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Implementation feasibility (was: Re: Pragmatic Proposal for the Structure of the SHACL Spec)

From: Dimitris Kontokostas <kontokostas@informatik.uni-leipzig.de>
Date: Fri, 20 Mar 2015 10:13:20 +0200
Message-ID: <CA+u4+a0d9A2WGs5uM-j0dccz3i_zJhzJ1ER96F8L2K6KOfswJg@mail.gmail.com>
To: Holger Knublauch <holger@topquadrant.com>
Cc: public-data-shapes-wg <public-data-shapes-wg@w3.org>
On Thu, Mar 19, 2015 at 10:46 PM, Holger Knublauch <holger@topquadrant.com>
wrote:

>  On 3/20/15 2:52 AM, Arnaud Le Hors wrote:
>
> I have to differ on the point that the organization of our documents is up
> to the editors. This is very much a WG decision and there is actually very
> practical consequences that we need to consider and may influence how we
> want to organize our documents.
>
> One of them is that to become a Recommendation a specification needs to
> successfully go through Candidate Recommendation and gather enough
> implementation support (what exactly "enough" means is to be defined by the
> WG but it's a least 2 implementations). If everything is in one document,
> we need to get that  whole document to get enough implementation support to
> become a Recommendation. If we split the document in smaller pieces,
> various pieces might move along at a different pace.
>
> For instance, we might be able to get the higher level set that doesn't
> require support for SPARQL extensions as a REC sooner.
>
> This is also something to consider when thinking about the dependencies
> between the different layers. With the bottom up approach, if we end up
> with the higher level having a normative reference to the lower level it
> won't be able to get to REC until the lower level is. This is also true if
> the higher level is defined as a "profile" (i.e., a specification that
> defines a subset of a full spec) of the main spec.
>
>
> The argument about implementation support is not strong enough. As stated
> TopQuadrant will provide an open source implementation of the full spec
> that is tracking the progress as soon as we decide to go to FPWD state. In
> the IRC log, Dimitris has also announced that he will work on another
> implementation. Finally, while I cannot speak for them, we have at least
> one SPARQL database vendor in our group (I am not sure what happened to
> Arthur Keen, I don't see him on the list anymore). This sounds like at
> least 3 implementations from within the group already, and we still have
> 1.5 years to go.
>

Speaking personally and strictly in terms of implementation feasibility, I
think I could easier implement the currently 'SPARQL extension mechanism'
than the currently suggested 'core' language.

The current spec defines templates and function and RDFUnit already has a
templating mechanism. It is different and more low-level that the one Holger
suggests but I could easily implement it, which leaves only functions which
is kind of similar in complexity.

On the other hand, the core language has features that are harder to
implement (depending on the final details of course)
1) disjunction
2) recursive shapes
3) closed shapes

Looking at the ShEx implementations I also see *possible* trouble in
implementing other features in the 'core' language that are already
implemented in SPIN, RDFUnit & probably ICV
1) type validation (in general but also in terms of disjunction, recursive
& closed)
2) Implementing the Constraint violation vocabulary
2.1) Human readable messages
2.2) severity levels
3) macro functions (let's see what happens to this one)
4) complex constraints

In the current situation I would (personally) be more worried on
implementations for the core language than for the SPARQL extension
mechanism. Unless of course we remove more parts from 'core' but then we
would need a third profile.

To sum up and quoting Richard, before deciding to split documents or not we
should all work together & collaborate.
Personally I would be in favor of keeping everything on one place but I'm
not dogmatic about this. What I suggest is for now keep everything in one
document to keep it coherent and defer the splitting decision for later.

