On 3/7/2014 1:55, Nikolaos Beredimas wrote:
So I've been playing around with TBC trial (v 4.1) to find out more
about SPIN.
My problem came about when trying to create a constraint to validate
that a given property's object is an xsd:string exactly 11 characters long
So I wrote this constraint:
# aString Length must be 11
ASK WHERE {
?this :aStringValue ?val1 .
BIND (fn:string-length(?val1) AS ?aStringLength) .
FILTER (?aStringLength != 11) .
}
Weird, this should work. In general through if you are experiencing
unexpected behavior with ordering of BIND and FILTER, keep in mind that
the SPARQL engine may execute things in a different order than you
assume. The SPARQL Debugger can shed some insights into what's happening
under the hood. To force the query order above (BIND before FILTER, wrap
the stuff that shall be executed "first" with a { ... } block such as in
ASK WHERE {
{
?this :aStringValue ?val1 .
BIND (fn:string-length(?val1) AS ?aStringLength) .
}
FILTER (?aStringLength != 11) .
}
PS. Any way to define a kind of priority for evaluation of different
constraints??? Say for example I have one constraint that checks
string length, and one that validates a string's checksum. How should
I implement if I only want to attempt to validate the checksum only if
the string length is valid?
The only way to bypass a constraint check is to duplicate the logic of
the the previous constraint, e.g. turn the constraint above into a SPIN
function that returns true or false, called ex:isStringLengthNot11. Then
put a "guard clause" into the beginning of your other constraint, e.g.
ASK WHERE {
{
FILTER !ex:isStringLengthNot11(?this) .
}
... do the real tests - will only be executed if the first
constraint was not checked
}
The role of the SPIN function is to encapsulate the logic so that you
don't need to write it over and over again.
HTH
Holger
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