Database Management Systems (dbms)

Attributes that are not divisible are called simple or atomic attribute.

Eg: Emp_No

Composite attribute

Can be divided in a smaller part which represent more basic attributes with independent meaning of their own.

Eg: Name (First Name, Mid Name, Last Name)

Type of attributes

• Multi-valued attribute

In some case an attribute can have a set of values for the same entity such attributes are called multi-valued attributes.

Eg. Degree of a person , Qualification

• Derived attribute
• An attribute whose value can be calculated from related attribute values

Eg: Age (Using Date of Birth) .

Years Employed (Using Employed Date) .

Relationship

• Relationship

A meaningful association between entities.

Eg:

Student follows courses

Employee works for department

Relationship

• Degree of a Relationship

The degree of the relationship type is no. of participating entity types .

• Unary Relationship
• Relationship between the instances of a single entity type.

E.g.: person is married to a person (1:1)

Employee manages Employees (1:M)

• Binary Relationship
• Relationship between the instances of two entity types.

Degree = 2;

Student
Courses
follows
Manages
Employee

Relationship

• Degree of a Relationship
• Ternary Relationship

A simultaneous relationship among the instances of three entity type.

Supplier
Project
supplies
Part
Degree = 3 ,Ternary Relationship