An Entity Relation or IDEF1X Subject Area diagram represents a portion of a model or system. Subject area diagrams can share entities and relation lines, or the user can define an entity for use within only a single subject area diagram.
•When entity pairs appear in more than one subject area in the same project model, the relation lines between the two entities are always identical.
•All entities added to a subject area diagram are automatically added to the model diagram when the model diagram is refreshed. However, an entity must be explicitly added to a subject area diagram.
The Subject Area diagram is refreshed automatically each time the diagram is opened, or you can refresh it by selecting Dictionary > Refresh. When a subject area diagram is refreshed:
•All relationships shared by entity pairs that are on other diagrams in the model are added or updated.
•All entities and relations that have been removed from the model are removed from the subject area diagram.