Subtypes are subsets of a data set. They are generally used when we want to have data from a data type since, even if they are different in some aspects, they are still that type of data. They are also used when we want for equal concepts to be called differently.

Each subtype is formed by attributes, which are the same type of data as the attributes that correspond to their supertype. For this reason, the subtype attributes "inherit" the definition of the supertype.

In any group of attributes of subtypes that we define, there must be an attribute or set of attributes whose supertypes correspond to the primary key of a table.

To continue reading about how to generate subtypes correctly and to remember how they work, click here.