Best,
Dimitris



> Holger
>
>
>
>  --
> Arnaud  Le Hors - Senior Technical Staff Member, Open Web Technologies -
> IBM Software Group
>
>
> Arthur Ryman <arthur.ryman@gmail.com> <arthur.ryman@gmail.com> wrote on
> 03/19/2015 09:15:39 AM:
>
> > From: Arthur Ryman <arthur.ryman@gmail.com> <arthur.ryman@gmail.com>
> > To: Richard Cyganiak <richard@cyganiak.de> <richard@cyganiak.de>
> > Cc: "public-data-shapes-wg@w3.org" <public-data-shapes-wg@w3.org>
> <public-data-shapes-wg@w3.org> <public-data-shapes-wg@w3.org>
> > Date: 03/19/2015 09:16 AM
> > Subject: Re: Pragmatic Proposal for the Structure of the SHACL Spec
> >
> > Richard,
> >
> > I am fine with these parts being in one document if that in fact
> > simplifies maintenance. That decision should be delegated to the
> > editors. However, I think we could stabilize Part 1 soon, publish it,
> > show a heartbeat, and get some feedback.
> >
> > I hope we don't have warring editors. Putting a stake in the ground by
> > publishing Part 1 might improve our shared understanding of SHACL.
> >
> > -- Arthur
> >
> > On Thu, Mar 19, 2015 at 8:02 AM, Richard Cyganiak <richard@cyganiak.de>
> <richard@cyganiak.de> wrote:
> > > Arthur,
> > >
> > > I agree with your analysis regarding different audiences. I am
> > sympathetic to the notion that there should be three parts.
> > >
> > > However, I disagree with your conclusion that there should be
> > three documents.
> > >
> > > Keeping multiple documents in sync is a significant burden on a
> > working group. It makes sense if the documents describe loosely
> > coupled components of an overall framework, but that is not the case
> > here; your proposed split would leave material related to a single
> > language feature often distributed over three different documents
> > (and perhaps maintained by three warring editors).
> > >
> > > I don’t see why a single specification cannot adequately address
> > the needs of different target audiences.
> > >
> > > The SPARQL 1.1 spec is an example of a specification that delivers
> > a primer, a thorough language reference, precise semantics, and
> > guidance for implementers in a single document.
> > >
> > > Best,
> > > Richard
> > >
> > >
> > >
> > >> On 18 Mar 2015, at 22:29, Arthur Ryman <arthur.ryman@gmail.com>
> <arthur.ryman@gmail.com> wrote:
> > >>
> > >> At present we are witnessing a burst of creative activity. It is great
> > >> to see such energy in a WG. However, the result is that we have too
> > >> many specs and I doubt that most members can give all these documents
> > >> adequate review. We need to focus our resources on fewer specs.
> > >>
> > >> There has also been extended discussion on the role of SPARQL, on
> > >> profiles of SHACL, and on who the target audience is. I'd like to
> > >> propose a pragmatic structure that will enable us to package the
> > >> material in a way that will address our audiences, enable us to divide
> > >> the work better, and create a sequence of deliverables.
> > >>
> > >> I propose three levels of content. I'll refer to these as Parts 1, 2,
> > >> and 3 in order to defer word-smithing of the titles.
> > >>
> > >> 1. SHACL Part 1. The audience is people who want to use a simple,
> > >> high-level language that can express common constraints. This document
> > >> should use precise, natural language to describe the semantics of
> > >> those common constraints that can be expressed using the high-level
> > >> vocabulary of SHACL. It should also include simple examples to
> > >> illustrate concepts. It should be readable by people who do not know
> > >> SPARQL. It should not refer to SPARQL. It should not define formal
> > >> semantics. It should be possible for this part of SHACL to be readily
> > >> implemented in SPARQL or Javascript. We therefore need to limit the
> > >> expressive power of this part of SHACL.
> > >>
> > >> 2. SHACL Part 2. The audience is people who want to write custom
> > >> constraints using an executable language. This part defines the
> > >> template/macro mechanism. It also provides normative SPARQL
> > >> implementations of the high-level SHACL language introduced in Part 1.
> > >> This part should not contain other formal specifications. The SPARQL
> > >> implementations can be regarded as executable formal specifications.
> > >>
> > >> 3. SHACL Part 3. The audience is people who want to implement SHACL.
> > >> This part should contain a formal specification. We can defer the
> > >> choice of formalism. If we have multiple candidates and willing
> > >> authors, let's do a bake-off.
> > >>
> > >> -- Arthur
> > >>
> > >
> >
>
>
>


-- 
Dimitris Kontokostas
Department of Computer Science, University of Leipzig
Research Group: http://aksw.org
Homepage:http://aksw.org/DimitrisKontokostas
Received on Friday, 20 March 2015 08:14:16 UTC

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