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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 21:11:56 +0100
Message-ID: <53F25E0C.4050100@apache.org>
To: public-ldp-wg@w3.org
On 18/08/14 20:49, Alexandre Bertails wrote:
> On Mon, Aug 18, 2014 at 3:38 PM, Andy Seaborne <andy@apache.org> wrote:
>> 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?
>
> I think there is some misunderstanding.
>
> In `Bind ?foo ?x /:p1/:p2 .`, ?x is replaced by its previously bound
> value. It is never left unknown and start with a concrete value. The
> operation carries a set of nodes, the final value being here bound to
> ?foo. No need for a solution mapping.

I didn't mention solution mappings.

My point is that in SPARQL path starts from a collection of nodes like 
LD Patch path so the intuition you mention is the same.

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

	Andy

>
>>
>> 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?
>
> I am not sure what we would ask to the SPARQL WG. The LD Patch
> semantics don't share much with SPARQL.

The path syntax overlaps.

>
> Alexandre
>
>>
>>          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 20:12:26 UTC

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