What is an entity Supertype and why is it used?

The reason for using entity supertype is to reduce redundant relationships and also reduce the number of nulls. Example: The following example demonstrates the “supertype” entity, “subtype” entity, and “discriminator”. Explanation: “Emp_type” is a discriminator to select appropriate “subtype”.

Supertype is an entity type that has got relationship (parent to child relationship) with one or more subtypes and it contains attributes that are common to its subtypes. Subtypes are subgroups of the supertype entity and have unique attributes, but they will be different from each subtype.

Also, what is an entity cluster and what advantages are derived from its use? 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.

Similarly one may ask, what is a composite entity and when is it used?

A composite (or associative) entity is a bridge entity used in ERD to resolve M:N relationship between two or more entities. • The composite entity contains the keys from all the entities which are bridged by this entity as its primary keys. It does not have any primary key of its own.

What is a disjoint subtype give an example?

Disjoint subtypes: Contain a unique subset of the supertype entity set. Each entity instance of the supertype may only exist as one of the subtypes. Based on business rules like: Airline employees may only be a Pilot, Mechanic, or a FlightAttendant.

Can a subtype be a supertype?

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 an associative entity provide an example?

An associative entity is the table that associates two other tables in a many to many relationship. An associative relationship attribute is an attribute of the associative entity that exists because of the many to many relationship. Here’s an example. It’s an attribute of the association.

What is a specialization hierarchy?

In a specialization hierarchy, the grouping of unique attributes into a subtype entity. See specialization hierarchy. specialization hierarchy. A hierarchy based on the top-down process of identifying lower-level, more specific entity subtypes from a higher-level entity supertype.

What is Disjointness constraint?

A constraint about generalization hierarchies. A disjointness constraint means that the subtypes do not share any common entities. In other words, the intersection of the sets of entities in the subtypes is empty.

What do you mean by cardinality?

In the context of databases, cardinality refers to the uniqueness of data values contained in a column. High cardinality means that the column contains a large percentage of totally unique values. Low cardinality means that the column contains a lot of “repeats” in its data range.

What is ER diagram in DBMS?

ER Diagram is a visual representation of data that describes how data is related to each other. In ER Model, we disintegrate data into entities, attributes and setup relationships between entities, all this can be represented visually using the ER diagram.

What is a supertype in Java?

18. There is a notion of supertype and subtype in OOPS, In java this kind of relationship is implemented by inheritance i.e. using extends keyword: class A {} // super class class B extends A {} //sub class. Any member (fields, methods) declared in super class is to be called supertype.

What is a subtype discriminator?

A subtype discriminator is the attribute in the supertype entity that determines to which subtype the supertype occurrence is related.

What is a bridge entity?

A composite entity is also known as a “bridge” entity. This “bridge” is used to handle the many-to-many relationships that the traditional entity could not handle. This entity lies between the two entities that are of interest and this composite entity shares the primary keys from both the connecting tables.

What is the difference between a composite key and a composite attribute?

A composite key is a key that contains more than one attribute. A composite attribute is an attribute whose value can be subdivided into meaningful attributes. In ER diagram, a composite key is indicated when several attribute names are underlined to specify its participation in the PK.

What is a recursive relationship?

A relationship between two entities of similar entity type is called a recursive relationship. In other words, a relationship has always been between occurrences in two different entities. However, it is possible for the same entity to participate in the relationship. This is termed a recursive relationship.

How is a relationship between two entities indicated in a crow’s foot ERD?

An entity is represented by a rectangle containing the entity name. Instead, the Crow’s Foot ERD uses relationship types – strong or weak – to indicate the nature of the relationships between entities. For example, a strong relationship indicates the existence of a weak entity.

Why must some identifiers be composite rather than simple?

Composite identifier or attribute: If an attribute can be able to break down into smaller meaningful component, then the attribute is called as composite attribute. Need for the identifiers to be composite rather than simple:*A simple attribute is not unique for all occurrences of an entity type.

What is a derived attribute give an example?

The derived attribute need not be physically stored within the database; instead, it can be derived by using an algorithm. For example, an employee’s age, EMP_AGE, may be found by computing the integer value of the difference between the current date and the birth date of the employee.