What are supertypes and subtypes?

What are supertypes and subtypes?

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.

How many Supertypes can a subtype have?

one supertype
In general, a supertype will have two or more subtypes. (Either that, or it will be possible for the supertype to have “instances of its own,” which aren’t also instances of the subtype.) However, a subtype is (directly) a subtype of only one supertype.

What is an example of subtype?

A simple practical example of subtypes is shown in the diagram, right. The type “bird” has three subtypes “duck”, “cuckoo” and “ostrich”. Conceptually, each of these is a variety of the basic type “bird” that inherits many “bird” characteristics but has some specific differences.

What are entity subtypes?

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.

Can subtypes have primary keys?

Subtypes are subgroups of the supertype entity and have unique attributes, but they will be different from each subtype. Supertypes and Subtypes are parent and child entities respectively and the primary keys of supertype and subtype are always identical.

Do subtypes 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. If the primary key is composite, it may not be split.

What is another word for subtypes?

In this page you can discover 11 synonyms, antonyms, idiomatic expressions, and related words for subtype, like: , haplotypes, allele, , isotypes, genotype, , subpopulation, isoforms, epitopes and serologically.

Why are entity Supertypes used?

An entity supertype is a generic entity type that is related to one or more entity subtypes, where the entity supertype contains the common characteristics and the entity subtypes contain the unique characteristics of each entity subtype. The reason for using supertypes is to minimize the number of nulls.

What is the purpose of entity cluster?

An entity cluster is considered “virtual” or “abstract” in the sense that it is not actually an entity in the final ERD. Instead, it is a temporary entity used to represent multiple entities and relationships, with the purpose of simplifying the ERD and thus enhancing its readability.

Which is the best definition of a supertype?

· A means of classifying an entity that has subtypes. – Supertype. · Something an entity may be split into based on common attributes and/or relationships. – Subtype. · Each instance of a supertype is an instance of only one possible subtype.

How are supertypes and subtypes mutually exclusive?

Mutually Exclusive: Each instance of a supertype is an instance of only one possible subtype. At the conceptual modeling stage, it is good practice to include an OTHER subtype to make sure that your subtypes are exhaustive — that you are handling every instance of the supertype.

How to identify supertypes and subtypes in ERD?

Read the following scenario and construct an ERD that contains at least two subtypes of the entity PRODUCT. Show clearly which attributes belong to the entity supertype, and which belong to the subtypes. Identify a UID for the entity.

Which is the supertype for the entity here employee?

Here employee will be the superset for the entities HR Employee and IT employee, but again it is a subtype for the PEOPLE entity. A person can open a savings account or a certificate deposit (fixed deposit) in a bank.