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.