Studies On The Key Techniques For Development And Application Of Geospatial Metadata In Water Resources

For information sharing, new requirements are proposed with the further development of informationization construction in water resources. In applications of water resources, geospatial information is the spatial carrier of various thematic information, and its amount reaches about 80% of information gross. Therefore, geospatial information sharing plays a very important role in the operation of information sharing in water resources industry.The key condition of information sharing is that information can be searched and located on condition with network techniques rapidly developed and information amount speedily increases. Geospatial metadata describes and explains the content, quality, condition, expressing style, spatial reference system, management mode and other characteristics of geospatial data, which can help and encourage people efficiently to locate, evaluate, compare, get and use corresponding spatial data. Geospatial metadata reduce network communication loads when users query spatial data, and shield the differences between different data formats, which gives effective support to the first step toward geospatial information sharing under the web environment.Geospatial metadata is either a kind of data, and it also needs the development strategy of standardization. Unorderly geospatial metadata will add new technique bulwarks to information sharing. So there has been a growing attention to geospatial metadata standard in the field of geospatial information, and geospatial metadata standards are developed one after another in different countries, regions and industries.In Chinese water resources industry, issues of standardization construction and application of geospatial metadata are put on the agenda during deepening the construction of geospatial information sharing. But the development of metadata standards still remains on technique and experience, and it doesn't get scientifically theoretical guidance. In the face of current status of multi-source geospatial metadata standards coexisting, how to develop standards that are compatible with these ones and embody water resources industry characteristics must be solved. At the same time, search styles of keywords, provided by additional geospatial catalogue techniques based on geospatial metadata, have obvious drawbacks in the face of various expressions made by regional autonomy management in water resources industry, and presently low recall and precision have direct effect on deep implementation of information sharing.Allowing for these problems above, this paper makes researches below to supply better solutions for development and application of geospatial metadata in water resources industry:This paper discusses conceptual differences between metadata and geospatial metadata, analyzes the necessity of geospatial metadata existence as a branch of metadata under the environment of rapid development of metadata application in the field of geospatial information, introduces presently superior geospatial metadata standards and content differences between them. After descanting functions of geospatial metadata, taking functional morphology of metadata and abundant connotations evolved by the morphology of human cognition as a guide, this paper makes researches on inherent relationship between metadata element, entity and section, proposes this concept morphology of geospatial metadata, and uniformly understands different logical division units of geospatial metadata from the view of relation. It analyzes drawbacks of current operating programs and methods of metadata standards in using them to develop geospatial metadata standards, combining with"Object"hypostases of geospatial metadata morphology, constructs object model of geospatial metadata, and based on these works, makes researches on the developing method of metadata standard of geospatial information combining with the Object-Oriented method and prototype method in software engineering. Then this paper proposes and designs the Object-Oriented prototype developing method of geospatial metadata standard which is implemented from 3 hierarchies of metadata classes, Object-Oriented software engineering and requirements of operating programs of national standards, which ensures that the geospatial metadata standard can be developed not only from the microcosmic hierarchy combining with"Object"hypostases of geospatial metadata, but also from the system engineering with mature theories and methods as a guide, and the system method of geospatial metadata standard development is formed from the microcosmic level to the macroscopic one with macroscopic requirements of operating programs of national standards obeyed.This paper analyzes features of geospatial information in water resources, and determines the position and application scope of"metadata standard of geospatial information in water resources"and principles of standard development. And then this paper builds the set of function objects of geospatial metadata in water resources with the prototype method of Object-Oriented geospatial metadata standard development as a guide. After comparing and analyzing multi-source standards, this paper selects the national standard,"geographic information-metadata", as the standard prototype, based on this work, designs and realizes the Object-Oriented standard, does the development work of"metadata standard of geospatial information in water resources", and proves that the prototype method of Object-Oriented geospatial metadata standard development is feasible and scientific.This paper introduces commonly used geospatial catalogue techniques of Clearinghouse and OGC such as catalogue service, and combing with the fact that geospatial metadata is rapidly developing in water resources industry, analyzes existing problems in recall, precision and metadata interoperation when catalogue techniques above are used and the feasibility in using ontology to solve problems above. On the basis of introducing correlative knowledge of ontology, this paper proposes this idea that the geospatial semantic catalogue service is constructed to overcome drawbacks of current catalogue techniques based on ontology and catalogue techniques, and makes researches on these key techniques of building geospatial semantic catalogue service for water resources: 1) This concept and reference model of geospatial semantic catalogue service are defined; 2) The basic principles of constructing geospatial semantic catalogue service are determined; 3) Organization strategies of ontology in semantic catalogue service are studied and determined; 4) The relationship between the Object-Oriented method and the ontology method, geospatial metadata and ontology is discussed, and on the basis of this work, this method of building metadata ontology based on"Object"is proposed; 5) Researches on expressing mechanisms of formalization of metadata ontology are made. At last, this paper constructs web ontology service which can manage and search ontology, builds the application frame of geospatial semantic catalogue service for water resources by extending and appending web ontology service on the basis of catalogue service of OGC, and verifies through experiment prototype system that the geospatial semantic catalogue service in this paper is valid and feasible.