Hi Olaf,
I have been trying to reproduce this, but so far without success. Judging from
the source code, the variable blank node would have to have an rdf:type while
your example below does not have this. You can also try that this works in
general if you just enter this with TBC (FE) on some resource for property
spin:query (or define a corresponding Template there).
So I may need a more complete test case. I did notice though that if the
rdf:type is sp:Variable, then the existing code might indeed be wrong. But the
parser usually does not create this triple, so I don't think this is the issue.
Thanks,
Holger
On Sep 16, 2010, at 7:47 PM, Olaf Hartig wrote:
> Hello,
>
> There is a problem in the SPIN API with printing an ORDER BY expression that
> contains a query variable.
>
> Let's say I have the following SPIN description of a SPARQL query with an
> ORDER BY clause:
>
> _:myQuery
> rdf:type sp:Select ;
> # ...
> sp:orderBy ( [sp:varName "dep"^^xsd:string] ) .
>
> When I print this query with the SPIN API using the class
> 'StringPrintContext'
> I would expect to get something like:
>
> SELECT ... {
> ...
> }
> ORDER BY ?dep
>
> but what I get is
>
> SELECT ... {
> ...
> }
> ORDER BY (sp:Variable())
>
> I tried to track this problem down. It seems to be in the method
> 'printOrderByExpression' of class 'QueryImpl'. This method is called with a
> Resource which is of rdf:type sp:Variable and it represents the variable. The
> first thing 'printOrderByExpression' with this Resource, it tries to cast it
> to
> a 'FunctionCall' which works. Therefore, it tries to print the variable as if
> it were a 'FunctionCall'.
> I think this problem can be fixed by trying to cast the Resource to a
> 'Variable' before casting it to a 'FunctionCall' and if it turns out to be a
> a
> variable (i.e. if the cast works) then use the functionality to print
> variables.
>
> Greetings,
> Olaf
>
> ----------------------
> Olaf Hartig (http://olafhartig.de)
> Database and Information Systems Research Group
> Department of Computer Science
> Humboldt-Universität zu Berlin
>
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