Distributed Database Management Systems: Lecture 15. The main topics covered in this chapter include: PHF- Minimality of Pr; PHF-COM-MIN algorithm; primary horizontal partitioning algorithm; derived horizontal fragmentation (DHF);...
Distributed Database Management Systems Lecture 15 PHF- Minimality of Pr Virtual University of Pakistan • A relevant predicate is the one if it influences how fragmentation is performed (fragments f into fi and fj) then there should be at least one application that accesses fi and fj differently Virtual University of Pakistan If all predicates in a set Pr are relevant then the set is minimal Virtual University of Pakistan PHF-COM-MIN Algorithm Virtual University of Pakistan • Given: a relation R and a set of simple predicates Pr • Output: a complete and minimal set of simple predicates Pr’ for Pr Virtual University of Pakistan • Rule 1: a relation or fragment is partitioned into at least two parts which are accessed differently by at least one application Virtual University of Pakistan 1-Initialization: –Find a pi ∈ Pr such that pi, partitions R according to Rule Pr’ ← pi Pr ← Pr – pi Virtual University of Pakistan 2- Iteratively add predicates to Pr' until it is complete, find a pj ∈ Pr such that pj partitions R according to Rule set Pr' = Pr' U pi ; Pr = Pr – pi ; Virtual University of Pakistan if pk in Pr' is non-relevant then Pr' = Pr' – pk Virtual University of Pakistan 10 • Implications must be based on the database semantics not on a particular extension of the database Virtual University of Pakistan 22 PROJ pNo pName budget Loc P1 Instrumentation 3.5M Lahore P2 Database Dev 2.3M Rawalpindi P3 CAD/CAM 1.9M Rawalpindi P4 Maintenance 1.6M Peshawar Virtual University of Pakistan 23 pNo pName budget Loc P1 Instrumentation 3.5M Lahore P2 Database Dev 2.3M Rawalpindi P3 CAD/CAM 1.9M Rawalpindi P4 Maintenance 1.6M Peshawar Virtual University of Pakistan 24 Derived Horizontal Fragmentation(DHF) Virtual University of Pakistan 25 • Defined on a member relation of a link according to a selection operation specified on its owner Virtual University of Pakistan 26 • Two important points: – Each link is an equi-join – Equijoin can be implemented by means of semi-joins Virtual University of Pakistan 27 • So we are interested in defining the partitions of member based on fragmentation of its owner, but want to see attributes only from member, so Virtual University of Pakistan 28 Ri = R ⋉ Si, 1≤ i ≤ w where w is the maximum number of fragments that will be defined on R and Si = Fi (S), where Fi is formula for PHF on S Virtual University of Pakistan 29 DHF Example Virtual University of Pakistan 30 PAY title, sal L1 EMP eNo, Name, titke ASIGN jNo, jName, budget, loc eNo, jNo, resp, dur Virtual University of Pakistan 31 PROJ • Considering the link L1 above: • owner (L1) = PAY member (L1) = EMP • We want to group employees on the basis of their salaries one with salary less than or equal to 30,000/- and other more than that Virtual University of Pakistan 32 eNo eName title E1 T Khan Elec Eng E2 W Shah Sys Ana E3 R Dar Mech Eng E4 K Butt Programme E5 F Sahbai Sys Ana E6 A Haq Elec Eng E7 S Farhana Mech Eng E8 M Daud Sys Ana Virtual University of Pakistan 33 Title Sal Elect Eng 40000 Sys Analyst 34000 Mech Eng 27000 Programmer 24000 Virtual University of Pakistan 34 eNo eName title E1 T Khan Elec Eng E2 W Shah Sys Ana E5 F Sahbai Sys Ana E6 A Haq Elec Eng E8 M Daud Sys Ana E3 R Dar Mech Eng E4 K Butt Programme E7 S Farhana Mech Eng Virtual University of Pakistan 35 Thanks ... be based on the database semantics not on a particular extension of the database Virtual University of Pakistan 22 PROJ pNo pName budget Loc P1 Instrumentation 3.5M Lahore P2 Database Dev 2.3M... implications among pi Pr • eliminate the contradictory minterms from M Virtual University of Pakistan 15 PHF – Example II Virtual University of Pakistan 16 Find the name and budget of projects given... Peshawar Virtual University of Pakistan 23 pNo pName budget Loc P1 Instrumentation 3.5M Lahore P2 Database Dev 2.3M Rawalpindi P3 CAD/CAM 1.9M Rawalpindi P4 Maintenance 1.6M Peshawar Virtual University