Entity Relationship Model

• Is a data model that describes relationships among entities at the conceptual level with the help of ER diagrams.

  The Entity Relationship Model (ERM)
• Is a diagram that depicts an entity relationship model’s entities, attributes, and relations.

  The Entity Relationship Diagram (ERD)
• An entity is represented in the ERD by a?

  Rectangle
• An entity is represented in the ERD by a rectangle, it is also known as?

  Entity Box
• The name of the entity, a noun, is written in the center of the rectangle.
• The entity name is generally written in capital letters and in singular form.

• Each row in the relational table is known as an entity instance or entity occurrence in the ER model.
• A collection of similar entities is known as?

  Entity Set
• Describe associations among data.

  Relationships
• The type of relationship between entities.

  Connectivity
• Connectivity is represented in an ERD by a?

  Line
• The name of the relationship is usually an active or passive verb.
• ER Model Notations

  1. Chen Notation
  2. Crow's Foot Notation
• Chen Notation:

  • Relationships are represented by a diamond connected to the related entities through a relationship line.
  • The relationship name is written inside the diamond.

  
• Crow's Foot notation:

  • Entities are connected by lines and symbols at either end.
  • Describes the cardinality of the relationship between the entities.

  
• Describes particular characteristics of the entity.

  Attributes
• In the original Chen notation, attributes are represented by what shape?

  Ovals
• The Original Chen Notation

  Ovals are connected to the entity rectangle with a line. Each oval contains the name of the attribute it represents. The entity identifier is mapped as the table's primary key and is underlined.

  
• Are used to mark the primary and foreign keys.

  PK and FK
• • In the Crow’s Foot notation, the attributes are written in the attribute box below the entity rectangle.
  • Required attributes are in boldface.

  
• How is the entity name generally written?

  Capital letters and Singular Form
• Active and passive verb are used in?

  The name of the relationship