A Study On Geographic Information Services Combination And Spatial Analysis Service

Internet is an important intermedium of information issue and transmission. It has been developing with a high speed. Nowadays, it has been becoming a media of Web Services. Web-oriented services develop quickly and services fields become more widely. The adventure and development of Web Services technologies and specification bring another information technology storm. The development of software industry has experienced integration, modularization, object orientation, and component. Now it is developing towards Web Services.With the adventure of XML and Web Services, Web application developing mode has been changing. XML is greatly capable of self-description. It separates data content and data presentation. It has been proved that XML is very suitable of implementing Web information share and heterogeneous application data exchange. Web Services refers to a set of XML specification and technologies which partly implement service-oriented architecture (SOA).SOA is a special kind of software architecture that has several unique characteristics. Different from technologies-oriented architecture, SOA deals with services. The most important aspect of SOA is that it separates the service's implementation from its interface. The unique characteristics of SOA includes as the following. Services are discoverable and dynamically bound; Services are self-contained and modular; Services stress interoperability; Services are loosely coupled; Services have a network-addressable interface; Services have coarse-grained interfaces; Services are location-transparent; Services are composable; and Service-oriented architecture supports self-healing. SOA support the "find, bind, and execute" paradigm. SOA consists of six entities of service consumer, service provider, service registry, service contract, service proxy and service lease configured together to support the find, bind, and execute paradigm.Compared with technologies-oriented application, services treat technologies from the point of business processes, which is opposite from technologies-driven business processes. SOA can resolve the problem about services description and interoperation, which make it possible to combine services with business processes tightly together. Therefore, business processes can be accomplished with services combination.Geographic Information System (GIS) is always influenced by the development of information technologies. Nowadays, it is unavoidable to develop towards Web Geographic Information Services (GIServices). OGC has proposed OpenGIS WebServices Architecture and interoperate protocol stack which have been supported by many GIS providers. More and more provider has been packaging their products into Web Services, which change the situation of developing WebGIS with private technologies. More and more will be put on the Web. Single Web GIService provides particular function. How to combine Web GIServices to accomplish Geographic Information tasks that can not be accomplished by on service is worth studying. This paper is focused on GIServices combination, which is significative.According to the development status of inland and abroad, study on GIServices combination is still at primary stage. Study of GIServices Combination involves many fields some of which is explored in this paper. This paper focuses on GIServices Combination concepts and models, GIServices taxonomy system and its influence on GIServices Combination.Firstly, the concepts and abstract model of GIServices Combination are studied in this paper. According to the service combination concepts of SOA, ISO and OGC, services combination are classified as discrete combination and chain combination. It is proposed that service combination can be recursive, which means that composite services can also be combined. It is called hybrid combination. In consideration of service final consumers - users, it is believed that chain combination is the main services combination form. This paper focuses on the study of chain service combination based on workflow theory. Service combination (chain form) is related with workflow. Concepts of service item and service instance are brought forward according to work item and activity concepts in workflow. Service combination three-dimension perspective is produced according to that of workflow. On the other hand, there exist differences between service and task, service instance and activity, service combination and workflow. It is proposed that service combination should be built based on users tasks, which is called as tasks/activities-oriented service combination.Petri Net is very suitable for workflow model. Rachid Hamadi and Boualem Benatallah have proposed to model web service control flow and web services combination with Petri Net. The model they built is extended and a high-level service combination model based on Petri Net is produced in this paper. Service combination is directly mapped into a Petri Net. Services are modeled by transitions and the state of service combination is modeled by places. The arrows between places and transitions are used to specify causal relation. Internal activities of service are hided and a service is modeled as a single node in the net, which makes the combination relationship clear and the control of combination behavior easy. Based on the high-level service combination model, five chain forms, sequence, unordered sequence, alternative, parallel without communication and iteration, are