DIFFERENT TYPE OF RELATION TWO TYP OF RELATION

DIFFERENT TYPE OF RELATION  

TWO TYP OF RELATION 

Relational model provides to type relations they are as following 

1- basic relation

2- derived relation

1- basic relation - at any given instant of time a given relations is called the base relation.

2- derived relation We can derive relations for base relations and relations that is bring derived from base relation is called the derived relation.

for example

if we take a relations branch with attributes branch_ name, branch_city and assets.

each attribute has appropriate domains.

Thus we can

represent this relations branch branch name City e assets let's its any given

instant time the branch relations look like

                           THE BRANCH  TABLE

NAME	CITY	ASSETS
downtone	Brooklyn	400000
Red wood	Palo	820000
Mainus	Rye	200000
Perryridge	Horsenake	400080
Tollly	Bhunhat	214000

If there is any

derived relations say branch view which give the assets as name city and

assets, where name is derived from branch name city is derived from branch city

and assets is assets 1000000. that derived relations would looks like table.

                                THE DERIVED BRANCH – VIEW 

NAME	CITY	ASSETS
downtone	Brooklyn	200000
Red wood	Palo	500000
Mainus	Rye	200302
Perryridge	Horsenake	4000
Tollly	Bhunhat	210000

Derived relations

of view or directly depend on the basic relation. as if we changing basic

relations these changes directly reflect in derived relations.

For example we

delete the tuple representing branch Perriyridge and its information then

resultant relations we are left which will be as follows:-

               THE BRANCH RELATION

NAME	CITY	ASSETS
downtone	Brooklyn	400000
Red wood	Palo	820000
Mainus	Rye	200000
Perryridge	Horsenake	400080
Tollly	Bhunhat	214000

                         THE BRANCH VIEW

NAME	CITY	ASSETS
downtone	Brooklyn	200000
Red wood	Palo	500000
Mainus	Rye	200302
Perryridge	Horsenake	4000
Tollly	Bhunhat	210000

So from these

examples we can conclude

that -

1- view reflect the

change in the basic relations directly

2- attributes in

the view can be defined as any valid relations expression relation expression

may include any attribute values that correspond to be tuple and any constant

as per the need.

3- number and name

of attributes in view are independent to that of relations.

One major

difference between relation is to have a set of tuple but views to not. you

just uses the The tuples of the base relations at that instant of time. in case

of relations the definition of the relation as The tuples are stored. while in

will facilitate the applications without putting load over the database.

case of view only the definitions of view for stored , so having some useful we

Derived relations

i.e view not necessarily user the attributes of single relations. it may have

relation expression that uses some attitude one relations and some of other

included and the rule applied over them is the same.

there is no specifications of the number of relations that the expression may