Vertical Fragmentation-Vertical fragmentation groups together only those attributes in a relation that are used jointly by various important transactions. A vertical fragment is described using the Projection operation of the relational algebra. In its most easy form, vertical fragmentation is the similar as that of decomposition. In common, a relation can be constructed on taking Natural join of all vertical fragments.

More usually, vertical fragmentation is accomplished by adding a special attribute known as a tuple-number to the scheme R. A tuple-number is a logical or physical address for a tuple. Therefore every tuple in R must have a unique address, the tuple- number attribute is a key to the new fragments get (please refer to Figure ).

Branch-code	Account number	Customer name	Balance	Tuple-number
1101	3050	Suresh	5000	1
1101	2260	Swami	3360	2
1102	1170	Swami	2050	3
1102	4020	Khan	10000	4
1101	1550	Khan	620	5
1102	4080	Khan	1123	6
1102	6390	Khan	7500	7

                                      Figure: The relation DEPOSIT of figure 5 with tuple- numbers

This  relation  now  can  be  decayed  into  two  fragments  as:  demonstrates  a  vertical decomposition of the scheme Deposit-scheme tuple number into:

DEPOSIT3 = ∏  (branch-code. customer-name, tuple-number) (DEPOSIT)

DEPOSIT4 = ∏  (account-number, balance, tuple-number) (DEPOSIT)

The example of above Figure on this basis would become:

DEPOSIT3
Branch-code	Customer-name	Tuple-number
1101	Suresh	1
1101	Swami	2
1102	Swami	3
1102	Khan	4
1101	Khan	5
1102	Khan	6
1102	Khan	7
DEPOSIT4
Account number	Balance	Tuple-number
3050	5000	1
2260	3360	2
1170	2050	3
4020	10000	4
1550	620	5
4080	1123	6
6390	7500	7

                                                     Figure: Vertical fragmentation of relation DEPOSIT

How can we rebuild the original relation from these 2 fragments? By taking natural join of the 2 vertical fragments on tuple-number. The tuple number permits direct retrieval of the tuples without the required for an index. Therefore, this natural join may be computed much extra efficiently than typical natural join.Though, please note that as the tuple numbers are system generated, thus they should not be visible to common users. If users are given access to tuple-number, it happens to impossible for the system to change tuple addresses.

 

Posted Date: 3/13/2013 8:41:23 AM | Location : United States

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