The diagram depicts the data model of the Travel Agency application.
This particular diagram shows:
•Primary keys - indicated by a key icon .
•Other mandatory columns - indicated by a red rectangle.
•Non-mandatory columns - indicated by a green rectangle.
•Role names, e.g. GUIDES, FOR WHICH ARE MADE.
•Cardinality, e.g. 1-to-1 relationship or 1-to-many relationship.
•Supertypes and subtypes.
Among other things, the diagram does NOT show or identify.
•Which columns are foreign key in a relationship.
•Co-role names, e.g. IS GUIDED BY, MADE FOR.
•Domains, domain characteristics.