1. Distributed Database Management Systems
Lecture 14

2. Virtual University of Pakistan
DHF
The inputs required for DHF
The set of partitions for owner
Member relation
Semi-join predicates between owner and member
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3. Virtual University of Pakistan
DHA
Care in case of multiple owners, like ASIGN
Fragmentation selection depends:
1- One with better Join Characteristics
2- One used in more applications
Second one is straight forward, we should try to facilitate heavy users; the first one needs more considerations
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4. Virtual University of Pakistan
DHF
For the first point;
Join is performed on smaller relations, that increases efficiency
The join can be performed in parallel in case of simple graphs, that improves efficiency as well; simple graph means
PAY1
PAY2
EMP1
EMP2
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5. Virtual University of Pakistan
DHF
demonstrates two things
1-Derived fragmentation may follow a chain, like
PAY-EMP-ASIGN
2-Typically, more than one fragmentation options are there, which one adopted is an allocation problem discussed later
Checking for Correctness
Completeness: for PHF depends on Pr’, and in DHF, completeness of owner Pr’, and the referential integrity constraint
Reconstruction: Involves Union in both cases
Disjointness: Simple in PHF if the pi in Pr’ are mutually exclusive; in DHF, guaranteed in case of simple join graph, however in case of partitioned join graph it is hard to establish
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6. Checking for Correctness
Completeness: for PHF depends on Pr’, and in DHF, completeness of owner Pr’, and the referential integrity constraint
Let R be member S be owner
Fs = { S1,S2,…Sn}
‘A’ the common attribute
t[A] = t’ [A]
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Reconstruction:
Involves Union in both cases
FR = {R1,R2,….Rn}
R = U Ri ∀ Ri ∈FR
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Disjoint ness:
Simple in PHF if the pi in Pr’ are mutually exclusive; in DHF, guaranteed in case of simple join graph, however in case of partitioned join graph it is hard to establish
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9. Vertical Fragmentation (VF)
Vertical subset of relation
A VF of a relation produces fragments R1, R2, …. Rn, each of which contains subset of attributes of R and PK of R.
Objective is to produce smaller relations, so that most of the applications run on smaller relations; so they become fast.
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10. Virtual University of Pakistan
Vertical Fragment
Vertical fragmentation is more complicated, since more alternatives exist.
VF is mainly based on heuristics
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11. Virtual University of Pakistan
Example of VF
CUST
A/C#
Name
Bal
Branch
AB101
Saeed
4535
MTN
AB202
Laeeq
LHR
AB203
Salma
AB109
Shaan
45.32
Delta = ΠA/C#, Name, Branch (CUST)
Beta = ΠA/C#, Bal (CUST)
Delta
Beta
A/C#
Name
Branch
AB101
Saeed
MTN
AB202
Laeeq
LHR
AB203
Salma
AB109
Shaan
A/C#
Bal
AB101
4535
AB202
AB203
AB109
45.32
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12. Virtual University of Pakistan
Two Alternatives of VF
Grouping: Starting with single attribute VFs and then combining different attributes
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13. Virtual University of Pakistan
Two Alternatives of VF
Splitting: Starting from the whole relation and then breaking it down analyzing the nature of applications
Later suits better to DDB environment; results non-overlapping fragments; so discussed here
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14. Thanks