Domain relational calculus

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In computer science, domain relational calculus (DRC) is a calculus that was introduced by Edgar F. Codd as a declarative database query language for the relational data model.

In DRC, queries have the form:

<math> {<X1, X2, ...., Xn> | p(<X1, X2, ...., Xn>) } </math>

where each X_i is either a domain variable or constant, and p(<X1, X2, ...., Xn>) denotes a DRC formula. The result of the query is the set of tuples X_i to X_n which makes the DRC formula true.

This language uses the same operators as tuple calculus; Logicial operators ∧ (and), ∨ (or) and ¬ (not). The existential quantifier (∃) and the universal quantifier (∀) can be used to bind the variables.

Examples

Let A,B1,C mean Rank, Name, ID and D,E,F to mean Name, DeptName, ID

Find all captains of the starship USS Enterprise:

• {<A, B1, C> | <A, B1, C> in Enterprise ∧ A = "Captain" }

In this example, A,B1,C denotes both the result set and a set in the table Enterprise.

Find Names of Enterprise crewmembers who are in Stellar Cartography:

• {<B1> | ∃ A,C ( <A,B1,C> in Enterprise ∧ ∃ D,E,F(<D,E,F> in Departments ∧ F = C ∧ E = "Stellar Cartography" ))}

In this example, we're only looking for the name, so <B1> denotes the column Name. F = C is a requirement, because we need to find Enterprise crew members AND they are in the Stellar Cartography Department.

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