SPATIAL DATABASES

The entity-relationship model is a tool for analyzing the semantic features of an application that are independent of events. This approach includes a graphical notation, which depicts entity classes as rectangles, relationships as diamonds, and attributes as circles or ovals. For complex situation, a partial entity-relationship diagram may be used to present a summary of the entities and relationships that do not include the details of the attributes.

The entity-relationship diagram provides a convenient method for visualizing the interrelationships among entities in a given application. This tool has proven to be useful in making the transition from an information application description to a formal database schema.

The entity-relationship model is used for describing the conceptual schema of an enterprise without attention to the efficiency of the physical database design. The entity-relationship diagrams are then turned into a logical schema in which the database is actually implemented.

A conceptual model of a spatial entity that has geometry in a space is the following:

To model two spatial entities, one could explicitly define the spatial relations between them, such as that a river can traverse one or more lanparcels.

Another way to model two spatial entities is to have geometry as common third entity to which both entities are related by a relationship of located_at. In such case, spatial relations are derived during a manipulation of the data.

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