Research On Geo Web Services Based On Ontology

Web Services as a promising research field brings new opportunities and challenges to distributed GIS. However, industry standards of Web Services and OGC specification make Web Services incompetent to fulfill various requirements of the coming GIS applications under dynamic environment. The main inhibitor is the lack of semantics in the description of Web Services and discovery process. Therefore, new model of Geo Web Services is an active area of research in GIS.As a recently developed paradigm in semantic web, Ontology can especially benefit Geo Web Services applications on providing the semantics of services and requestor's requirement. Ontology is an explicit specification of a sharing conceptualization, which can be used in an integration task to describe the semantics of information sources and to make the contents explicit, also can be used for the identification and association of semantically corresponding information concepts. Considering the advantages of Ontology and Web Services technology, we propose a new paradigm in constructing Geo Web Services with the combination of both technologies, and further explore the related issues of its principles and techniques.This thesis presents the Geo Web Services model based on Ontology and architecture based on model, and addresses the fundamental principles and implementing techniques of Ontology in the model, describes a prototype. Major contributions of the thesis include: 1. A new paradigm of Geo Web Services based on Ontology is proposed based on analyse of industry standards of Web Services and OGC specifications. The introduction of Ontology to Geo Web Services brings new merits to make it more adaptable to open and dynamic Internet environment. The Geo Web Services model based on Ontology includes five layers: Network layer, Geo Web Services Publication Layer, Geo Web Services Discovery Layer, Geo Web Services Composition Layer and Application Layer. The Network Layer forms the lowest layer in the architecture and encapsulates standard network protocol (such as HTTP, SMTP and HOP) and SOAP allowing for exchange of object descriptions by standard means. In addition, machine agents need the possibility to communicate at an adequate level using protocols such as Knowledge Query and Manipulation Language (KQML) or Agent Communication Language (ACL).The Geo Web Services providers create Geo Web Services and their services definition that are based on Ontology, and then publish the services with the Geo Web Services registry based on OWL-S (an Ontology of service). Once a Geo Web Service is published, a service requestor may find the services via the registry. Geo WebServices Discovery Layer is used to find the appropriate Geo Web Services for the requestor's task. Geo Web Services are advertised using Ontology, which is used in service matchmaking too. Geo Web Services composition can be interpreted as pipelining services in a dependent series to attain a customized, more complex request. And this layer is responsible for carrying out the process of managing the discovery and integration of services to construct a composite service. The application layer embodies any application and human user that request the Geo Web Services. The application layer encompasses different GUI facilities to display the result of Geo Web Services and provides the functionality to initiate a request for Geo Web Services.2. Description architecture of Geo Web Services is proposed, which contains two levels: application level and conceptual level. Application level is Geo Web Services description based on OWL-S, which is given by Geo Web Service provider. The elements used in OWL-S are annotated with concepts from Conceptual level. The Conceptual Level is the level of human concepts and provides an agree-upon conceptualization by GIS Domain Ontology. The domain ontology makes a world view explicit and presents it in a machine interpretable way. Such domain ontology will never be complete since the meteorological knowledge evolves and the terms used change. But it will serve to describe a particular worldview on this domain and the vocabulary humans use to communicate about it. And domain expert should participate in the building of domain Ontology. This description architecture provides the Geo Web Services description of functional, non-functional and behavioral information in a semantic as well as in a syntactic form of representation. It also supports inferences on descriptions. This means that automated reasoning and comparison on descriptions will be possible and efficient.3. Geo Web Services discovery based on Ontology is proposed. The matchmaker is implemented based on matchmaking algorithm. The service provider advertises services to Registry. When matchmaker receives the requirement description of requestor, the services advertisements in Registry will be sent to matchmaker for capability matching. The result of the matching is the list of advertisements that are satisfied with requirements. Ontologies database contains ontologies of general knowledge, domain ontologies and knowledge concept ontologies, which are used to judge relation of elements of two descriptions. Matchmaker adopts techniques of information retrieve, AI and software engineering to calculate similarity degree between Geo Web Services description and requirements. This method can solute semantic conflict in traditional discovery and improve efficiency of discovery.4. A new dynamic service composition based on Ontology is proposed. Each workflow thatstored in the workflow repository is composed of one or more web services, which can be situated anywhere on the web. The OWL-S descriptions of the Geo Web Services are queried from the Registry, and the service matching that described above is applied. The workflow composer agent composes the executable workflow that comes from workflow repository based on composite process, and sends it into the workflow execution engine. Finally, the execution engine executes the workflow using the Geo Web Service instances.5. A simplified prototype of Geo Web Services based on Ontology is developed. Currently the system is implemented by using Protege3000 as platform for Ontology. User can describe, discover and compose Geo web services through this system. The success of the prototype shows that it is feasible to establish distributed GIS with Geo Web Services based on Ontology.