The Balance Between Geometry and Topology

The architecture of Geographic Information Systems (GISs) is changing: more and more systems are based on the integrated architecture, i.e. storing geometric data in the Data Base Management System (DBMS) together with administrative data. The first step is having data types and operators for the simple features (i.e. geometric primitives): point, line and polygon. This has reached the level of standardization and is now implemented in several commercial DBMSs. The next step is also having support for the topologically structured features in the DBMS, i.e. complex features. The DBMS can check and guarantee consistency. Also complex operations can be executed within the DBMS. Despite the fact that topologically structured models are well known and that it is not difficult to store the topological references, it still remains an open issue how to implement these models completely within a relational DBMS. In this paper we describe a design and implementation of topologically structured management at the DBMS level. Our main focus is to translate topological structures into geometric primitives. It is then possible to define a DBMS view on a topological primitive, which makes this to appear as a geometric primitive. This allows best of both worlds: on one side the advantages of topological structure (no redundancy) and on the other side the ease of explicit geometric primitives in querying, analysis and presentation.