Lesson 3: Relational Data Model

• Relational Data Model


  Represent data in the form of tables, where a named, two-dimensional table is called a relation. Each relation consists of named columns (attributes) and an arbitrary number of unnamed rows (records).
• Classification of Attributes

  • Required vs. Optional Attributes
  • Simple vs. Composite Attributes
  • Single-valued vs. Multivalued Attributes
  • Stored vs. Derived Attributes
  • Identifier
• Required vs. Optional Attributes

  • Required attributes must be provided, optional attributes may be left blank
• Simple vs. Composite Attributes

  • Simple attributes have a single value, composite attributes have multiple values
• Single-valued Attribute


  • StudentID
  • STudName
  • BirthDate
• Multivalued Attribute


  • ContactNo
• Stored vs. Derived Attributes

  • Stored attributes are directly stored in the database, derived attributes are calculated from other attributes
• Stored Attribute


  • StudentID
  • STudName
  • BirthDate
• Derived Attribute


  • Age
• Identifier


  • An attribute or combination of attributes that uniquely identifies each row in a relation. Must not change in value, must not be null, and must be unique.
• Properties of a Relation


  • Unique name

  2. No multivalued attributes

  3. Each row is unique

  4. Each attribute has a unique name

  5. Sequence of columns and rows is insignificant
• Primary Key


  An attribute or combination of attributes that uniquely identifies each row in a relation
• Foreign Key


  Attribute used to establish the relationship between two tables, pointing to the primary key of another table
• Composite Key


  A key that consists of more than one attribute
• Cust_ID is a foreign key in ORDER, allowing an order to be associated with a particular customer
• Integrity Constraints


  • Domain Constraints
  • Entity Integrity
  • Referential Integrity
• Integrity Constraints


  Rules limiting acceptable values and actions to facilitate maintaining the accuracy and integrity of data
• Entity Integrity


  Ensures that every relation has a valid primary key
• Referential Integrity


  Rule that maintains consistency among the rows of two relations, where a foreign key value must match a primary key value or be null
• Domain Constraints 


  a domain definition consists of domain name, meaning, data type, size and allowable values for the domain values
• Domain Constraints


   it is an attribute that specifies all the possible values that the attribute can hold like integer, character, date, time, string, etc.
• Domain Constraints


  are user-defined columns that help the user to enter the value according to the data type.