Hi Olaf,
many thanks for this detailed bug report. You are 100% right, and I have added
the following line to the clone method
cl.initialBindings = initialBindings;
I believe you have the latest source code so that you can (for now) add this
line yourself, but I am overdue to package all this into a proper next release
of the API. Now that we are getting closer to the 3.4 release of our general
platform, doing a SPIN API release makes a lot of sense.
Thanks and sorry for the inconvenience,
Holger
On Sep 16, 2010, at 7:25 AM, Olaf Hartig wrote:
> Hello,
>
> The method 'clone' of class 'StringPrintContext' in the SPIN API does not
> copy
> the 'initialBindings' member. This causes problems when a query template
> contains placeholders in a FILTER expression. A more detailed description
> follows:
>
> Let's say I have a query template that contains a FILTER expression:
>
> ...
> FILTER (?dep >= ?earliestDep }
> ...
>
> for which the corresponding SPIN description (in Turtle / N3 notation) is
> something like:
>
> ex:myTemplate
> rdf:type spin:Template ;
> spin:body [
> # ...
> sp:where (
> # ...
> [ rdf:type sp:Filter ;
> sp:expression [ rdf:type sp:ge ;
> sp:arg1 _:dep ;
> sp:arg2 _:earliestDep ] ]
> # ...
> )
> ] .
> _:earliestDep sp:varName "earliestDep"^^xsd:string .
>
> Let's say the variable ?earliestDep is a placeholder. Hence, my template
> definition contains something like:
>
> ex:myTemplate spin:constraint [
> rdf:type spl:Argument ;
> spl:predicate ex:earliestDep ;
> spl:valueType xsd:double ] .
>
> Now I instantiate this template. A SPIN description for this instantiation
> could be:
>
> _:myTemplateInstance
> rdf:type ex:myTemplate ;
> ex:earliestDep 4.5 .
>
> For this instantiation I expect the resulting SPARQL query to contain this
> FILTER expression:
>
> ...
> FILTER (?dep >= 4.5 }
> ...
>
> But this does not happen. The placeholder is not replaced by the literal 4.5
> as I would expect. I tracked this problem down: The SPIN API initializes a
> 'StringPrintContext' with the an initial binding that correctly maps the
> earliestDep placeholder to the literal. Then, it prints the body of the
> template to this 'StringPrintContext'. Several print methods are being called
> (recursively) and until -at a certain point- the expression in the FILTER
> clause has to be printed and the method 'printExpressionString' in class
> 'SPINExpressions' is called. Here, the Resource that represents the
> expression
> is casted to a 'FunctionCall', the current print context is cloned, and the
> 'FunctionCall' is printed to the _cloned_ print context. Since the 'clone'
> method of the 'StringPrintContext' does not copy the 'initialBindings', none
> of the arguments of the 'FunctionCall' can be subsituted using the initial
> bindings.
>
> For this reason I propose to copy the 'initialBindings' when a clone of
> 'StringPrintContext' is created.
>
> 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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