What is supertype and subtype entities?
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 a subtype entity?
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 an entity supertype and subtype and why is it 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 an entity Supertype and when it is used?
1. What is an entity supertype, and why is it 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.
Can a subtype have a primary key?
The subtypes will have the same primary key as their supertype.
What are the advantages of clustering entities?
It is a virtual entity which gives benefit to present the multiple entities and relationship in the ERD. An Entity cluster is used to combine the multiple entities and relationship which relate each other into a single entity. It is also used to simplify the ERD and increasing its readability features.
Why do we use entity supertype?
The idea of using an entity subtype is that a supertype is allocated for the entire diverse set of entities, which contains information common to all types of entities. Details (subtleties) of each type of entity are taken out separately in several specialized subtypes. Example.
Which is a weak entity?
In a relational database, a weak entity is an entity that cannot be uniquely identified by its attributes alone; therefore, it must use a foreign key in conjunction with its attributes to create a primary key.
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.
What is a strong entity?
Definition of Strong Entity The Strong Entity is the one whose existence does not depend on the existence of any other entity in a schema. It is denoted by a single rectangle. A strong entity always has the primary key in the set of attributes that describes the strong entity.
What is considered a entity?
A person or organization possessing separate and distinct legal rights, such as an individual, partnership, or corporation. An entity can, among other things, own property, engage in business, enter into contracts, pay taxes, sue and be sued.
How are entity subtypes related to supertypes?
An entity supertype is an entity type in which only common attributes are implemented (described) for entity subtypes that use this supertype. 3. How can entity subtypes be related together? Example Entity subtypes may or may not intersect.
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.
How does a subtype inherit from a supertype?
Enables an entity subtype to inherit attributes and relationships of the supertype All entity subtypes inherit their primary key attribute from their supertype At the implementation level, supertype and its subtype(s) maintain a 1:1 relationship Entity subtypes inherit all relationships in which supertype entity participates
How are nonoverlapping subtypes implemented in entity set?
Known as nonoverlapping subtypes Implementation is based on the value of the subtype discriminator attribute in the supertype Overlapping subtypes: Contain nonunique subsets of the supertype entity set Implementation requires the use of one discriminator attribute for each subtype