Relational Calculus and Algebra
- Relational Algebra - Very useful for representing execution plans
- Relational Calculus - Lets the user describe what they want rather have to compute it (non operational or declarative, relational calculus takes its name from predicate calculus.
There are 2 different variations of relational calculus
- Domain Calculus - specification of formal properties for different data types, used for describing data, introduced by Michel Lacroix and Alain Pirotte.
- Tuple Calculus - querying and checking formal properties of stored relational data.
A certain order is always explicitly specified in a relational algebra expression, and a strategy for evaluating the query is implied.
In relational calculus, there is no description of how to evaluate a query; a relational calculus query specifies what is to be retrieved rather than how to retrieve it.
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