The Research Of Metadata In Spatial Data Warehouse

Due to the limitation of science and technology, previous geographic spatial products, such as maps and image, are almost made, published and printed in traditional ways, whose abundant contents are also used, filed and preserved in paper. With the various needs of geographic spatial products in every domain, the confinements of using these pictures supplied in paper are becoming more and more obvious. With the rapid development of computer and information technology, geographic spatial database can be built by digitalizing many maps or images. It is very significant and practical for making full use of spatial products' rich contents and managing them uniformly over nation.To make full use of these collected data and share them, a special kind of data, no spatial data or attribute data-metadata must be depended on, which is used for describing the characteristics-content, quality and condition, etc-of geographic spatial data set. Metadata play an important part in managing, updating and sharing geographic spatial database system. Both the producers of data and the users realize the great value of metadata. So, with the increasing population of data producers and users, it is the inevitable trend that using proper metadata documents to produce, store, update and reuse data. The ex-vice president of American also considered metadata as an important technique to support digital earth in his talk about "digital earth". To make users draw out needed geographic spatial information from huge database correctly and efficiently, we must organize and manage data scientifically. With the rapid development of internet and web, with the rapid increasing demand of managing, sharing and telneting information, the technique of metadata gradually becomes the core and basis of sharing information and mutual operation. It will also become one of the core techniques of distributed information computing. So it's paid widespread attention at present.To form the sharing mode of unified operation at geographic spatial data and make the standard, collected drawing out of geographic spatial data come true, spatial data warehouse system must be developed, which is much more complicated. However, no matter how complicated the system is, to realize spatial data warehouse, we must resolve problems of two levels. Firstly, many geographic spatial database should supply sources of data for spatial data warehouse. Secondly, spatial data warehouse should supply standard, collected geographic spatial data and service for kinds of applied systems. Therefore, spatial data warehouse is between geographic spatial database and appliedsystem, which has built a bridge for providers and users of geographic spatial data. To construct this bridge, geographic spatial metadata must be needed.Geographic spatial metadata play a significant role in the course of building spatial data warehouse. First of all, it indicates how spatial data warehouse draw out various geographic spatial data, such as data category, data standardization, maths foundation, data format etc from many geographic spatial database. Secondly, it indicates how applied systems draw out standard, collected geographic spatial data from spatial data warehouse and provide service of geographic spatial, digital products for users. Previous geographic spatial metadata were only designed for a certain geographic spatial database or spatial data set, whose content and scope have been unable to satisfy the need of spatial data warehouse. So, metadata research based on spatial data warehouse has become very popular nowadays in the domain of geographic spatial metadata in the world. It's also one of the chief problems that should be solved urgently with regard to spatial data warehouse. Whether the research succeeds or not directly influences the result of spatial data warehouse's research. So, metadata research based on spatial data warehouse is of great value and very urgent.Based on studying and summing up great many internal and international research achievements about geographic spatial me...