DATA MODELLING

 Data modelling is performed via Datatype(DD) and Entity Relationship(ER) diagrams.
The diagram may contain the following elements :
Entity Besides it's name and informal description, an entity can contain a number of formal attributes :
  • datatype - a record datatype name
  • primary key - a list of fields forming the primary key of the entity
Relationship It can contain a number of formal attributes :
  • role name - one for each of the relationship ends
  • cardinality - zero or one, just one, zero or many, one or many
  • foreign_key - a list of fields forming the foreign key for this relationship

Nested (subtype and part-of) entities are also available.