E-R and EER Models: Basic Concepts

1. Enterprise

Enterprise refers to any kind of organization.

Ex. Colleges, schools, banks, any company etc.

2. Entity

Entity refers to an “object” or “thing” in real world. Object may be any person, place, event etc.

Ex. Students of colleges and schools, loans in banks, employees in any company etc.

3. Attributes

These are the characteristics of any entity.

Ex.,

1. A student  can be  described  by  his name,  age,  address,  height, class  etc.
2. Loans can be described by their types such as house loan, car loan etc.
3. Employees in any company can be described by their Employee ID, name, department, designation etc.
4. A car can be described by his color, model, company etc.

4. Value

Value is the information or data which is stored in attributes of any entity.

5. Entity Sets

All the entities having same attributes make an entity set.

6. Domain

Domain or value set is the set of all values or information about any attribute.

Ex. Consider  the  student table  shown  in Figure  2.1.  It describes  the  basic concepts.

• Enterprise : Here, enterprise is college where students are studied.
• Entity : Here, entity refers to  any single student  with all his values.

Ex.

• Attributes : The students are described by Registration , Name, Age, Branch, Semester, Phone No. These are  the attributes of  students.
• Value : The values are 1A1, 21, Civil, Gaurav, 90091, 5^th etc. 
• Entity Set : All students are described by same set of So, all these students combine together to make an entity set “Student Information”.
• Domain : (Value set) for, attribute, Name it is John, Gaurav, Vivek, Amit, Dheeraj and for  Age,  it  is 20,  19,  21, 22.

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