Identifying and Non Identifying Relationships

Identifying Relationships
 
An identifying relationship is a relationship between two entities in which an instance of a child entity is identified through its association with a parent entity, which means the child entity is dependent on the parent entity for its identify and cannot exist without it. In an identifying relationship, one instance of the parent entity is related to multiple instances of the child.

ERWin draws, in I.E. notation, an identifying relationship line as a solid line with crows feet.

Note: ERWin automatically migrates primary key attributes from a parent entity to a child entity, so you do not need to enter any foreign keys in the child.

 Course Example 12
Non-identifying Relationships

A non-identifying relationship is a relationship between two entities in which an instance of the child entity is not identified through its association with a parent entity, which means the child entity is not dependent on the parent entity for its identify and can exist without it. In a non identifying relationship, one instance of the parent entity is related to multiple instances of the child.
You can use ERWin to create these two types of non identifying relationships:

You can also use non-identifying relationships to create recursive relationships.
Note: ERWin automatically migrates primary key attributes from a parent entity to a child entity, so you do not need to enter any foreign keys in the child.

Optional non-identifying relationship
 
In an optional non-identifying relationship, the attributes that are migrated into the non-key area of the child entity are not required in the child entity. This means that nulls are allowed in the foreign key. ERWin draws an optional non-identifying relationship differently depending on the notation for your diagram:

I.E. notation draws a dashed line with a cross and a circle on the parent end. The child end indicates the cardinality with:

  • crows feet with a cross and a circle, as shown below (Zero, one or more)
  • crows feet with a cross (One or more)
  • a cross and a circle (Zero or one)
  • a dashed line (Exactly n)
 Course Example 13
Mandatory Non-Identifying Relationship
 
In a mandatory non-identifying relationship, the attributes that are migrated into the non-key area of the child entity are required in the child entity. This means that the foreign key cannot be null. ERWin draws a mandatory non-identifying relationship differently depending on the notation for your diagram:

I.E. notation draws a dashed line with a cross on the parent end. The child end indicates the cardinality with:

  • crows feet with a cross and a circle, as shown below (Zero, one or more)
  • crows feet with a cross (One or more)
  • a cross and a circle (Zero or one)
  • a dashed line (Exactly n)
 Course Example 14

Symbols
Course Example 15