Spatial Data Organization and Management in GeoStar

GeoStar is an object-oriented geographical information system,which integrated various data sources such as vector,attribute,DEM and image.In this paper,the authors discuss Geo-Star's vector object model,data organization,data management and object implementation. In GeoStar,spatial objects are classified into point object,line object and surface object,etc.according to their geometrical features.The attribute data of these objects are stored in relative tables and are connected by an object identification (OID).GeoStar organizes these objects into feature classes and workspaces and then a project.In order to manage the objects,features,workspaces and projects,an object storage manager and object manager are developed.The object storage manager is mainly in charge of accessing of various spatial objects,establishing spatial index, accomplishing storing permanent objects and making spatial operation log and resuming the spatial objects when it is necessary.The object manager is mainly in charge of creating spatial objects,assigning the unique ID of object and workspace,completing every fundamental spatial query,maintaining the consistency of spatial objects,accomplishing multi-users management and management of feature classes,feature layers,workspaces and projects under the network circumstance.A set of classes which manage the objects,features,workspaces and projects are also provided,and can be used to develop applications by user. GeoStar organizes spatial data on the basis of object-oriented method.According to the idea,everything and conception in real world are described as objects.A spatial linear object or a surface object may consist of thousands of points.Two methods can be used to realize the spatial object.One is describing inner points of a line or an area as independent point objects,making it easy to do a variety of operations with every point object; the other is not describing inner points of a line and a surface as a whole instead of single point object.Consequently,the inner information must be interpreted by the methods.If we characterize every point as an object,instantiating an object of a line or a surface need too much of "new" operation."New" operation itself spends too much time,and also brings memory fragments.Both of them lower the efficiency of system.Therefore,the second method was adopted in the implement of line and area objects in GeoStar. The experience of the implement of GeoStar indicates that organizing and managing spatial data with object-oriented method is feasible.But,in the implement of object-oriented method,we should not use the pure conception of object-oriented,or else it will lower the efficiency of system.