Distributed Database Management Systems: Lecture 13. The main topics covered in this chapter include: interests of the local and head offices mar result following vertical partitions of this table: EMP1(eId, eName, eDept); EMP2(eId, eQual, eSal); degree of fragmentation; correctness rules for fragmentation;...
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Lecture 13
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How
Interests of the local and head offices mar result following vertical
partitions of this table:
EMP1(eId, eName, eDept) EMP2(eId, eQual, eSal)
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1- Vertical; Different subsets of
attributes are stored at different
places, like,
Table EMP(eId, eName, eDept, eQual, eSal)
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Interests of the local and head offices may result following vertical partitions of this
table:
EMP1(eId, eName, eDept)
EMP2(eId, eQual, eSal)
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CLIENT
(cAC#, cName, cAdr, cBal) table is
placed in different databases based on their location, like from Lahore, Pindi, Karachi, Peshawar, Quetta
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3- Degree of Fragmentation
Between no to the extreme level that could be to the individual tuple or
column level; a compromised decision
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4- Correctness Rules for
Fragmentation
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• Completeness: each of the data item
(a tuple or a attribute) that can be in R can also be in one or more Ri
∀
∀ x R, Rx R, R∈∈ ∃∃ i such that x R such that x R∈∈ i
Resembles Lossless decomposition
property in Normalization
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• Reconstruction: it should be
possible to define a relational operator such that the original relation can be reconstructed
R = g(R1, R2, …, Rn)
Reconstruction ensures that the dependencies of the original
relation are preserved in
fragmentation
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• Disjoint ness:
if data item x is in Rj, it is not in any other fragment
∀
∀ x Rx R∈∈ i, R R∃∃ j such that x R such that x R∈∈ j, i ≠ j
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• Allocation Strategy:
Partitioned, fully or partially replicated; depends mainly on requirements
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Horizontal Fragmentation
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• is performed based on some
Predicate/ Condition
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Primary Horizontal Fragmentation(PHF)
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Information Requirements
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Database Information: We may
need to consult the conceptual
DB design
RDM being Semantically not that rich
Apart from tables, we need
relationships, cardinality and the owner and member tables
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owner = PAY member = EMP title, sal
eNo, jNo, resp, dur
PAY
EMP
ASIGN
PROJ
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Application Requirement