Re: EXISTS : ways forward

On 09/22/2016 05:07 AM, james anderson wrote:
> good afternoon;
> 
>> On 2016-09-22, at 13:46, Andy Seaborne <andy@apache.org
>> <mailto: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.

I don't understand what you mean by "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.

The definition of EXISTS actually works in the SPARQL algebra, not in 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.

I don't understand this.  Could you please explain?

> best regards, from berlin,
> ---
> james anderson | james@dydra.com <mailto:james@dydra.com> | http://dydra.com

peter

Received on Thursday, 22 September 2016 16:19:37 UTC