Thanks, Tom. Inline...

On 7/3/15 10:35 AM, Tom Johnson wrote:
> Hi Karen,
>
> I'm trying to get back up to speed post-vacation.
>
> At first glance, Holger's "left side" diagram looks okay to me. I'd
> quibble about the terminology---I think what he's really talking about
> is the SPARQL Semantics (as opposed to a SPARQL Engine, which seems like
> an implementation detail which can vary) interfacing with a
> Dataset---but without digging too deep, this seems like a good approach.
> It avoids the need for a new query semantics except with respect to the
> Shapes Graph, but allows SHACL functions to sit in a layer above.

Holger is indeed talking about a SPARQL engine, as I understand his 
statements, and he has already implemented it as a SPARQL Engine. 
However, note that the group is pretty evenly split on this issue, with 
some feeling that SHACL must be solely an extension to SPARQL, with 
Holger's approach, allowing SHACL to be independent of SPARQL, 
considered too liberal to work well.

I sent a link to Active Triples to another person in the group and the 
answer I got was that this would require a different SHACL engine than 
the one being envisioned, and that engine would not be able to implement 
all of SHACL, and therefore: why would we not want to implement a SPARQL 
engine? I don't have an answer to that, but essentially a non-SPARQL 
approach is seen as counter to the spec in at least some areas.

If we think this is important, then someone other than me needs to step 
in and make the case. Issue-47[1] is at the crux of this in some way, 
which is why we took a straw vote on it (inconclusive). I'm at a loss to 
say which approach we prefer because I don't understand the issue. It 
seems to be fundamental to how the standard would work. This seems to be 
related to another issue[2] which asks whether the SHACL graphs and the 
instance data must be in the same graph or not (also no conclusion from 
the group).

If you can do some reading and lend a hand, that would be great. 
Otherwise, we'll just get what we get -- it depends on how much it 
matters to us.

Thanks again,
kc

[1] http://www.w3.org/2014/data-shapes/track/issues/47 (Should SHACL 
require that the shape graph be accessible when evaluating constraints 
on the data graph?
[2] http://www.w3.org/2014/data-shapes/track/issues/30


>
> I think the concerns I would have are as follows:
>
>    - that the SHACL spec would be overly prescriptive, saying that the
> graph(s) to be validated need actually live behind a SPARQL endpoint.
>    - that the SHACL layer itself will defer too much to SPARQL, causing
> it lack appropriate semantics for expressing constraints rather than
> queries.



>
> The first concern is manifest in the "right side" diagram, but not in
> the left. The second applies equally to both, but is not inherent in either.
>
> My feeling is that we should give our support to Holger's argument, and
> press the second point whatever the outcome.



>
> - Tom
>
> On Fri, Jul 3, 2015 at 9:19 AM, Karen Coyle <[log in to unmask]
> <mailto:[log in to unmask]>> wrote:
>
>     Just to follow up -- I've been corresponding with one of the group
>     members and there is strong resistance to have SHACL be workable
>     without SPARQL. We are in a minority in preferring a non-SPARQL
>     solution, so I need ammo for this.
>
>     kc
>
>
>     On 7/2/15 12:37 PM, Karen Coyle wrote:
>
>         I just got off the W3C call and it was a bit of a disaster, and
>         I don't
>         think I helped. So I need some advice on this, and I will try to
>         clear
>         things up in email to W3C group.
>
>         Please look at:
>
>         https://lists.w3.org/Archives/Public/public-data-shapes-wg/2015Jun/0159.html
>
>
>         and in particular at the diagram at the bottom. [1]
>
>         You can see the options in the quoted email just above the
>         diagram. I
>         admit that I do not understand the import of this question, but
>         it is a
>         key one blocking the group. I do not know if this relates to the
>         discussion we had today on our call (I'll send notes about that
>         next) in
>         which it was stated that for some purposes it does not matter
>         how the
>         validation routine forms or identifies a graph. However, it
>         seems that a
>         significant number of functions of SHACL may depend on the question
>         addressed in this email.
>
>         Any clarification in relation to DCMI requirements would be greatly
>         appreciated.
>
>         Thanks,
>         kc
>         [1] The issue for this is
>         http://www.w3.org/2014/data-shapes/track/issues/47, but as you
>         can see,
>         there is a great amount of email, and much discussion has taken
>         place
>         under other subject headers, so I couldn't even give a full list of
>         relevant emails, but they are too many to read anyway.
>
>
>     --
>     Karen Coyle
>     [log in to unmask] <mailto:[log in to unmask]> http://kcoyle.net
>     m: 1-510-435-8234 <tel:1-510-435-8234>
>     skype: kcoylenet/+1-510-984-3600 <tel:%2B1-510-984-3600>
>
>
>
>
> --
> -Tom Johnson

-- 
Karen Coyle
[log in to unmask] http://kcoyle.net
m: 1-510-435-8234
skype: kcoylenet/+1-510-984-3600