1.0.0standard, OGC geographic information service chain standards and the deficiency of OGC WPS is analyzed and summarized,.(2)Based on the research and analysis on the existing Web service mode, code transmission concept, new concept and theoretical model of code transmission based Web services and code transmission based WPS (CTWPS) is put forward in the paper. Keeping compatible with the existing OGC WPS standard, based on the extension of OGC WPS standard, the CTWPS interfaces and data structures are defined.(3)In the paper, the CTWPS technology framework, based on4layers of code database, server, transmission and client, is put forward, and the technological design of each layer in this framework is accomplished.In this part, the program technology to realize CTWPS model is proposed, and some example are listed; to protect code safety and user security, a CTWPS security control mechanism based on2layers is designed; at the same time, CTWPS local agents model are put forward to ensure that CTWPS can use in exsiting clients of OGC WPS without modifying and changing.(4) Based on the analysis on WPS service chain model, GIS services combination model and technology, the paper put forward the theoretical models and technology of CTWPS service chain, then an example of CTWPS service chaining with KVP method is given out to verify the self-combination ability of CTWPS. Paper also does research on general models of CTWPS combination, and realize the combination ablility of CTWPS with other OGC GIS services.(5) Based on the theory and technology proposed in this paper, a CTWPS experimental system including multi-kinds clients is developed, which verified the theory and technology put forward in this paper; using the experimental system, some contrast experiments between OGC WPS and CTWPS are accomplished, and the experiment results proved that the CTWPS has obvious advantages in the aspects of calls efficiency, reliability and data transmission amount when it is compared to the OGC WPS.