On 03/09/14 15:02, Miguel Bento Alves wrote:
Hi Andy,
My idea is replace any “&” by a internal valid variable, ensuring that this
variable does not exist in command. For instance,
…
group by ?x
having (count(1) >=&n)
\\\SPARQL).
...
will be replaced by
group by ?x
having (count(1) >=?OV_A8y7AbAA)
\\\SPARQL).
After I parse the command and I extract all variables used. If miss some
variable that I replace I assume that was done a bad replacement (in a string,
for instance) and this replacement is canceled.
An alternative is to replace occurrence of a named variable, ?n
I start by this approach but seems very difficult and not clear what is
external variables and what is not.
It will be very useful for an answer to this question:
Which are the valid chars for a variable name? Is there any place where this is
defined?
http://www.w3.org/TR/sparql11-query/#rVARNAME
Miguel
On 03 Sep 2014, at 11:38, Andy Seaborne <a...@apache.org> wrote:
On 02/09/14 23:49, Miguel Bento Alves wrote:
Hi Andy,
&n is illegal SPARQL, ok, but that does not means that can be used to
refer a outer variable? The symbol “&” can appear in a SPARQL command
(excepting in a String)?
If yo udo it that way, then you must replace the &n before passing the string
to the SPARQL parser otherwise it won't parse.
An alternative is to replace occurrence of a named variable, ?n
It depends on the details of "refer to an outer variable" means.
If it is that the outer variable can have a number of values then it's either a
join of the results of the query and a table of values from the rest of the
rule matching or it's a repeated execution with different values of ?n.
Straight substitution of ?n for a string value, passing to the parser and
executing is close but can end up in different results depending on whether ?n
is used nested inside the query, either unprojected from a subquery (it's a
different variable) or in nested OPTIONALs (substitution can violates bottom-up
execution semantics).
It's easier to let the execution engine worry about this.
You can use an initial binding for repeated execution. That avoids the nested
different definition problems. Or add a VALUES clause to the query.
and the symbol “$”?
BTW, I almost finished the development of an engine to evaluate rules
that combines rules terms with sparql commands. To finish, I only
need to define the special char to make reference to outer variables
(for now, and to develop the engine, I'm using a non-valid char).
Miguel
Andy
