Difference between strong and weak relationship database

What is the difference between Strong and weak entity? | Practice | GeeksforGeeks

difference between strong and weak relationship database

Difference between Strong Entity and Weak Entity - Weak EntityA weak DatabaseMCA In the given ER diagram, Dependent is the weak entity and it depends on the strong entity Employee via the relationship Depends on. The relationship between weak entity and strong entity set is called as Identifying The E-R diagram for the employee-dependent database is shown. There are. 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.

How to identify a strong vs weak relationship on ERD? - Stack Overflow

An identifying relationship is one where the primary key is populated to the child weak entity as a primary key in that entity. In general though not necessarily a weak entity does not have any items in its primary key other than its inherited primary key and a sequence number.

There are two types of weak entities: The latter represents a crucial type of normalizationwhere the super-type entity inherits its attributes to subtype entities based on the value of the discriminator.

Complete subtype relationship, when all categories are known. Incomplete subtype relationship, when all categories may not be known. The standard example of a complete subtype relationship is the party entity. When sub-type relationships are rendered in a database, the super-type becomes what is referred to as a base table.

The sub-types are considered derived tables, which correspond to weak entities. The discriminator of a weak entity set is a set of attributes that allows this distinction be made.

  • Weak entity
  • Difference between Strong Entity and Weak Entity

It is also called as the Partial key of the entity set. The primary key of a weak entity set is formed by the primary key of the strong entity set on which the weak entity set is existence dependent plus the weak entity sets discriminator.

The relationship between weak entity and strong entity set is called as Identifying Relationship.

Difference Between Strong and Weak Entity

In example, loan-payment is the identifying relationship for payment entity. A weak entity set is represented by doubly outlined box. Here double lines indicate total participation of weak entity in strong entity set it means that every payment must be related via loan-payment to some account.

The arrow from loan-payment to loan indicates that each payment is for a single loan.

difference between strong and weak relationship database

The discriminator of a weak entity set is underlined with dashed lines rather than solid line. Let us consider another scenario, where we want to store the information of employees and their dependents. The every employee may have zero to n number of dependents.

difference between strong and weak relationship database

Relation The relation between two strong entities is denoted by a single diamond simply called relationship. The relationship between a weak and a strong entity is denoted by Identifying Relationship denoted with double diamond. Participation Strong entity may or may not have total participation in the relationship.

Weak entity always has total participation in the identifying relationship shown by double line.

difference between strong and weak relationship database

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.

Database [ DBMS ] - STRONG entity Vs WEAK entity

It indicates that each entity in a strong entity set can be uniquely identified. Set of similar types of strong entities together forms the Strong Entity Set. A strong entity holds the relationship with the weak entity via an Identifying Relationship, which is denoted by double diamond in the ER diagram. On the other hands, the relationship between two strong entities is denoted by a single diamond and it is simply called as a relationship.

Let us understand this concept with the help of an example; a customer borrows a loan. Here we have two entities first a customer entity, and second a loan entity.