[topbraid-users] Problem with IF in SPARQL
I was testing a simple conditional in SPARQL and it wasn't working. So I
went to the documentation and wrote the test conditional and it worked, but
do not understand why mine isn't working. The test conditional compares 2
integers and displays 2 strings. I augmented that test to have another
nested IF and it still works.
My query is based on a BIND of 2 expressions to strings. Here is what it
looks like:
SELECT ?res
WHERE {
BIND (foo AS ?f) .
BIND (bar AS ?b) .
BIND ((IF(?f, ?f, IF(?b, ?b, NA))) AS ?res) .
}
This returns foo. If I remove the first BIND statement there is no
result. I tried changing this test to:
SELECT ?res
WHERE {
BIND (foo AS ?f) .
BIND (bar AS ?b) .
BIND ((IF(fn:string-length(?f) 0, ?f, IF(fn:string-length(?b) 0,
?b, NA))) AS ?res) .
}
and it returns foo. If I change the first size to 3, then it returns
bar. If I change the second size to 3 it returns NA.
But in 'my' query this doesn't work. Here is the query:
SELECT DISTINCT *
WHERE {
BIND
(act:commonSubclassLabel(http://developer.runkeeper.com/healthgraph#Spinning;)
AS ?res1) .
BIND
(act:commonSuperclassLabel(http://developer.runkeeper.com/healthgraph#Spinning;)
AS ?res2) .
BIND ((IF(fn:string-length(?res2) 0,
?res2, IF(fn:string-length(?res1) 0, ?res1, NA))) AS ?res) .
}
The function calls to 'commonSubclassLabel' and 'commonSuperclassLabel
work fine on their own (both return strings), and the result returned is
?res2 if its length exceeds 0. If not, there is a value for ?res1 but it
doesn't ever get bound to ?res. If I swap ?res2 and ?res1 in the last BIND
the same query works for ?res1 but not ?res2, so there is something in my
IF statements 'THEN' block that doesn't work. If I replace the THEN block
with just ?res1 (or ?res2 as the case may be), nothing changes in the
result.
As you can see, I have worked myself into a lather over this by making it
more complex than it should have to be, but as is normal in such cases when
the simple logic didn't work I began more and more convoluted things.
Any pointers would be greatly appreciated!
These queries are being executed in TBCME v4.2.
Jack
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Re: [topbraid-users] Problem with IF in SPARQL
Another thing to keep in mind is that IF will return nothing if the
condition is returning unbound (fail). For example,
IF(strlen(?a) 0, 1, 2)
will return nothing if ?a is not a string - it will fail and return
unbound - not 2. A safer way of expressing this would be
IF(bound(?a) strlen(?a) 0, 1, 2)
For some use cases, the COALESCE keyword is a better option than IF.
Not sure if this is on topic for your specific scenario.
Holger
On 2/10/2015 6:16, Jack Hodges wrote:
I was testing a simple conditional in SPARQL and it wasn't working. So
I went to the documentation and wrote the test conditional and it
worked, but do not understand why mine isn't working. The test
conditional compares 2 integers and displays 2 strings. I augmented
that test to have another nested IF and it still works.
My query is based on a BIND of 2 expressions to strings. Here is what
it looks like:
SELECT ?res
WHERE {
BIND (foo AS ?f) .
BIND (bar AS ?b) .
BIND ((IF(?f, ?f, IF(?b, ?b, NA))) AS ?res) .
}
This returns foo. If I remove the first BIND statement there is no
result. I tried changing this test to:
SELECT ?res
WHERE {
BIND (foo AS ?f) .
BIND (bar AS ?b) .
BIND ((IF(fn:string-length(?f) 0, ?f, IF(fn:string-length(?b)
0, ?b, NA))) AS ?res) .
}
and it returns foo. If I change the first size to 3, then it returns
bar. If I change the second size to 3 it returns NA.
But in 'my' query this doesn't work. Here is the query:
SELECT DISTINCT *
WHERE {
BIND
(act:commonSubclassLabel(http://developer.runkeeper.com/healthgraph#Spinning;)
AS ?res1) .
BIND
(act:commonSuperclassLabel(http://developer.runkeeper.com/healthgraph#Spinning;)
AS ?res2) .
