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DBMS ER Model
DBMS Relational Data Model
ER Model: Entity Relationship Diagram (ERD) with Examples
ER model stands for Entity-Relationship Model or Entity Relationship Diagram (ERD).
What is the ER Model?
ER model stands for Entity-Relationship Model. ER modelling is a high stage conceptual data model promote to simplify database design. A conceptual data model is a set of concepts that define the mechanism of a database and the related retrieval and update transactions of the database. It is independent of any specific database management system (DBMS) and hardware platform.
The ER model is also represented as a logical representation of records for a company. It was developed to simplify database design using allowing specification of a company schema, which defines the overall logical architecture of a database. It is a top-down method for database design.
The overall logical architecture of a database can be represented graphically by an Entity-Relationship Diagram as follows:
History of ER Models
ER diagram is a visual device that is helpful to describe the ER model. It was suggested by Peter Chen in 1971 to construct a uniform meeting which may be utilized for a relational database and network. ER Model is a powerful and standard technique of communication among various designers, programmers, and end-users who generally tend to view records and its use in different methods. It is a non-technical method, which is loose from ambiguities and provides a standard and a logical process of visualizing the record.
Features of ER Model
- This model is widely used to create the initial layout of the database.
- This model supports a collection of fundamental ideas that can be implemented in a database framework.
- It represents records as a set of entities, attributes, and relationships.
- It supports the graphical or conceptual file of the database design.
What is an Entity-Relationship Diagram?
An ERD or Entity-Relationship Diagram is the graphical description of objects (entities) and the relationship between those entities in the database. In other words, the ER diagram defines the logical architecture of the database. It contains many specific symbols, and its definitions create this structure unique.
In the figure, an ER diagram display the relationship between the entity sets EMPLOYEE and POSITION. The relationship set is known as DUTY_ALLOCATION, and its attributes are Date and Shift.
Data for an ER relationship might be represented by using several tables. The represented Duty_Allocation among the entities EMPLOYEE and POSITION is represented by using three tables, as shown in fig:
Make an ER diagram for the company database with the subsequent description:
- The company is formulated in the department. Each department has a particular name and the particular number. The department may have several locations.
- A department control several projects, every of which has a particular name, a particular number, and the single location.
- We save each employee name, social security number, address, and salary. An employee is designate to one department but may work on different projects, which are not essentially composed by similar departments.
- We need to hold record of the dependents of every employee for insurance objectives. We preserve each dependent’s name, age, and relationship to the employee.
Hence to make the ER diagram, follow the two steps:
- Identify all entities and attributes of the given problem.
- Identify the relationship between the entities and constraints on the entities and implement them.
ER Diagrams Notations
The database can be defined using the notations. In the Entity-Relationship diagram, many notations are used to describe the cardinality. These notations which are as follows: