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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
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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 null
L2 name e_mail s_code null 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)
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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)

name e_mail dept_c S_code
Rossi_Ada RA_at_i.it Dept1 413245
Po_Ugo UP_at_i.it Dept1 2314
firstn lastn e_mail year
Rita Verde PV_at_i.it 2
Ada Rossi RA_at_i.it 1
L1
L2
Name E_mail Year
Rita Verde PV_at_i.it 2
Ada Rossi RA_at_i.it 1
Name E_mail Dept Section
Ada Rossi RA_at_i.it Dept1 413245
Ugo Po UP_at_i.it Dept1 2314
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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
L2
L1
Name E_mail Year
Rita Verde PV_at_i.it 2
Ada Rossi RA_at_i.it 1
Name E_mail Dept Section
Ada Rossi RA_at_i.it Dept1 413245
Ugo Po UP_at_i.it Dept1 2314
O1
O
O
O2
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Object fusion
To identify instances of the same object and fuse
them JoinMap - join criteria among classes
L2
L1
O1
O
O2
Name E_mail Year
Rita Verde PV_at_i.it 2
Ada Rossi RA_at_i.it 1
Name E_mail Dept Section
Ada Rossi RA_at_i.it Dept1 413245
Ugo Po UP_at_i.it Dept1 2314
O1
O
O
O2
JoinMap JM(L1,L2) L1.NameL2.Name
Name Name
Ada Rossi Ada Rossi
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Object fusion indirect map
L1
L2
O1
O2
O3
Id Name E_mail Year
123 Rita Verde PV_at_i.it 2
243 Ada Rossi RA_at_i.it 1
E_mail Dept SN
RA_at_i.it Dept1 XY413245
UP_at_i.it Dept1 XZ2314
O1
O2
O2
O3
JoinMap JMCS.S,UNI.RS
Matr SN
243 XY413245
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Global Class Instance

• 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 PV_at_i.it 2
Ada Rossi RA_at_i.it 1
L2
Name E_mail Dept Section
Ada Rossi RA_at_i.it Dept1 413245
Ugo Po UP_at_i.it Dept1 2314
G select S(G) from L1 outer join L2 on JM(L1,L2)
G
Name E_mail Year Dept Section
Ada Rossi RA_at_i.it 1 Dept1 413245
Rita Verde PV_at_i.it 2
Ugo Po UP_at_i.it Dept1 2314
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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 - 1983)

A Global class with n local classes, n gt2
?-cyclic hypergraph
L1
JM(L1,L3)
JM(L1,L2)
New Method
JM(L2,L3)
L3
L2
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)
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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
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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 Year2)
Local queries
Q1_L1 select Name, Year, E_mail from L1
where (E_mail like .it' or Year2)
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 Year2)
residual factor