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Sunday, March 20, 2016

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What are Attributes in DBMS?

Leke Oyetoke - Sunday, March 20, 2016

What are Attributes in DBMS?

Entities are represented by means of their properties called attributes. All attributes have values. For example, a student entity may have name, class, and age as attributes.

There exists a domain or range of values that can be assigned to attributes. For instance, a student's name cannot be a numeric value. It has to be alphabetic. A student's age cannot be negative, etc.

Types of Attributes 

1. Simple attribute: Simple attributes are atomic values, which cannot be divided further. For instance, a student's phone number is an atomic value of 10 digits.

2. Composite attribute: Composite attributes are made of more than one simple attribute. For instance, a student's complete name may have first_name and last_name.

3. Derived attribute: Derived attributes are the attributes that do not exist in the physical database, but their values are derived from other attributes present in the database. For instance, average_salary in a department should not be saved directly in the database, instead it can be derived. For a further example, age can be derived from data_of_birth.

4. Single-value attribute: Single-value attributes contain single value. Example: Social_Security_Number.

5. Multi-value attribute: Multi-value attributes may include more than one values. For instance, a person can have more than one phone number, email_address, etc.

Attribues can be in form of:

1. Simple single-valued

2. Simple multi-valued

3. Composite single-valued

4. Composite multi-valued


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