Conceptual representation of the specifications via E-R diagrams

The results of our work can be synthesised in an Entity-Relationship diagram (see figure 5.1) which is to be understood as follows. There are some conceptual elements, called entities, that are described by means of their:

Attributes and possible values of the attributes;
Associations (or relationships) with other entities.

Relationships link two entities and may carry attributes. Relationships importantly carry cardinality information that specifies whether an entity is necessarily or not involved in a relationship and whether it can be related to more than one entity with the same relationhip. Entities are here represented by boxes, relationships by a circle. In figure 5.1, just one relationship has attributes: the relationship between frame and slot. Cardinalities are expressed by pairs of numbers at each end of a relationship: each pair of numbers expresses the minimum and maximum number of relationships concerning all instances of the entity at that end of the relationship. So, when the minimum is 0, the relationship information is optional, and when it is 1 or more, it is obligatory. The cardinality indication 0,n means that zero, 1, or several relationships of the same type can relate with an instance of the entity (i.e. optionality is specified); 1,n means that 1 or several relationships can relate with an instance of the entity; 0,1 means zero or 1; 1,1 means exactly 1, and so on. For instance, a FRAME_SET entity can be related with 0, 1, or several RELATED entities and a RELATED entity is related with at least 1 but possibly many FRAME_SET entities.

Figure 5.1: Entity-Relationship diagram for subcategorisation information