# Relational Calculus

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## What Does Relational Calculus Mean?

Relational calculus is used with a non-procedural declarative query language in which the user is not concerned with the procedure to obtain outputs. The user only provides the requirements, and the output is provided without knowing the retrieval technique. Relational calculus is mainly used to measure the selective power of relational languages.

## Techopedia Explains Relational Calculus

Relational calculus is largely based on the popular propositional calculus and predicate calculus, the calculus which calculates with declarations and sentences. The concept of relational calculus was developed by Edgar F. Codd. In relational calculus, a query is expressed as a formula which is comprised of a number of variables and an expression consisting of these variables. Compared to the human-database interface, relational calculus takes a completely different approach by only querying users about the desired result. The sentences are far simpler and specifically refer to the database relations and values in relational calculus.

There are two categories of relational calculus: tuple relational calculus and domain relational calculus. Tuple relational calculus specifies to choose the tuples (ordered lists of elements) in a relation and can choose tuples with range of tuples or values for specific values. The resulting relation could have one or more tuples. In the case of domain relational calculus, it makes use of the list of attributes that need to be chosen from the relation based on the conditions. In other words, the difference between tuples relational calculus and domain relational calculus is that domain relational calculus selects the attributes and not the whole tuples like the tuples relational calculus.