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MAIN PROPERTIES OF RELATION (CHARACTERISTICS OF RELATION)


       MAIN PROPERTIES OF RELATION

CHARACTERISTICS OF RELATION

                                                                                                             THE main fourth main properties of relation as follows –

A.     There are no duplicate tuples

B.     Tuples are unordered top to buttom

C.     Attributes are unordered lift to right

D.    Each tuple contains exactly one of value for each atteibute



There are no duplicate tuplesthis property follows from the fact  that the body of the relation is a mathematical set and does not duplicate element . it is useless to have same SET OF ATTRIBUTES MORE THAN ONES in the given relation. A relation account as  show in table.

SBI  ACCOUNT TABLE

BRANCH NAME

ACCOUNT NO.

BLANCE 

ADDRESS

BHOPAL
2020202020
100000
M.P BHOPAL
JABALPUR
2020101010
10020
MUMBAI
GHANDHI NAGAR
2020303030
100010
GUJRAT


Then it becomes the fact of the relation. Repeating the same would neither make any sense nor affect the truthness of this fact.
This property of relation clearly says that relation is different from table. It is so because table allow the duplication of record while relation does not. 

A.    Tuples are unordered top to buttom this property follows from the fact  that the body of the relation is a mathematical set. Set in mathematics are not ordered. Relation are independent of the order of tuples  in it. Logically it states tat does not give preference to anyone tuples over others. Thus we cannot have numbering of the tuples. such that tuples number 7th 9th 25th etc, no such thing exists in relation . the relation gives equal emphasis in each of its tuples.


this properties leads of another definition of relation an alternative definition of a relation can be given making the ordering of values in a tuple unnecessary.
In this definition a relation schema
Branch name
Branch city
Assets  
Downton
 Broklin
900000
Redwood
Polo
50000
Minus
Rye
400000

in case of the table , it is mandatory for the database management systems to give numbering to the records of the table. it is done to you uniquely identify each records in the database and process top down ordering among the record.

It is usually done
on the basic of the first come ,first serve. the record Store earlier in so
fast and the other follow them.


Attributes are unordered left to right  :-this property follows from the fact that the heading of relation is also a set of attributes. in case of the account relation you first right account number and then branch name, it would not make any difference. If the value of branch name is downtown and value of account number is A-101 then it does not make any difference in writing first A- 101 and then Downtown; as it still represent the same entry instance the same tuple.

Ordering of attributes it's also managed by front and tools. It is you need to to decide which attribute has to be placed and where. it is as per the requirement of the end user.

This feature ads
one more difference between relation and the table. As in case of table
specific ordering of attribute is done and is again usually on the basic of
First Come First serve from left to right in the table.


Each tuple contains exactly one value of each attributes  :- this property state that each to tuple is in atomic value. that is not divisible into components. within the frame work of the basic relationship model. hence composite and multi value attribute are not allowed. Thus relational models follows the process of normalization to overcome this problem.


Multi valued
attribute must be represented by separate relations and composite attributes
are represented by their component attribute.
What sometimes the
value of the attribute within a particular tuple. maybe unknown or may be not
applied to be tuple. A special value called NULL is used for these case. in
unknown" "value exist but not available" or "attribute does
general we can have several type of null values. "such as value
not apply to this tuple".




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