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Università degli Studi di Modena e Reggio Emilia The MOMIS project - D. Beneventano, S. Bergamaschi, F. Mandreoli Università

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Presentation on theme: "Università degli Studi di Modena e Reggio Emilia The MOMIS project - D. Beneventano, S. Bergamaschi, F. Mandreoli Università"— Presentation transcript:

1 Università degli Studi di Modena e Reggio Emilia The MOMIS project - D. Beneventano, S. Bergamaschi, F. Mandreoli Università degli Studi di Modena e Reggio Emilia MOMIS Query Manager Prototipo di un query manager per la gestione di query globali D2I Integrazione, Warehousing e Mining di sorgenti eterogenee Tema 1: Integrazione di dati provenienti da sorgenti eterogenee ROMA, 11 OTTOBRE 2002

2 Università degli Studi di Modena e Reggio Emilia The MOMIS project - Example S(G) = (Name,E_mail,Year,Dept,Section) Local classes (relational) NameE_mailSectionYearDept L1firstn and lastne_mailnullyearnull L2namee_mails_codenulldept_code S(L1) = (Name,E_mail,Year)S(L2) = (Name,E_mail,Dept,Section) Local Class Schemata w.r.t. Global Class: Global Class Schema: G L1(firstn,lastn,year,e_mail) L2(name,e_mail,dept_code,s_code) Global Class: G INTEGRATION

3 Università degli Studi di Modena e Reggio Emilia The MOMIS project - Data cleaning and reconciliation namee_maildept_cS_code firstnlastne_mailyear NameE_mailYear Rita Ada NameE_mailDeptSection Ada Ugo Schema Translation (example: firstn and lastn to Name ) Data conversion (example: Rita + Verde to Rita Verde ) L1 Integration at the extensional level the data returned by various sources need to be converted/reconciled interpretation and merging of the data provided by the sources L2

4 Università degli Studi di Modena e Reggio Emilia The MOMIS project - L1 L2 O1O O2 NameE_mailYear Rita Verde Ada O O1 O2 O NameE_mailDeptSection Ada Ugo Redundancy and Reconcilation Instances of the same object in different local class must have the same value for a common attribute Hypothesis L2 L1

5 Università degli Studi di Modena e Reggio Emilia The MOMIS project - Object fusion L1 L2 O1O O2 NameE_mailYear Rita Ada Name Ada Rossi JoinMap JM(L1,L2) L1.Name=L2.Name NameE_mailDeptSection Ada Ugo O O1 O2 O To identify instances of the same object and fuse them: JoinMap - join criteria among classes

6 Università degli Studi di Modena e Reggio Emilia The MOMIS project - Object fusion : indirect map L1 L2 O1O2 O3 IdNameE_mailYear 123Rita 243Ada MatrSN 243XY JoinMap JM CS.S,UNI.RS E_mailDeptSN O2 O1 O3 O2

7 Università degli Studi di Modena e Reggio Emilia The MOMIS project - NameE_mailYear Rita Ada NameE_mailDeptSection Ada Ugo Global Class Instance L2 NameE_mailYearDeptSection Ada Rita Ugo L1 G The computation is based on FULL DISJUNCTION (Rajarama, Ullman - Integrating Information by Outerjoins and Full Disjunctions. PODS 1996) Computing the natural outerjoin of many relations in a way that preserves all possible connections amon facts G: select S(G) from L1 outer join L2 on JM(L1,L2) GAV with Single database property (Lenzerini - Data Integration: A Theoretical Perspective, PODS 2002)

8 Università degli Studi di Modena e Reggio Emilia The MOMIS project - FULL DISJUNCTION COMPUTATION Question: when a full disjunction can be computed by some sequence of natural outerjoins Answer: there is a natural outerjoin sequence producing the full disjunction if and only if the set of relation schemes forms a connected, -acyclic hypergraph (Fagin ) A Global class with n local classes, n >2 : -cyclic hypergraph G: select S(G) from (L1 outer join L2 on JM(L1,L2)) outer join (L1 outer join L3 on JM(L1,L3)) on JM(L2,L3) Example: n = 3 : New Method L1 L2 L3 JM(L1,L3) JM(L1,L2) JM(L2,L3)

9 Università degli Studi di Modena e Reggio Emilia The MOMIS project - Query rewiting method Global query (in DNF) : Q1 Local query for the class L : Q1_L where-condition of Q1_L : all factors of DNF which can be solved in L residual factors of Q1 : factors not included in all local where-condition select-list of Q1_L : attributes of the select-list of Q1 + residual factors +JoinMap Global query reformulation full disjunction based on the JoinMap + residual factors

10 Università degli Studi di Modena e Reggio Emilia The MOMIS project - Query rewiting example Q1: select E_mail from G where (E_mail like *.it' and Dept='Dept1') or (E_mail like *.it' and Year=2) Q1_L1: select Name, Year, E_mail from L1 where (E_mail like *.it' or Year=2) Q1_L2: select Name, Dept, E_mail from L2 where (E_mail like *.it' or Dept='Dept1') Q1: select E_mail from Q1_L1 outer join Q1_L2 on JM where (Dept='Dept1' or Year=2) residual factor Global query Local queries Global query reformulation:


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