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 ).
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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:
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DEPOSIT3
|
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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.