Specifying queries as relational expressions

SQUARE (Specifying Queries As Relational Expressions) is a set oriented data sublanguage for expressing queries (access, modification, insertion, and deletion) to a data base consisting of a collection of time-varying relations. The language mimics how people use relations or tables to obtain information. It does not require the sophisticated mathematical machinery of the predicate calculus (bound variables, quantifiers, etc.) in order to express simple references to tables. However, the language has been shown to be complete, i.e., any query expressible in the predicate calculus is expressible in SQUARE.