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Untyped Relational Calculus (URC)


The truth conditional representation is domain independent. The expressions (predicate and argument names) that appear in the representation have no particluar significance in the current database by themselves. To produce a suitable query, the notions used must be mapped to relevant fragments of a relational calculus query that is appropriate for the current database. This is done using information in the Extended Data Model (EDM). The most convenient relational calculus to produce at this stage is the Universal Relational Calculus. (This is also called the Untyped Relational Calculus in some reports on Squirrel.)

The expression:

is a representation of:

As can be seen, there is some redundancy in this query, as a result of the simple EDM inspired translation. This redundancy is removed later by some general optimisation strategies.

Chris Fox, September 1995