Database Systems with SQL - Full Course - Database Systems - IsA Relationship - Supertype and Subtype Entities

A subtype entity is a subset of another set of entity instances called the supertype entity. For example, Cars are a subset of Vehicles, so Car is a subtype entity of the Vehicle supertype entity. When creating an ER diagram, place the subtype entities within the box for the supertype. It’s also possible for several subtypes to belong to one supertype. All the attributes of each subtype also are attributes of the subtypes, but not to other subtypes within the supertype. An IsA relationship is when a subtype entities depend on the supertype. For example, a Car-IsA-Vehicle. A GasGrill-IsA-BbqGrill. You can represent IsA relationships in an ER diagram by drawing an arrow from the subtype to the supertype. Or just place the subtype box inside the supertype box. Similar entities are entities that share common attributes and relationships. Both supertype and subtype entities are considered similar entities. A supertype entities partition is a group of mutually exclusive subtype entities, which do not share common instances. For example, Musician and Painter are mutually exclusive subsets of Artist. Each of the partitions corresponds to a partition attribute of the supertype entity. The partition attribute indicates which subtype entity each instance belongs to. For example, salary is a partition attribute of the Artist supertype entity. Code ‘M' indicates the artist is a musician, and code ‘P' indicates the student is a painter. A supertype entity can have many, one, or 0 partitions. In the diagram on the bottom, the sportscard has two partitions. Hockey, Basketball, Baseball, and Football partition SportsCard. SportType is the partition attribute. Another partition are the card brands Topps, Fleer and UpperDeck. The partition attribute is Brand. When designing a database, creating supertype and subtype entities are done at the end of the analysis steps: - Discover all the entities, relationships, and attributes - Determine the cardinality - Determine the independent and dependent entities - Create all supertype and subtype entities Subscribe to Appficial for more programming videos coming soon. Also, don't forget to click LIKE and comment on the video if it helped you out!