Database Reference
In-Depth Information
Algorithm 1 translates a mapping into an appropriate XQuery program. By
x
,
y
,
v
(possibly with
subscripts) we denote variables, while $
x
, $
y
, $
v
are the corresponding XQuery variables.
Algorithm 1.
(
translating a mapping m
ST
to XQuery program
)
Input
: A mapping
∧
x
(
S
(
x
)
∧
∧
y
T
(
x'
,
y
)), where:
S
:= /
if
[
E'
],
T
:= /
l
[
E
],
y
= (
y
1
, ...,
y
m
).
Output
: Query in XQuery over
S
transforming an instance of
S
into the corre-
sponding
canonical instance of
T
.
mappingToXQuery
(
∧
x
(/
if
[
E'
]
∧
∧
y
1
, ...,
y
m
/
l
[
E
]) =
<
l
>{
let
$
y
1
: = “
null
”, ..., $
y
m
:= “
null
”
for
$
v
in
doc(“...”)/
if
,
τ($
v
,
E'
)
return
ρ(
E
)}
</
l
>
where:
1. τ($
v
,
l = x
) = $
x
in if
($
v
[
l
])
then
$
v
/
l
/
text()
else
“
null
”,
2. τ($
v
,
l
[
E
]) = $
v'
in if
($
v
[
l
])
then
$
v
/
l
else
/, τ($
v'
,
E
),
3. τ($
v
,
E
1
, ...,
E
k
) = τ($
v
,
E
1
), ..., τ($
v
,
E
k
),
and
4. ρ(
l = x
) = <
l
>{$
x
}</
l
>
5. ρ(
l
[
E
]) = <
l
>ρ(
E
)</
l
>
6. ρ(
E
1
, ...,
E
k
) = ρ(
E
1
) ... ρ(
E
k
)
For the mapping from Example 4, Algorithm 1 generates the following XQuery program:
Query 1:
<pubs>{
let $x4:=”null”
for $_v in doc(“I3.xml”)/authors,
$_v1 in if ($_v[author]) then $_v/author else /,
$x1 in if ($_v1[name]) then $_v1/name/text() else “null”,
$_v2 in if ($_v1[paper]) then $_v1/paper else /,
$x2 in if ($_v2[title]) then $_v2/title/text() else “null”,
$x3 in if ($_v2[year]) then $_v2/year/text() else “null”
return
<pub>
<title>{$x2}</title>
