Page 109 - DCAP402_DCAO204_DATABASE MANAGEMENT SYSTEM_MANAGING DATABASE

Database Management Systems/Managing Database

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.

6.13 Keywords

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.

6.14 Self Assessment

Choose the appropriate answer:
1. Relational calculus is an alternative to:
(a) Relational algebra
(b) Relational valuation

(c) Related query
(d) Relational calculation
2. QBE stands for
(a) Quick-by-Example

(b) Query-by-Example
(c) Queue-by-Example
(d) Query-by-Expansion
Fill in the blanks:

3. A ............................. is a variable that takes on tuples of a particular relation schema as
values.
4. A ........................formula is defined in a manner that is very similar to the definition of a
TRC formula.
5. The ER model is important for its role in ...............................
6. ............................. represent entity sets.

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