by Peter C
According to the article, Supertype entities are similar but different from Subtype entities. Supertype and subtype entities have a relationship such as parent to children. They both share some common attribute within themselves. For a subtype entity, it has some unique attributes that are different from the other subgroups entities. Some of the attributes are also different from the supertype entity. For example, People can be your super entity and for your subtype, it can be vendors, employees, and customers. These primary key must be the same as the supertype entity. As for the subtype entities, it can contain some attribute that are not the same as each other.
I believe that by having these entities, it will let us see the company operation a little better. It shows who control what and where the data is coming from. It tells us all the information that we want to know such as name, address, city, etc. In our subgroup, it will give us the attribute that the person wants to see. It wouldn’t show them the other information from another subgroup or subtype entity.
In an Enhanced ER Model, supertype and subtype entities are used for creating this model. Supertype and Subtype entities are supposed to organize the database a little better. It will show us the relationship between these entities. It will also provide us with some helpful information that is in these entities. The entity will give us an idea of how the system is run which will create us a picture in our head. That is the purpose of creating the EER Model.
Supertype & Subtype. Retrieved Oct. 16, 2011, from learndatamodeling.com: http://www.learndatamodeling.com/dm_super_type.htm