Identifying Relationships between Entities

After subdividing the data by entities, the next step of design is to identify meaningful relationships between the entities described so far. For each relationship you identify, an attribute or group of attributes must support the relationship.

What are the relationships among the entities in the sample data? For the Album and Selection entities, there is a relationship of Content, that is, each album contains a specific group of selections. For the Composer and Selection entities, the relationship is one of Authorship; each composer has created one or more selections.

Another kind of relationship exists between Selection and Composer, namely, Period. The attributes that define Period are the composer's "Name" and "Birth Date."