Entities, Attributes, and Relationships

An ER diagram uses about nine symbols. That is the whole language.

Learn what each shape means and you can read any Chen notation diagram, including the crowded one at the end of this chapter.

This lesson takes them in order: the shapes, then entities, then the five kinds of attribute, then relationships.

The symbols

Three of these are worth stating in words, because they are the ones people mix up.

A double ellipse means a multivalued attribute, not a derived one. A student with three phone numbers is drawn with a double ellipse.