Reduction of ER Diagram to Tables

For converting strong entity type there are some points that should be kept in mind.

• Entity type becomes a table in it.

A Single - Valued Attribute becomes a column for a table.

Derived Attribute are ignored and not considered in table.

Composite Attribute are represented by components

Multivalued Attributes are represented by Separate table.

• A key attribute of the Entity type becomes the Primary Key of the table. Entity-Attributes

• Here Address is Composite Attribute.

• Years-Of-Service is DSerived Attribute

• Skillset is a Multivalued Attribute : We have to make separate table but remember there should be relationship between an employee table and skill set table.

So the Relational Schema and Employee Skill set table is:>

Employee(E#, Name, Door_No,Street, city, pincode, date_of_joining)

Employeeskillset(E#, Skill)


As we saw E# has to be primary key for employee table hey uniquely identify an entity and employee skill set has skill which came from skill set (multi valued).

So to create a relationship between these two table we use E# i.e Employee Code in EmployeeSkill set table as a "foreign key" which implements Referential Integrity.


Converting Weak Entity Types:

• Weak Entity type are converted into table of their own, with the primary key of the strong entity acting as a foreign key in the table.

• This ForeignKey along with the key of the weak entity from the composite primary key of this table.

• The Relational Schema:



Dependent(E#, Dependent_ID,Name, Address) Relational_schema-1

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