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Attributes and Types of Attributes

An attribute is a property or characteristic that describes an entity in a database.

  • Each entity type has a set of attributes that provide specific information about the entity.

Example: For the entity type “Student,” attributes could be “Student ID,” “Name,” “Date of Birth,” and “Course.”

Attributes can be categorized into several types based on their characteristics and the type of data they represent:

  • Atomic (Simple) vs. Composite attributes
  • Single-Valued vs. Multi-Valued attributes
  • Derived vs. Stored attributes
  • Key Attributes
  • Null Attributes

An attribute that cannot be divided into smaller independent attribute is called as atomic attribute.

  • These attributes contain single, straightforward values.
  • They represent the smallest unit of information and are not composed of sub-attributes.

Example:

  • “Age” is a simple attribute because it’s a single value that can’t be broken down into smaller components.
  • “Gender” is another simple attribute that represents a singular value.

An attribute that can be divided into smaller independent attribute is know as composite attribute.

Example:

  • “Full Name” is a composite attribute, which can be divided into “First Name” and “Last Name.”
  • “Address” is another composite attribute that can be broken down into “Street,” “City,” “State,” and “Zip Code.”

An attribute that holds only single value for an entity is known as single valued attribute.

Example:

  • “Age” is a single-valued.
  • “Date of Birth” is another example of a single-valued attribute, as each person has exactly one date of birth.

An attribute that holds multiple values for a single entity is known as multi valued attribute.

Example:

  • “Phone Numbers” is a multi-valued attribute, as a person may have multiple phone numbers (e.g., home phone, work phone, and mobile phone).
  • “Email Addresses” is another example, where a person can have multiple email addresses.

An attribute that can be derived from another attribute is known as Derived Attribute.

  • The value of a derived attribute is not stored in the database.
  • It saves storage space and ensures consistency by deriving data from existing attributes.

Example:

  • “Age” is a derived attribute that can be calculated from the “Date of Birth.”

An attribute that cannot be derived from another attribute is known as Stored Attribute.

  • The values of stored attributes are directly stored in the database tables.

Example:

  • “Date of Birth” is a stored attribute, as the actual value is stored in the database and used to derive the “Age.”
  • “Salary” is another stored attribute.

An attribute that has unique value of each entity is known as key attribute.

  • These attributes hold unique values for each entity, making it possible to identify each entity uniquely.

Example:

  • “Student ID” is a key attribute, as it uniquely identifies each student.
  • “Employee ID” is a key attribute in the employee database, ensuring each employee has a unique ID.

An attribute that do not hold any value for an entity is known as null attribute.

Example:

  • “Middle Name” can be a null attribute if a person doesn’t have a middle name.
  • “Spouse Name” can also be a null attribute for individuals who are unmarried.

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