"if" in SPARQL query
my problem is very simple: I have a source my:g1
that contains:
my:a1 my:b "literal 1"
Then I have a second source my:g2
that contains:
my:a2 my:b my:c.
my:c rdfs:label "literal 2"
how can I set up a SPARQL query that creates something like:
| ?a | ?b | ?literal |
|-------|-------|-------------|
| my:a1 | my:b | "literal 1" |
| my:a2 | my:b | "literal 2" |
i.e. how can I tell sparql to use the same variable for "literal 1"
and "literal 2"
: I am looking for something like
Select ?a ?b ?literal
where {
if (?g = my:g1) then
GRAPH ?g { ?a ?b ?literal}
else if (?g = my:g2) then
GRAPH ?g { ?a ?b ?c. ?c rdfs:label ?literal}
}
NOTE. I know this request is terribly wrong, but just to clarify my intent.
EDIT:
in this particular case the "union" operator, for example
select ?a ?b ?literal
where {
{
GRAPH my:g1 { ?a ?b ?literal}
}
union
{
GRAPH my:g2 { ?a ?b ?c. ?c rdfs:label ?literal}
}
}
will work, but this is not my "real" case. Are there any other solutions?
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You can use property path and filter. The trick here is that a property path with a question mark means a path of length 0 or 1. If the path has length 0, then? Literal is the same as? C, which covers the case where α a is related directly to literal. If the path has length 1, then? Literal is rdfs: label meaning for? C.
Here's an example with real data:
@prefix : <urn:ex:>
:a :b "literal 1" .
:a :b :c .
:c :label "literal 2" .prefix : <urn:ex:>
select distinct ?a ?b ?literal where {
?a ?b ?c .
?c :label? ?literal
filter isLiteral(?literal)
}
----------------------------- | a | b | literal | ============================= | :a | :b | "literal 1" | | :a | :b | "literal 2" | | :c | :label | "literal 2" | -----------------------------
You might not have expected the last line in the results, but what if? a and? b are variables, then it makes sense because it says nothing about what a variable is ? b must be associated with a specific property : b .
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