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

2. Example Local classes (relational) L1(firstn,lastn,year,e_mail)
L2(name,e_mail,dept_code,s_code)
INTEGRATION
Global Class: G
Name
E_mail
Section
Year
Dept L1
firstn and lastn
e_mail
null
year L2
name
s_code
dept_code
Global Class Schema: G
S(G) = (Name,E_mail,Year,Dept,Section)
Local Class Schemata w.r.t. Global Class:
S(L1) = (Name,E_mail,Year) S(L2) = (Name,E_mail,Dept,Section)

3. Data cleaning and reconciliation
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
Schema Translation
(example: firstn and lastn to Name)
Data conversion
(example: ‘Rita’ + ‘Verde’ to ‘Rita Verde’)
firstn
lastn
e_mail
year
Rita
Verde 2
Ada
Rossi 1
name
e_mail
dept_c
S_code
Rossi_Ada
Dept1
413245
Po_Ugo
2314 L1 L2
Name
E_mail
Year
Rita Verde 2
Ada Rossi 1
Name
E_mail
Dept
Section
Ada Rossi
Dept1
413245
Ugo Po
2314

4. Redundancy and Reconcilation
Hypothesis
Instances of the same object in different local class must have
the same value for a common attribute L2 L1 O1 O O2 L1 L2
Name
E_mail
Year
Rita Verde 2
Ada Rossi 1
Name
E_mail
Dept
Section
Ada Rossi
Dept1
413245
Ugo Po
2314 O1 O O O2

5. Object fusion
To identify instances of the same object and fuse them: JoinMap - join criteria among classes L1 L2 O1 O O2
Name
E_mail
Year
Rita Verde 2
Ada Rossi 1
Name
E_mail
Dept
Section
Ada Rossi
Dept1
413245
Ugo Po
2314 O1 O O O2
JoinMap JM(L1,L2)
L1.Name=L2.Name
Name
Ada Rossi

6. Object fusion : indirect mapL1 L2 O1 O2 O3 Id
Name
E_mail
Year
123
Rita Verde 2
243
Ada Rossi 1
E_mail
Dept SN
Dept1
XY413245
XZ2314 O1 O2 O2 O3
JoinMap
JMCS.S,UNI.RS
Matr SN
243
XY413245

7. Global Class Instance G GAV with “Single database property”
(Lenzerini - Data Integration: A Theoretical Perspective, PODS 2002)
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” L1
Name
E_mail
Year
Rita Verde 2
Ada Rossi 1 L2
Name
E_mail
Dept
Section
Ada Rossi
Dept1
413245
Ugo Po
2314
G: select S(G) from L1 outer join L2 on JM(L1,L2) G
Name
E_mail
Year
Dept
Section
Ada Rossi 1
Dept1
413245
Rita Verde 2
Ugo Po
2314

8. 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 L1
JM(L1,L2)
JM(L1,L3)
New Method
JM(L2,L3) L2 L3
Example: n = 3 :
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)

9. 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. Query rewiting example
Global query
Q1: select E_mail
from G
where (E_mail like ’*.it' and Dept='Dept1') or (E_mail like ’*.it' and Year=2)
Local queries
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')
Global query reformulation:
Q1: select E_mail from Q1_L1 outer join Q1_L2 on JM
where (Dept='Dept1' or Year=2)
residual factor