Re: EXISTS : ways forward

good afternoon;

> On 2016-09-22, at 13:46, Andy Seaborne <andy@apache.org> wrote:
> 
> […]
> 
> There is a 3rd way which is to truly have bindings of variables as an initial set.  Restrict the range of values at the point a variable in bound.  i.e. in the BGP and any AS usage (noting that BIND(... AS ?VAR) and ?VAR in a earlier/deeper BGP is already illegal in SPARQL generally but not if ?VAR is not in-scope at the point of BIND).


this is the (kind of) semantics which is entailed by the simple goal, to have an exists definition which aims to be consistent with the remainder of the language.
it is straight-forward to define and realize this goal, if the semantics is sited at the correct level of interpretation - that is in the abstract algebra, rather than as a demonstration, that some things can never work, if attempted on the basis of the surface syntax.
in addition, where defined in terms of substitution and scoping rules, it does not introduce a situation, where a definition in terms of a concrete implementation requires one to fulfil “as-if” guarantees for the cases where the stipulated implementation is not feasible.

best regards, from berlin,
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james anderson | james@dydra.com | http://dydra.com