I have a rather advanced question and there may not be a general solution, but
I'll try anyway...
Problem: Given an arbitrary SPARQL WHERE clause, I want to insert a line
?this a ?SOME_TYPE .
so that it always gets executed "first" - I want ?this to be bound to all
instances of a given class before the rest of the WHERE clause executes. For
example if I have
WHERE {
{
BIND (ex:fun(?this) AS ?result) .
}
FILTER (?result != 1)
}
then I want to programmatically rewrite this to
WHERE {
{
?this a ?SOME_TYPE .
BIND (ex:fun(?this) AS ?result) .
}
FILTER (?result != 1)
}
Is there any clean way of implementing this? My naive approach would be to walk
the open parentheses until I find the first one with a matching closing
parenthesis (or do the equivalent operation on the Syntax tree instead of
strings. Given the policy that SPARQL is executed from the inside out, is this
a safe assumption? Are there alternative approaches to achieving the goal (of
iterating over all instances of a class)? Are there cases where I need to
repeat the binding of ?this in multiple sub-blocks? Or will it be more
efficient to do the iteration "outside" and simply ask the same query for each
instance, with ?this pre-bound with initial bindings?
Thanks a lot
Holger
