Distributed Database Management Systems: Lecture 17

Distributed Database Management Systems: Lecture 17. The main topics covered in this chapter include: continue with VF to information requirement; attribute affinities; replication of Key attributes does not violate the disjoint ness condition;...

Distributed Database Management Systems Lecture 17 In this Lecture • Continue with VF – Information Requirement – Attribute affinities Virtual University of Pakistan Replication of Key attributes does not violate the disjoint ness condition Virtual University of Pakistan Vertical Fragmentation Information Requirements Virtual University of Pakistan • Basic idea of VF is access efficiency • Information Requirement is application based • Attribute affinities: obtained from more primitive usage data Virtual University of Pakistan • (80-20 Rule) • Attribute usage values: Given a set of queries Q = {q1 , q2 ,…, qq} that will run on the relation R[A1, A2 ,…, An] Virtual University of Pakistan Attribute Usage Value use(qi,Aj ) use(qi,Aj ) = 1 if attribute Aj is      referenced by query qi 0 otherwise use(qi,• ) can be defined accordingly Virtual University of Pakistan PROJ(jNo, jName, budget, loc) q1: SELECT BUDGET FROM PROJ WHERE JNO=Value q2: SELEC JNAME, BUDGET FROM PROJ Virtual University of Pakistan q3: SELECT JNAME FROM PROJ WHERELOC=Value q4: SELECTSUM(BUDGET) FROM PROJ WHERE LOC=Value Let A1= jNo, A2= jName, A3= budget, A4= loc Virtual University of Pakistan q1 q2 q3 q4 A1   A2 A3 A4 0 0 1 1       1    0       1            1 Attribute Usage Matrix Virtual University of Pakistan 10 • AUM does not represent the query frequency at different sites; • Attribute affinity between two attribute A i and Aj, affinity (Ai, Aj), of a relation R(A1, A2, …., An) with respect to applications set Q = {q1, q2, …, qq) is Virtual University of Pakistan 11 aff(Ai, Aj) = ∑ k|use(qk, Ai) = ∑ refl(qk)accl(qk) use(qk, Aj) = 1∀ sites where refl(qk) is number of accesses to attributes (Ai, Aj) for each execution of qk at site Sl, and… accl(qk) is application access frequency measure from Sl Virtual University of Pakistan 12 Attribute Usage Matrix A A A A S1 S2 S3 q1 1 q1 15 20 10 q2 1 q2 0 q3 1 q3 25 25 25 q4 0 1 q4 0 Virtual University of Pakistan Access Frequency Matrix 13 acc1(q1) = 15, acc2(q1) = 20,  acc3(q1) = 10 acc1(q2) = 5,   acc2(q2) = 0,    acc3(q2) = 0 acc1(q3) = 25, acc2(q3) = 25,   acc3(q3) = 25 acc1(q4) = 3,   acc2(q4) = 0,     acc3(q4) = 0 Virtual University of Pakistan 14 aff(A3, A4)  = ∑k = 4 ∑l =1 3 refl(qk)accl(qk)  = 3 *1 + 0 + 0 = 3 aff(A1, A2) = 0,  Since no qi accesses them both aff(A2, A2) =  5 * 1 + 0  + 0  = 5 25 * 1 + 25 *1 + 25 * 1 = 75 + 5 = 80 Virtual University of Pakistan 15 S1 S2 S3 q1 15 20 10 q2 0 q3 25 25 25 1 q4 0 A1 A2 A3 A4 q1 1 q2 1 q3 q4 0 Virtual University of Pakistan 16 Attribute affinity matrix (AA)  A1 A2 A3 A4 A1 45 45 A2 80 75 A3 45 53 A4 75 78 Virtual University of Pakistan 17 Clustering Algorithm • VF is based on identifying groups of attributes based on AA • Vertical Clustering is based on Bond Energy Algorithm (BEA); it uses AA; identifies groups of similar items Virtual University of Pakistan 19 • Large affinity attributes are combined together and lower together • BEA takes as input the AA and generates the cluster affinity matrix CA Virtual University of Pakistan 20 Global Affinity Measure (AM) • Affinity Measure is a single value that is calculated on the basis of positions of elements in AA and their surrounding elements Virtual University of Pakistan 22 A1 A2 A3 A4 A1 45 45 A2 80 75 A3 45 53 A4 75 78 Virtual University of Pakistan 23 n n ∑ ∑ aff(Ai, Aj) [aff(Ai, Aj­1) + aff(Ai, Aj+1)                + aff(Ai­1, Aj) + aff(Ai+1, Aj) ] AM =  i = 1 j = 1 aff(A0, Aj)= aff(Ai, A0)= aff(An+1, Aj)= aff(Ai, An+1)=0 Virtual University of Pakistan 24 A1 A2 A3 A4 A1 45 45 A2 80 75 A3 45 53 A4 75 78 Virtual University of Pakistan 25 ...In this Lecture • Continue with VF – Information Requirement – Attribute affinities Virtual University of... Attribute affinity matrix (AA)  A1 A2 A3 A4 A1 45 45 A2 80 75 A3 45 53 A4 75 78 Virtual University of Pakistan 17 Clustering Algorithm • VF is based on identifying groups of attributes based on AA • Vertical