Domain calculus Details, Meaning Domain calculus Article and Explanation Guide

Domain calculus Guide, Meaning , Facts, Information and Description

In computer science, domain relational calculus is a calculus that was introduced by Edgar F. Codd as part of the relational model in order to give a declarative database query language for this data model.

A DRC Query has the form:

where each X_i is either a domain variable or constant, and p() denotes a DRC Formula. The result of the query is 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), and we can use the existential quantifier (∃) and the universal quantifier (∀) to bind the variables.

Here are examples of DRC:

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

Find all Captains of the Enterprise:

{ | in Enterprise ∧ A = "Captain" }

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

Find Names of Enterprise crewmembers who are in Stellar Cartography:

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

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

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Domain calculus Guide, Meaning , Facts, Information and Description

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