3D Topology in Geo-DBMS

At present, no DBMS supports 3D topology.The problems with topology are much more complex compared to the geometry.Usually many application-related issues used to be taken into consideration, e.g. the space partitioning (full, embedding), the object components (volumes, faces), the construction rules (planarity, intersection constraints, etc.).The 3D topological data structures reported currently in the literature can be subdivided in two large groups: structures maintaining objects and those maintaining relationships.While in the first group (object oriented), most of the relationships between the objects are to be derived, in the second group (topology oriented), the representation of the objects has to be derived.Many structures, which are a typical example of explicit storage of objects, also maintain explicit storage of relationships, i.e.singularities.

Clearly, advantages of a topological representation in one of the aspects occur as disadvantages in another aspect.For example, the arbitrary number of nodes per face can be seen as an advantage and disadvantage for different applications.It is very convenient for modelling complex 3D objects (e.g.buildings) since an inappropriate partitioning (into triangles) is not required, but the operators for consistency check become very complex.

Since no agreement on a 3D topological representation exists, alternative approaches are investigated.Instead of looking for an appropriate 3D topological representation, it is suggested extending the DBMS kernel with meta information describing different topological structures in the DBMS.Such topological meta information can then be used both within the DBMS and outside the DBMS. In general, meta information (or system catalogs) of a DBMS contains descriptions of the data stored in the database: tables, attributes and types, and also contains descriptions of the available types and operators.