Hi Olaf,
OK this explains it. In this case, please adjust the following function in
SPINFactory with the extra check to exclude sp:Variable as shown below. I am
including this change in the next release as well (my tests still pass).
I honestly didn't expect anyone to generate SPIN RDF by hand (or with some
other algorithm than the provided SPIN parser), so I may not have tested those
cases. What you did was perfectly valid according to the spec though. If you
have a minute I would be very interested to hear about your use case of the API
in your project (maybe off-list).
Viele Gruesse
Holger
public static FunctionCall asFunctionCall(Resource resource) {
if(resource.isAnon()) {
Statement s = resource.getProperty(RDF.type);
if(s != null && s.getObject().isURIResource() &&
!SP.Variable.equals(s.getObject())) {
return resource.as(FunctionCall.class);
}
}
return null;
}
On Sep 16, 2010, at 8:43 PM, Olaf Hartig wrote:
> Hey Holger,
>
> Yes, it's true. In my system all the blank nodes that represent query
> variables have the rdf:type sp:Variable statement. Hence, the example in my
> bug report was incomplete. Sorry.
> However, now I see that exactly this statement seems to be the cause of the
> problem. Due to this statement the 'asFunctionCall' method incorrectly
> assumes
> the blank node for the variable is a function call and, thus, the cast in
> 'printOrderByExpression' works, which shouldn't. Therefore, the solution to
> try to cast to a Variable before trying to cast to a FunctionCall as I
> propose
> in my report still seems to be suitable.
>
> Greetings,
> Olaf
>
> On Thursday 16 September 2010 11:21:45 Holger Knublauch wrote:
>> 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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