entities

Entities represents objects class (real or abstract), of the same flavor and that records will be stored as distinct values called Entity-type.

All the Entity-type must be described completly by their attributes, and at least one the entity attribute must act as an identifier to describe the occurs of the entity.

The identifier must be stable. It mustn't change during the Entity-type life.

relations

The relations exist to represent links between entity-types.

cardinalities

They indicate how many Entity-type belong to an association. For each association it is described by a minimal and a maximal Entity-type occurs.