Associate Entity in Simple M:M
Relational Database does not support Many-To-Many relationships that happen frequently in the real time Business Process Workflow. To avoid this RDBMS limitation, we need to define a Common Entity and map the attributes into two or more different entities. This Common Entity is called Associate Entity.
An instance, an I.T. Company Technical Department is formed with many Employees. Each Employee is assigned in one or many Projects.
When, you focus the diagram from Left to Right side, the diagram representing that an Employee may be assigned in one or many Projects by representing the Connectivity and Cardinality of Relationship Optional Symbol.
When, you focus the diagram from Right to Left side, the diagram representing that Every Project must be operate by one or more Employees by representing the Connectivity and Cardinality of Relationship Mandatory Symbol.
These Employee and Project Entities are produces Data Redundant, when many Employees are assigned in more than one Projects and it is difficult to maintain Project Start Date, Project End Date, Employee Assignment Start Date and Employee Assignment End Date.
Associate Entity Concept is helps to eliminate Data Redundant that define with Composite Primary Key and map Employee and Project entities Primary Key Attributes. Associate Entity Name may be a combination of entities name with XRef word. XRef word is determining (X) Natural Join Dependency (Ref) Reference Entity Type.
This re-designed diagram is representing that an Employee may be assigned in Zero, One or Many Projects and every Project must be operate by One or Many Employees by representing the Connectivity and Cardinality of Relationship Mandatory Symbol.
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