Next: SGML DTD for a
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:
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.
- Attributes and possible values of the attributes;
- Associations (or relationships) with other entities.
Figure 5.1: Entity-Relationship diagram for subcategorisation information