BIND ((IF(fn:string-length(?res2) 0,
?res2, IF(fn:string-length(?res1) 0, ?res1, NA))) AS ?res) .
}
The function calls to 'commonSubclassLabel' and
'commonSuperclassLabel work fine on their own (both return strings),
and the result returned is ?res2 if its length exceeds 0. If not,
there is a value for ?res1 but it doesn't ever get bound to ?res. If I
swap ?res2 and ?res1 in the last BIND the same query works for ?res1
but not ?res2, so there is something in my IF statements 'THEN' block
that doesn't work. If I replace the THEN block with just ?res1 (or
?res2 as the case may be), nothing changes in the result.
As you can see, I have worked myself into a lather over this by making
it more complex than it should have to be, but as is normal in such
cases when the simple logic didn't work I began more and more
convoluted things.
Any pointers would be greatly appreciated!
These queries are being executed in TBCME v4.2.
Jack
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Re: [topbraid-users] Problem with IF in SPARQL
Holger and Scott,
Thank you very much for looking at this. Scott, I tried the scoping (as per
your suggestion) and it didn't change anything. I must admit that I had not
thought to run the query debugger, but I do not really understand how it
works anyway.
Holger, I tried using bound(?res2) and it worked! Thank you for pointing
this out. Incidentally, I had already tried COALESCE and it didn't work for
me (but that was several cycles ago so the logic I was working with was
perhaps different then too).
Thanks again, both of you!!!
Jack
On Mon, Feb 9, 2015 at 3:44 PM, Holger Knublauch hol...@topquadrant.com
wrote:
Another thing to keep in mind is that IF will return nothing if the
condition is returning unbound (fail). For example,
IF(strlen(?a) 0, 1, 2)
will return nothing if ?a is not a string - it will fail and return
unbound - not 2. A safer way of expressing this would be
IF(bound(?a) strlen(?a) 0, 1, 2)
For some use cases, the COALESCE keyword is a better option than IF.
Not sure if this is on topic for your specific scenario.
Holger
On 2/10/2015 6:16, Jack Hodges wrote:
I was testing a simple conditional in SPARQL and it wasn't working. So I
went to the documentation and wrote the test conditional and it worked, but
do not understand why mine isn't working. The test conditional compares 2
integers and displays 2 strings. I augmented that test to have another
nested IF and it still works.
My query is based on a BIND of 2 expressions to strings. Here is what it
looks like:
SELECT ?res
WHERE {
BIND (foo AS ?f) .
BIND (bar AS ?b) .
BIND ((IF(?f, ?f, IF(?b, ?b, NA))) AS ?res) .
}
This returns foo. If I remove the first BIND statement there is no
result. I tried changing this test to:
SELECT ?res
WHERE {
BIND (foo AS ?f) .
BIND (bar AS ?b) .
BIND ((IF(fn:string-length(?f) 0, ?f, IF(fn:string-length(?b) 0,
?b, NA))) AS ?res) .
}
and it returns foo. If I change the first size to 3, then it returns
bar. If I change the second size to 3 it returns NA.
But in 'my' query this doesn't work. Here is the query:
SELECT DISTINCT *
WHERE {
BIND (act:commonSubclassLabel(
http://developer.runkeeper.com/healthgraph#Spinning;
http://developer.runkeeper.com/healthgraph#Spinning) AS ?res1) .
BIND (act:commonSuperclassLabel(
http://developer.runkeeper.com/healthgraph#Spinning;
http://developer.runkeeper.com/healthgraph#Spinning) AS ?res2) .
BIND ((IF(fn:string-length(?res2) 0,
?res2, IF(fn:string-length(?res1) 0, ?res1, NA))) AS ?res) .
}
The function calls to 'commonSubclassLabel' and 'commonSuperclassLabel
work fine on their own (both return strings), and the result returned is
?res2 if its length exceeds 0. If not, there is a value for ?res1 but it
doesn't ever get bound to ?res. If I swap ?res2 and ?res1 in the last BIND
the same query works for ?res1 but not ?res2, so there is something in my
IF statements 'THEN' block that doesn't work. If I replace the THEN block
with just ?res1 (or ?res2 as the case may be), nothing changes in the
result.
As you can see, I have worked myself into a lather over this by making
it more complex than it should have to be, but as is normal in such cases
when the simple logic didn't work I began more and more convoluted things.
