Database Relation Model: Attributes

Relation Model: Attributes

• Definition:

  • An attribute is a property or characteristic of a relation (table) in a relational database.

• Characteristics:

  • Each attribute has a unique name within a relation.
  • Attributes can be of various data types (e.g., integer, string, date).
  • The order of attributes in a relation is not significant, but it is typically displayed in a defined sequence.

• Types of Attributes:

  • Simple Attribute:
    • Cannot be divided further (e.g., age, first name).
  • Composite Attribute:
    • Can be divided into smaller sub-parts (e.g., full name can be split into first name and last name).
  • Derived Attribute:
    • Its value is calculated from other attributes (e.g., age derived from birth date).
  • Multi-valued Attribute:
    • Can hold multiple values for a single entity (e.g., a person having multiple phone numbers).

• Constraints on Attributes:

  • Domain Constraints: Define the permissible values for an attribute (e.g., age must be a non-negative integer).
  • Null Constraints: Specify whether an attribute can have a null value (i.e., no data).
  • Unique Constraints: Ensure that all values in an attribute are unique across tuples (e.g., social security number).

• Key Attributes:

  • Primary Key: An attribute (or a set of attributes) that uniquely identifies each tuple in the relation.
  • Foreign Key: An attribute that creates a link between two relations, referencing the primary key of another relation.

• Importance:

  • Attributes are essential for defining the structure of a relation and for ensuring data integrity and retrieval efficiency in a database.

Definition of Attributes

• Attributes are properties or characteristics of a relation (table) in a relational database.

Characteristics of Attributes

• Each attribute must have a unique name within a relation to ensure clarity.
• Attributes can utilize various data types such as integers, strings, and dates, enhancing flexibility.
• The sequence of attributes in a relation is not significant, but a defined order is typically displayed for user convenience.

Types of Attributes

• Simple Attribute: Cannot be divided further, examples include age and first name.
• Composite Attribute: Can be subdivided into smaller parts, such as full name being split into first name and last name.
• Derived Attribute: Value is calculated from other attributes; for example, age can be derived from birth date.
• Multi-valued Attribute: Can hold multiple values for a single entity, like a person with multiple phone numbers.

Constraints on Attributes

• Domain Constraints: Define acceptable values for an attribute, ensuring data validity; for instance, age must be a non-negative integer.
• Null Constraints: Specify whether an attribute can hold a null value, representing the absence of data.
• Unique Constraints: Ensure all values in an attribute are distinct across tuples, such as a social security number being unique.

Key Attributes

• Primary Key: An attribute (or a set of attributes) that uniquely identifies each tuple within a relation.
• Foreign Key: An attribute that links two relations by referencing the primary key of another relation.

Importance of Attributes

• Attributes are crucial for defining the structure of a relation, ensuring data integrity, and facilitating efficient data retrieval in a database.