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DBMS Relational Model concept

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Relational Model concept

Relational model can represent as a table with columns and rows. Each row is known as a tuple. Each table of the column has a name or attribute.

Domain: It contains a set of atomic values that an attribute can take.

Attribute: It contains the name of a column in a particular table. Each attribute Ai must have a domain, dom(Ai)

Relational instance: In the relational database system, the relational instance is represented by a finite set of tuples. Relation instances do not have duplicate tuples.

Relational schema: A relational schema contains the name of the relation and name of all columns or attributes.

Relational key: In the relational key, each row has one or more attributes. It can identify the row in the relation uniquely.

Example: STUDENT Relation

Ram 14795 7305758992 Noida 24
Shyam 12839 9026288936 Delhi 35
Laxman 33289 8583287182 Gurugram 20
Mahesh 27857 7086819134 Ghaziabad 27
Ganesh 17282 9028 9i3988 Delhi 40
  • In the given table, NAME, ROLL_NO, PHONE_NO, ADDRESS, and AGE are the attributes.
  • The instance of schema STUDENT has 5 tuples.
  • t3 = <Laxman, 33289, 8583287182, Gurugram, 20>

Properties of Relations

  • Name of the relation is distinct from all other relations.
  • Each relation cell contains exactly one atomic (single) value
  • Each attribute contains a distinct name
  • Attribute domain has no significance
  • tuple has no duplicate value
  • Order of tuple can have a different sequence

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