depictedwith Petri Nets.Secondly, GIServices taxonomy and its influence on GIServices Combination are studied with emphatically. To implement tasks/activities-oriented geographic information services combination, correspondence between users tasks and service types and matching between activities and service instance which is concerned with geographic information process semantics should be established. Semantics of geographic information service is concerned with services taxonomy.Two existing GIServices taxonomy are discussed. One is proposed by ISO/OGC based on Extended Open Systems Environment. The other is based on tasks taxonomy. The disadvantage of the former is that it is not suitable to built services combination by users. The disadvantage of the latter is that service semantic granularity is simplex. To overcome these shortcomings, a multi-level services taxonomy system based on users and tasks is proposed. Geographic information tasks are classified at different users level including common market users, high-level expert users and low-level expert users. Consequently, the GIServices taxonomy consists of high-level taxonomy and low-level taxonomy.GIServices taxonomy has influences on service metadata that is the basis of corresponding tasks with services type and accomplishing service instance matching. Service metadata is studied in this paper. Service metadata of service in users and tasks oriented GIServices taxonomy is created based on the services taxonomy and Service Information Model (SIM) of OGC Web Services (OWS).Different GIServices combinations based on different services taxonomy are analyzed and compared with use cases. It can be concluded that users and tasks oriented GIServices taxonomy system is more suitable for tasks/activities-oriented service combination. It can satisfy the task process requirements of different users.On the basis of GIServices model and taxonomy, Spatial Analysis Service is investigated in this paper as the second theme. Many processes can be done on geographic information. Among them spatial Analysis is one kind of geographic information process and always used by users. In users and tasks oriented GIServices taxonomy system, spatial analysis service is one basic service of high-level and service corresponding with specific spatial analysis process is the basic services of low-level. Since existing services taxonomy is not based on users level and tasks classification, study on spatial analysis service is insufficient, which makes it valuable to study spatial analysis service in this paper. The study involves Spatial Analysis Service description (service metadata), service interface and its access mode, sevice access protocol and service implementation.In this paper, spatial analysis service is studied and implemented based on XML and Web Services. Firstly, Spatial analysis service metadata and service interface aredefined with XML. Access schema to service interface is given. To define request and response protocol which is used to access spatial analysis service, two geographic feature data schemas are defined firstly. One is called direct coordinate feature, the other is called indirect coordinate feature. According to feature data types of request and response, the interaction between service consumer and service is sorted as direct-direct, direct-indirect, indirect-direct and indirect-indirect interaction. They are all modeled with Petri Nets. The request/response message schemas are then defined with XML.Then, a physical architecture of implementing spatial analysis service based on Java Web Services, J2EE is proposed. Then spatial analysis service implemented is combined with feature provide service and feature render service for a specific use case.Finally, the performance of spatial analysis service implemented with XML and Web services is evaluated through comparing it with another service which is accessed with bytes stream protocol. In the comparing experimentation, same features are selected to conduct same spatial analysis operation with two different services. The result shows that the volume of data in XML schema is obviously greater than that in bytes stream format and the time consumed to access spatial analysis web service is obviously longer than that of comparing service. Therefore, the performance of service implemented with XML and Web Services should be improved. It is suggested that the data volume can be reduced greatly with indirect coordinate schema, which can improve the service performance.Summarily, two themes are involved in this paper. Some primary research work about GIServices combination is conducted, and spatial analysis service is studied and implemented in this paper. Study on the latter is based on that on the former. Main contributions and innovations include the following. CD Problems of GIServices combination are studied. A Petri Net-based high-level services combination model is proposed. (2) Users and Tasks Oriented GIServices taxonomy is brought forward. Service metadata is built based on this taxonomy. (3) Spatial analysis service interface, interface access schema and sevice access request/response message schema are defined. (4) Spatial analysis service physical architecture experiment is conducted based on Web services and J2EE. A spatial analysis service instance and its combination with other GIService instance are implemented.All the work in this paper represents an attempt to the research and application of GIServices combination, which can be useful for later research.