Wednesday, 6 August 2014

Relational Model | Relational calculas


Relational algebra is concerned with a procedural language in which the user has to write the steps or procedure to obtain the required result.In this the user is not concerned with the detail of how to obtain information.
         In relational calculus the user tell his requirement and the output is available without knowing the method about its retrieval.
a.) It is a non procedural language.
b.) This concept was first expressed by codd. It is based on the predicate calculus.
c.) It is a formal language used to symbolize local argument in mathematics.Proposition specifying a property consist of an expression that names an individual object and an other expression called the predicate,that stands for the property that an individual object possesses.

In relational calculus we can make the following operations
Example-Let x and y are preposition then we can build other preposition like

"Not x"
"x and y"
 "x or y"m and so on.

Consider the following statement

India is a country.
We can write it.
" is a country  (India)"
we can drop is a then preposition will be
" Country (India)"
Finally if we use symbols for both predicates and objects then we can rewrite the statement X (a).Lower case letter denotes the variables beginning letters {a,b,c......}denotes the constants.
Upper case letter denotes the predicate.
P{X} where X is the argument.

It can be categorized into 2 parts:-
1,) Tuple Oriented Relational calculus
2.) Domain Oriented Relational calculus.


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