attributes

• property or characteristics of an entity or relationship
• essentially represent the columns

Types of Attributes in DBMS

Simple Attribute

• Cannot be divided further.
• Represents a single piece of information.
• Example: Age, Gender.
  Composite Attribute
• Can be divided into sub-parts with individual meanings.
• Useful for grouping related information.
• Example: FullName → FirstName, LastName.
  Single-Valued Attribute
• Holds one value for each entity instance.
• Simple and common in most tables.
• Example: SocialSecurityNumber.
  Multi-Valued Attribute
• Can store multiple values for a single entity instance.
• Often requires separate tables in normalization.
• Example: PhoneNumbers → Home, Work.
  Derived Attribute
• Values computed from other attributes.
• Not stored in the database to save space.
• Example: Age derived from DOB.
  Complex Attribute
• Combines multi-valued and composite attributes.
• Used to represent hierarchical or nested data.
• Example: Address → {Street, City, Country}.
  Stored Attribute
• Values explicitly stored in the database.
• Acts as the base for derived attributes.
• Example: DOB stored, Age derived.
  Key Attribute
• Uniquely identifies an entity in a table.
• Essential for primary keys and relationships.
• Example: StudentID, EmployeeID.
  Null Attribute
• Represents unknown or missing data.
• Does not contribute to computations.
• Example: MiddleName if not applicable.
  Descriptive Attribute
• Provides additional information about a relationship.
• Enhances the semantics of the data.
• Example: EnrollmentDate in a Student-Course relationship.
  Prime Attribute

• An attribute that is part of a candidate key in a relational schema.
• These attributes help in uniquely identifying records within a table.
• Prime attributes are critical in ensuring the uniqueness and integrity of a table’s data.

• These attributes are involved in enforcing primary keys or candidate keys.
• In a Student table, if StudentID is the primary key, then StudentID is a prime attribute.
• If a composite key {StudentID, CourseID} is used, both StudentID and CourseID are prime attributes.