E-R and EER Models: Entity – Relationship Diagram

E-R diagrams represents the logical structure of a database. Symbols used in E-R diagrams are shown  in Table 2.1.

Examples :

1. Make an E-R diagram having two entity sets, Customer and Item.

Cardinality Ratio is many to many because a customer can buy any number of items and same item can  be purchased by more  that one customer.

2. Make an E-R diagram with entities Customer, Loan and Payment

1. Advantages of E-R model

The major  advantages of  E-R model  are  as follows:

1. Straightforward relation representation: The relation representation of the database model using E-R diagram are relatively more straightforward than other models.
2. Mapping with relational model: It can be easily mapped onto the relational The E-R diagrams used in the E-R model can easily be transformed into relational tables. The entities and attributes of E-R model can easily be transformed into relations (tables) and columns  (fields)  in  a relational  model.
3. Communication tool: It is very simple and easy to understand with a minimum of training efforts Therefore, the model can be used by the database designer to communicate the design  to  the end  user.

4. Design tool: E-R model can also be used as a design plan by the database developer to implement a data  model  in specific  database  management software.
5. Easy conversion to other models: E-R diagrams can be easily converted to a network or hierarchical data model.
6. Graphical representation: E-R model provides graphical and diagrammatical representation of various entities, their attributes and relationships between entities.
7. Easy to modify: Modifications to E-R diagram at later stage is relatively easier than in other models.

2. Limitation of E-R Model

Limitation of E-R Model : E-R model cannot express relationships between relationships. In other words E-R model is not capable to express relationship set between relationship sets.

This limitation  can be  overcome by  using EER  model.

Source: Gupta Satinder Bal, Mittal Aditya (2017), Introduction to Database Management System, 2nd Edition-University Science Press (2017)