Next: Related Work Up: No Title Previous: Theoretical Foundation
The informal definition of Entity-Relationship (ER) diagrams is directly taken from  in order to demonstrate the expressiveness of our specification language and the reasoning capabilities of our DL system. Figure 2 shows an example ER diagram specifying a relationship between a pilot and an aircraft. We assume a few primitive concepts (denoted in slanted font) and spatial relations (touching, containing, linked_with, text_value) representing geometrical objects (rectangle, circle, diamond, line, text) and their relationships.
Figure 2: A simple entity-relationship diagram
A relationship-entity connection is a line that touches exactly one text label (expressing cardinality) and two other regions (rectangle or diamond). A cardinality is a text string with values chosen from the set .
An attribute-entity connection is a line that touches only two regions (circle or rectangle) and no text string.
An entity is a rectangle that contains its name. It touches at least one relationship-entity and optionally some attribute-entity connectors. It is linked with at least one diamond.
A relationship is a diamond that contains its name. It touches one relationship-entity and optionally some attribute-entity connectors. It is linked with two entities.
An attribute is a circle that contains its name. It touches one attribute-entity connector and is linked with an entity.