**2.2 Query**

A select-project query is a tuple < QUA, QUR, QUP,QUD>, where QUA is *Select Clause* of query which contains projected attributes. QUR is the *From Clause* which contains relation of a database D, from which data is to be retrieved. QUP is *Where Clause* which contains conjunctive or disjunctive compare predicates, a compare predicate is of the form *P = a op c*, where *a A {Attributes Set}, op {* ,,,, *}, c* is a constant in a specific domain (Ren et al., 2003), QUD is the *resultant data* of this query. A query can be represented as *π QUA σ QUP (QUR)* in relational algebra.
