Entity Relation Model

Question 1

History of ER

Answer 1

→ proposed by Peter Chen in 1976
→ used to visually represent the structure of a database, making it easier for designers to understand and communicate the requirements of a system

Question 2

ER diagram

Answer 2

→ Is a Visual representation of a database’s structure.
→ Represents tables (entities) and their relationships.
→ Utilizes symbols for entities, attributes (columns), and relationships.
→ Keys, including primary and foreign keys, connect tables.
→ Each column is represented by a key.
→ Symbols ensure consistency and uniqueness for each table.
→ Facilitates team collaboration by providing a visual blueprint.
→ Shareable documents that enhance teamwork and understanding.

Question 3

Advantages of ER Diagram

Answer 3

→ Clarity and Simplicity
→ Shareability
→ Ease of Modification
→ Expandability
→ Comprehensive Overview

Question 4

Components of ER Diagram

Answer 4

→ Entities
→ Attributes
→ Relationships

Question 5

Entities

Answer 5

→ An entity is a real-world object, concept, or thing that is distinguishable and identifiable. It can be presented with specific attributes.
→ Entity Set: An entity set is a collection or grouping of similar entities. The entity set is the set of all entities that share the same set of attributes. (the entire table)
→ Strong Entity: is a type of entity that has a key Attribute. Strong Entity does not depend on other Entity in the Schema. It has a primary key, that helps in identifying it uniquely. (has a primary key)
→ Weak Entity: is a type of entity that does not have a primary key that uniquely identifies it on its own. It relies on another entity, known as the owner or parent entity, for identification. (no primary key)

Question 6

Strong Entity Set vs Weak Entity Set

Answer 6

→ Strong Entity Set

Has a primary key

Relations can be created between entities

Normalization (ability to create small tables)

Hierarchy data set

Partitional relations (Relationships can be established independently without relying on other entities.)

Independent

→ Weak Entity Set

No primary key

Weak relations

Represented in bigger tables

Non-hierarchical

Optional relations

Dependent

Question 7

Attributes

Answer 7

are the properties that define the entity type.

Question 8

Cardinality/Relationships

Answer 8

→ Optional Relationships:
* Optional: Entities in the relationship may or may not participate.
* Mandatory: Entities in the relationship must participate.
→ Partitional Relationships:
* One-to-One: Each entity in the relationship is related to only one other entity.
* One-to-Many: An entity in one set is related to multiple entities in another set.
* Many-to-Many: Entities in both sets can be related to multiple entities in the other set.

→ If a many-to-many relation is created, it’d create a weak entity set: Many-to-many relationships often require the introduction of a junction or associative entity, which can be considered a form of a weak entity set.

Question 9

ER Notations

Answer 9

→ Strong Entity: rectangle
→ Weak Entity: double rectangle
→ Attribute: oval
→ Relationship: diamond
→ Weak Relationship: double diamond
→ Mandatory: small line
→ Optional: small circle
→ One: small line
→ Many: 3 lines

Question 10

Steps to Create an ERD

Answer 10

1. Entity Identification
   
   2. Relationship Identification
   3. Cardinality Identification
   4. Identify Attributes
2. Create ERD

Question 11

Creating Effective ER Diagrams

Answer 11

→ Create strong entity sets
→ Use easy-to-read naming and symbols
→ Clear symbols
→ Don’t connect tables with same keys
→ Synchronization