What are supertype and subtypes in ER modeling?
A supertype is a generic entity type that has a relationship with one or more subtypes. A subtype is a sub-grouping of the entities in an entity type that is meaningful to the organization and that shares common attributes or relationships distinct from other subgroups.
What is Supertype subtype hierarchy?
A supertype entity in one relationship may be a subtype entity in another relationship. When a structure comprises a combination of supertype/subtype relationships, that structure is called a supertype/subtype hierarchy, or generalization hierarchy.
Does a subtype need a primary key?
Every dependent and category (subtype) entity in the model must have a foreign key for each relationship in which it participates. Foreign keys are formed in dependent and subtype entities by migrating the entire primary key from the parent or generic entity.
Can a subtype have a primary key?
The primary key of a subtype relation will also be a foreign key that references its supertype relation.
What is entity subtype?
An entity subtype is a more specific entity type that is related to an entity supertype, where the entity supertype contains the common characteristics and the entity subtypes contain the unique characteristics of each entity subtype.
What is the E-ERD supertype-subtype relationship?
One of the most essential things incorporated into the E-ERD is the supertype-subtype relationship. But first thing’s first, what are supertypes? Supertypes are a subgrouping of entities in an entity type with attributes distinct from those in other subgroupings.
What is the supertype of employee?
the “Employee” supertype of entity is introduced. This supertype contains common attributes for all types (subtypes) of entities; entity subtypes “Administration”, “Teacher”, “Support staff” are introduced. Each of the entity subtypes has its own unique attributes. Figure 1. Supertype and subtypes in the diagram 2. What is an entity supertype?
What is a supertype in Entity Framework?
This supertype contains common attributes for all types (subtypes) of entities; entity subtypes “Administration”, “Teacher”, “Support staff” are introduced. Each of the entity subtypes has its own unique attributes. Figure 1.
How can we apply the rules of supertypes and subtypes?
Apply the rules of supertypes and subtypes by evaluating the accuracy of ER diagrams that represent them You can typically associate ‘choices’ of something with supertypes and subtypes. For example, what will be the method of payment – cash, check or credit card? Understanding real world examples helps us understand how and when to model them.