If a relationship has been established between two entities in the model (on any Subject Area diagram or the Model diagram), then when you draw those same two entities on another diagram (either a Subject Area or Model diagram) in the Model, the relationship between them will automatically be added to the diagram. This is called Representational Consistency in System Architect parlance -- the information of the relationship between the two entities is held in the repository; the diagram is just a reflection of this information.

By default in System Architect, the graphical notation of strong, weak, and associative Entity Types on a Subject Area reflects the local relationships on the diagram. This is by design, and is provided for a number of reasons, including performance in a multi-user environment and also that some users wish that a Subject Area reflect an isolated view of the model. To change this so that entity notations always reflect information in the model, enable Data Modeling Graphical Consistency for the encyclopedia.

The example below shows a Model diagram in which the entity Room is a Weak entity (reflected by its double-line border) because of its relationship to another entity in the model; in this case the entity Receptionist, which has an identifying relationship to it.

If you create a Subject Area diagram and place Room on it, Room's graphical notation will reflect the local relationships on the Subject Area diagram. In the example below, you can see that Room no longer has a double border around it, because on this Subject Area diagram, it is a Independent (Strong) entity in its relationship to the entity Bed.

If you turn on Data Modeling Graphical Consistency, the entity Room show sas a Weak entity (double line border) even though it seems to be an Independent (Strong) entity in the diagram. It is reflecting overall model information, that is, its relationships to other entities depicted on other diagrams in the model.