Algorithm 2 Compute Mapping
INPUT: ρs OUTPUT: Π
1: 2: 3: 4: 5: 6: 7: 8: 9: 10:	πs = [] for i =1..|ρs| − 1 do  <f, v> ← ρs[i]  <f’, v′> ← ρs[i + 1]  l ← DB[s].query(“l” | δlf == 1 & δlf’ == 1)  n ← DB[s].query(“n” | δvn == 1)  n′ ← DB[s].query(“n” | δv′n == 1)  e ← DB.query(“e” | δne == 1 & δn′e == 1)  πs.add(<l,e>) return Π