Because subject areas and entity types are shown on the same diagram, the use of color or shading is essential.
It is useful to distinguish major entity types from other entity types and also from subject areas. Use either different coloring, shading or a highlighted box.
Relationship types are the same as in a nonsummarized entity relationship model. Although there are some restrictions, there is also increased flexibility.
Relationship types can be shown from a major entity type to a complete subject area:
Cardinality and optionality are derived from an aggregation of all the relationship types from the major entity type to the subject area.
On the detailed diagram corresponding to the related subject area, the relationship type is shown to the appropriate nonsubject entity type:
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