Database Reference
In-Depth Information
M
,
Q
)
Algorithm 15.6 I
NL
C
ERT
A
NSW
(
Require:
S
is a source document.
Ensure: The returned set of tuples is
certain
M
(
Q
,
S
).
S
r
:= I
NL
D
OC
(
S
,
D
s
)
M
r
:= I
NL
M
AP
(
)
Q
r
:= I
NL
Q
UERY
(
Q
,
D
t
)
Compute the canonical universal solution
T
r
for
S
r
under
M
M
r
.
Compute
Q
r
(
T
r
);
Discard tuples with nulls from
Q
r
(
T
r
);
return
Q
r
(
T
r
);
mapping
M
query
Q
certain
M
(
Q
,
S
)
source
S
univ. sol.
T
I
NL
D
OC
(
S
,
D
s
)
I
NL
D
OC
(
T
,
D
t
)
M
r
= I
NL
M
AP
(
M
)
Q
r
= I
NL
Q
UERY
(
Q
,
D
t
)
certain
M
r
(
Q
r
,
T
r
)
S
r
T
r
Figure 15.4 XML data exchange via relations: solution
in SM
nr
(
Example 15.13 We now specify a complete XML schema mapping
,
=).
As the source DTD
D
s
,wetaketheDTD
D
used in all other examples in the chapter, and
as the source source tree
S
we take the tree in
Figure 15.2
.ThetargetDTD
D
t
has two
productions
M
↓
r
→
writer
∗
writer
:@
name
writer
→
work
∗
work
:@
title
,
@
year
.
Suppose we have a single dependency in
Σ
st
:
r
/
book
(
x
)
/
author
/
name
(
y
)
→∃
z
r
/
writer
(
y
)
/
work
(
x
,
z
)
,
restructuring book-author pairs into writer-works pairs, with a null
z
introduced for
the unknown attribute
@year
. We denote
r
/
book
(
x
)
/
author
/
name
(
y
) by
(
x
,
y
) and
π
r
/
writer
(
y
)
/
work
(
x
,
z
) by
π
(
x
,
y
,
z
).
The inlining schema I
NL
S
CHEMA
(
D
t
) is given by
R
r
(
rID
)
R
writer
(
writerID,rID,@name
)
R
work
(
workID,writerID,@title,@year
)
with keys underlined, as well as two foreign keys:
R
writer
(
rID
)
⊆
FK
R
r
(
rID
) and
R
work
(
writerID
)
⊆
FK
R
writer
(
writerID
).
