This content originally appeared on DEV Community and was authored by Jaimin Bariya
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 Employee → Project 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.
This content originally appeared on DEV Community and was authored by Jaimin Bariya
Jaimin Bariya | Sciencx (2024-09-11T12:12:42+00:00) Minimization of ER Diagrams. Retrieved from https://www.scien.cx/2024/09/11/minimization-of-er-diagrams/
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