Domain calculus
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 Xi to Xn 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.
Work In Progress
, feel free to add.