Question

An expression in the domain relational calculus is of the form:
1. \(\lbrace P(x_1, x_2,..., x_n)|<x_1, x_2,..., x_n>\rbrace\)
2. \(\lbrace x_1, x_2, ..., x_n | < x_1, x_2, ..., x_n >\rbrace\)
3. \(\lbrace x_1, x_2, ..., x_n | x_1, x_2, ..., x_n \rbrace\)
4. \(\lbrace < x_1, x_2, ..., x_n > | P(x_1, x_2, ..., x_n)\rbrace\)

Answer 1

Correct Answer - Option 4 : \(\lbrace < x_1, x_2, ..., x_n > | P(x_1, x_2, ..., x_n)\rbrace\)

The correct answer is option 4.

•  Domain Relational Calculus

It is a nonprocedural query language equivalent in power to Tuple Relational Calculus. Domain Relational Calculus provides only the description of the query but it does not provide the methods to solve it.

• Relational Calculus,

It is a query is expressed as, { < x1, x2, x3, ..., xn > | P (x1, x2, x3, ..., xn ) }

where, < x1, x2, x3, …, xn > represents resulting domains variables and P (x1, x2, x3, …, xn ) represents the condition or formula equivalent to the Predicate calculus.

∴ Hence the correct answer is { < x1, x2, x3, ..., xn > | P (x1, x2, x3, ..., xn ) } .

•  Tuple Relational Calculus (TRC) :
  • A tuple relational calculus is a non-procedural query language that specifies the tuples in a relation to be selected. It can choose tuples with a range of values, tuples for specific attribute values, and so on. One or more tuples can be found in the resulting relation.
    • Notation :
      {T | P (T)} or {T | Condition (T)}
      -where T is resulting in tuples and P(T) is a condition used to fetch T.
•  Domain Relational Calculus (DRC) :
  • A domain relational calculus selects attributes from a relation based on a conditional list. It's similar to TRC, but instead of selecting entire tuples, it selects attributes.
    • Notation :
      { a1, a2, a3, ..., an | P (a1, a2, a3, ..., an) } 
      Where a1, a2, a3, … an are attributes of the relation and P is the condition.