The Technical Research Of Methods To Direct Access To ArcSDE Spatial Data Model

The two ways of spatial data storage are file-based and database-based. In file-based storage style the spatial data are stored in the file system. It has the advantage of esay-operating and low cost. But It also has seral problems: no-versioning, small capacity, lack of mechanism for concurrent multi-user access and poor safety. On the contrary these problems have been solved better in the database. The database provides record-level lock mechanism and supports cocurrent access by muli-users. Furthermore, data Integrity can be checked in the database so that data is always in the correct state. Database systems have improved access control, data security is guaranteed. Because of these advantage, the database-based management of spatial data has became the main trend of spatial data storage and been as a core part in distributed GIS system.ArcSDE is a famous commercial spatial database engine, which stores spatial data in the background database and manages it. In this paper the ArcSDE is compared with other spatial database engine. The ArcSDE conceptual data model is discussed and on this basis the storage schema of ArcSDE spatial data model is deeply researched. Through ODBC database access technology we implement the methods of direct access to ArcSDE spatial data. The content of research works is as follows:(1) ArcSDE conceptual spatial data model. Conceptual data model is the first level of description and abstract from the real world to the computer world. In this part the conceptual model and its responsing object are discussed.(2) ArcSDE vector data storage schema. Storage schema defines the struct and organization of data. In this part the table structure of vector data storage schema and principle of coding generation of binary flow are discussed.(3) ArcSDE raster data storage schema. In this part the organization of raster storage in the database are discussed, containing the principle of tiles, compressed coding.(4) The implementation of technical methods of access to ArcSDE spatial database. On the basis of ArcSDE data model and storage schema discussed above, we implement direct access to vector and raster data in the SQL Server 2000 through ODBC database access interface and analyze the underlying the storage schema.