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Re: ISSUE-100: Should ld-patch use a slash like sparql does, instead of as it currently does?

From: Andy Seaborne <andy@apache.org>
Date: Mon, 18 Aug 2014 20:38:16 +0100
Message-ID: <53F25628.5060901@apache.org>
To: public-ldp-wg@w3.org
On 18/08/14 17:55, Sandro Hawke wrote:
> On 08/18/2014 09:30 AM, Alexandre Bertails wrote:
>> On Mon, Aug 18, 2014 at 12:00 PM, Sandro Hawke <sandro@w3.org> wrote:
>>> On 08/18/2014 08:17 AM, Alexandre Bertails wrote:

>> The intuition is that when you see `node(s) / p1 / p2`, it means that
>> you start with the current nodes and try to follow p1, this gives you
>> a new set of nodes, on which you can now apply p2.
>
> Same with SPP.

Absolutely.

{ ?x :p1/:p2 ?y }

?x can be a collection of nodes.

Do you have a concrete example of where there are differences?

The charter has a "Liaison" which includes SPARQL WG (tricky as it 
formally does not exist) - why not start by sending a message the SPARQL 
comments list?

	Andy

>> Then you may object that this seems to not work anymore when used in
>> constraints eg. `node(s) / p1 / p2 [ / p3 ]`. Actually, the set of
>> nodes when in a constraint is there *implicitly*, a constraint being
>> exactly like a higher-order function, whose argument is the set of
>> nodes before getting into the constraint.
>
> I'm not concerned with constraints for the purposes of issue-100.
>
>> / is used consistently in the whole path, including its semantics.
>
> I'm not saying it's internally inconsistent, just that it's gratuitously
> different from SPP, as far as I can tell.
>
> I think it's very important that we borrow whichever bits of SPP work
> reasonably well for LD-Patch.
>
>> Now again, same argument as last email, changing that would be a -0.9
>> for me.
>>
>>> The semantics are (arguably) the same; the syntax is extremely similar,
>>> differing only in the leading slash.
>>>
>>> To me that difference is a show-stopper.  That's ISSUE-100.
>> A show-stopper? As in -1 or -0.9 ?
>
> I'm not going to -1 any design decisions here, but I think it's critical
> to answer the questions I raise above.  I'm entirely confident we'll
> have to answer them later with this design, and at that point it'll be
> much harder.
>
>         - s
>
>> Alexandre
>>
>>>        -- Sandro
>>>
>>>
>>>
>>>> But unlike SPARQL, LD path expressions can be nested, and include
>>>> constraints. SPARQL does that with FILTER and new constraints in the
>>>> BGP. The grouping in SPARQL (using parenthesis) is very different from
>>>> the constraints (square brackets and exclamation mark).
>>>>
>>>> I think it's a bad idea to make them feel like they behave the same,
>>>> which could be induced by the choice of the syntax.
>>>>
>>>> I don't want to stop the group with syntactical questions thought, so
>>>> just a -0.9 for me.
>>>>
>>>> Alexandre
>>>>
>>>> [1]
>>>> https://dvcs.w3.org/hg/ldpwg/raw-file/ldpatch/ldpatch.html#path-expression
>>>>
>>>>
>>>> On Mon, Aug 18, 2014 at 10:59 AM, Linked Data Platform  Working Group
>>>> Issue Tracker <sysbot+tracker@w3.org> wrote:
>>>>> ISSUE-100: Should ld-patch use a slash like sparql does, instead of
>>>>> as it
>>>>> currently does?
>>>>>
>>>>> http://www.w3.org/2012/ldp/track/issues/100
>>>>>
>>>>> Raised by:
>>>>> On product:
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>
>
Received on Monday, 18 August 2014 19:38:45 UTC

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