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Jaimin Bariya
Jaimin Bariya

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Minimization of ER Diagrams

Minimization of ER Diagrams

Minimizing ER diagrams involves simplifying the design to reduce complexity while retaining essential information. Here are the key steps with detailed examples:

1. Remove Redundant Relationships

Explanation: Redundant relationships are those that can be inferred from other existing relationships, adding unnecessary complexity.

Before:

Entity 1 Relationship Entity 2 Description
Employee works in Department An employee works in a department.
Department manages Project A department manages a project.
Employee works on Project An employee works on a project.

After:

Entity 1 Relationship Entity 2 Description
Employee works in Department An employee works in a department.
Department manages Project A department manages a project.

Note: Removed the direct EmployeeProject relationship because it is implied through the Department relationship.


2. Merge Entities with One-to-One Relationships

Explanation: Entities that have a one-to-one relationship and share attributes can be merged into a single entity to simplify the design.

Before:

Entity Attributes
Employee EmployeeID, Name, Address
EmployeeDetails EmployeeID, Salary, DateOfJoining

After:

Entity Attributes
Employee EmployeeID, Name, Address, Salary, DateOfJoining

Note: Merged EmployeeDetails into Employee because they have a one-to-one relationship.


3. Simplify Weak Entities

Explanation: Weak entities that have total participation in a relationship with a strong entity can often be merged into the strong entity to streamline the design.

Before:

Strong Entity Weak Entity Attributes
Order OrderItem OrderID, OrderDate, ItemID, Quantity, Price

After:

Entity Attributes
Order OrderID, OrderDate, Items (ItemID, Quantity, Price)

Note: Simplified OrderItem by integrating it into Order as a collection of items.


4. Remove Multi-Valued Attributes

Explanation: Multi-valued attributes (those that can have multiple values) should be moved to a separate entity to adhere to the principle of atomicity.

Before:

Entity Attributes
Employee EmployeeID, Name, PhoneNumbers (multi-valued)

After:

Entity Attributes
Employee EmployeeID, Name
PhoneNumber PhoneNumberID, EmployeeID, PhoneNumber

Note: Moved PhoneNumbers to a separate PhoneNumber entity to handle multiple values.


5. Remove Derived Attributes

Explanation: Derived attributes, which can be calculated from other attributes, should be removed from the schema to avoid redundancy.

Before:

Entity Attributes
Person PersonID, Name, DateOfBirth, Age (derived)

After:

Entity Attributes
Person PersonID, Name, DateOfBirth

Note: Removed Age from Person since it can be calculated from DateOfBirth.


6. Use Generalization/Specialization

Explanation: Generalization combines similar entities into a single generalized entity, while specialization divides a generalized entity into more specific entities.

Before:

Entity Attributes
UndergraduateStudent StudentID, Name, DegreeProgram
GraduateStudent StudentID, Name, ResearchTopic

After:

Generalized Entity Specialized Entities Attributes
Student UndergraduateStudent StudentID, Name, DegreeProgram
GraduateStudent StudentID, Name, ResearchTopic

Note: Generalized Student into a single entity with specialized UndergraduateStudent and GraduateStudent.


Summary

1. Redundant Relationships: Simplified by removing inferred relationships.

2. Merge Entities: Combined one-to-one entities into a single entity.

3. Simplify Weak Entities: Merged weak entities into strong entities where applicable.

4. Multi-Valued Attributes: Moved multi-valued attributes to separate entities.

5. Derived Attributes: Removed derived attributes and calculated them dynamically.

6. Generalization/Specialization: Combined similar entities or created specific entities from a general entity.


Interview Question

How do you handle redundant relationships and entities in ER diagram minimization?

Answer: To handle redundant relationships, identify and remove any that can be inferred from existing ones. For entities, merge those with one-to-one relationships, simplify weak entities with total participation, and manage multi-valued and derived attributes appropriately to create a streamlined and efficient ER diagram.

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