Any pointers would be greatly appreciated!
These queries are being executed in TBCME v4.2.
Jack
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TopBraid Suite Users, the topics of which include Enterprise Vocabulary
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Live, TopBraid Insight, SPARQLMotion, SPARQL Web Pages and SPIN.
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Re: [topbraid-users] Problem with IF in SPARQL
Jack; The problem may be that SPARQL's declarative nature does not
impose any ordering on its statements. One should be able to place
the statements in any order and the result will be the same.
In your case, you need to make sure the ?res1 and ?res2 binding are
performed before the IF statement, so you can include this in a
graph statement. The SPARQL engine will execute the graphs
inside-out. (If you're interested in the actual ordering of the
clauses, and don't mind a bit of Lisp-like syntax, then you can take
a look at the query in the "Debug query". This will at least let
you know whether or not an ordering is being sent to the SPARQL
engine.)
So, the following ought to do what you need by specifying that the
first two statements are executed before the rest.
SELECT DISTINCT *
WHERE {
{ BIND
(act:commonSubclassLabel("http://developer.runkeeper.com/healthgraph#Spinning")
AS ?res1) .
BIND
(act:commonSuperclassLabel("http://developer.runkeeper.com/healthgraph#Spinning")
AS ?res2) .
}
BIND ((IF(fn:string-length(?res2) 0,
?res2, IF(fn:string-length(?res1) 0, ?res1, "NA"))) AS
?res) .
}
-- Scott
On 2/9/2015 2:16 PM, Jack Hodges wrote:
I was testing a simple conditional in SPARQL and it
wasn't working. So I went to the documentation and wrote the
test conditional and it worked, but do not understand why mine
isn't working. The test conditional compares 2 integers and
displays 2 strings. I augmented that test to have another nested
IF and it still works.
My query is based on a BIND of 2 expressions to strings.
Here is what it looks like:
SELECT ?res
WHERE {
BIND ("foo" AS ?f) .
BIND ("bar" AS ?b) .
BIND ((IF(?f, ?f, IF(?b, ?b, "NA"))) AS ?res) .
}
This returns "foo". If I remove the first BIND statement
there is no result. I tried changing this test to:
SELECT ?res
WHERE {
BIND ("foo" AS ?f) .
BIND ("bar" AS ?b) .
BIND ((IF(fn:string-length(?f) 0, ?f,
IF(fn:string-length(?b) 0, ?b, "NA"))) AS ?res) .
}
and it returns "foo". If I change the first size to 3, then
it returns "bar". If I change the second size to 3 it returns
"NA".
But in 'my' query this doesn't work. Here is the query:
SELECT DISTINCT *
WHERE {
BIND
(act:commonSubclassLabel("http://developer.runkeeper.com/healthgraph#Spinning")
AS ?res1) .
BIND
(act:commonSuperclassLabel("http://developer.runkeeper.com/healthgraph#Spinning")
AS ?res2) .
BIND ((IF(fn:string-length(?res2) 0,
?res2, IF(fn:string-length(?res1) 0, ?res1, "NA"))) AS
?res) .
}
The function calls to 'commonSubclassLabel' and
'commonSuperclassLabel" work fine on their own (both return
strings), and the result returned is ?res2 if its length
exceeds 0. If not, there is a value for ?res1 but it doesn't
ever get bound to ?res. If I swap ?res2 and ?res1 in the last
BIND the same query works for ?res1 but not ?res2, so there is
something in my IF statements 'THEN' block that doesn't work.
If I replace the THEN block with just ?res1 (or ?res2 as the
case may be), nothing changes in the result.
As you can see, I have worked myself into a lather over
this by making it more complex than it should have to be, but
as is normal in such cases when the simple logic didn't work I
began more and more convoluted things.
Any pointers would be greatly appreciated!
These queries are being executed in TBCME v4.2.
Jack
--
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Group "TopBraid Suite Users", the topics of which include
Enterprise Vocabulary Network (EVN), Reference Data Manager (RDM),
TopBraid Composer, TopBraid Live, TopBraid Insight, SPARQLMotion,
SPARQL Web Pages and SPIN.
To post to this group, send email to
topbraid-users@googlegroups.com
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