Wednesday, 5 February 2020

Relational Language and Database Design

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Relational Language and Database Design


Relational algebra is a procedural language. It provides a collection of operations to manipulate
relations. It supports the notion of a query which is a request to retrieve information from a
database. The relational algebra data operations and their corresponding operators are:
Basic Operations:
Selection Select Operator ( )
Projection Project Operator ( )
Cross-product Cartesian product (×)
Union Operator ( )
Set Difference Difference Operator (–)

Notes Additional Operations:
Intersection Intersect Operator ( )
Join Join Operator ( ?? )
Division Division operator ( )
Rename Rename operator ( )
Here, selection, projection, rename are unary operators and other operators are binary.


Binary operations: Operations which operate on two relations.
ER model: The entity-relationship (ER) data model allows us to describe the data involved in
real-world enterprise in terms of objects (entities) and their relationships, and is widely used to
develop an initial database design.
Relational algebra: The Relational Algebra which is an algebraic notation, where queries are
expressed by applying specialized operators to the relations.
Relational calculus: The Relational Calculus which is a logical notation, where queries are
expressed by formulating some logical restrictions that the tuples in the answer must satisfy.
Unary operation: Operations which operates on only one relation.

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