UML is popular for its notations. We all know that UML is for visualizing, specifying, and documenting the components of software and non software systems. What’s more, UML has many types of diagrams which are divided into two categories. Some types represent structural information, others general types of behaviors. Among these, there is one that is commonly used for entity relationship diagrams.
In UML, an entity is represented by a rectangle:
Relationships are solid lines with cardinality specified at the ends of the lines:
Generalization is represented by an empty arrow:
Aggregation is shown as binary association with a hollow diamond as a symbol of the aggregation at the end of the association line. The part entity can belong to more than one aggregate classifier and it can exist independently of the aggregate.
Composition is presented as binary association with a black diamond as a symbol of the composition at the end of the association line. A composition specifies that the lifetime of the part entity is dependent on the lifetime of the whole entity.
Let’s model our book and chapter example using UML notation.