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Re: Pragmatic Proposal for the Structure of the SHACL Spec

From: Holger Knublauch <holger@topquadrant.com>
Date: Thu, 19 Mar 2015 13:46:47 +1000
Message-ID: <550A46A7.7000909@topquadrant.com>
To: "public-data-shapes-wg@w3.org" <public-data-shapes-wg@w3.org>
Arthur,

did you have a chance to skim through the current spec draft? Where does 
it not follow the division that you propose? What would you do differently?

You also did not address my question: how could anyone define Part 2 
(templates and SPARQL) without also covering Part 3 (Which is supposed 
to be Section 11 "Supported Operations")?

Thanks,
Holger


On 3/19/2015 12:54, Arthur Ryman wrote:
> Holger,
>
> I understand that this division of content is not what you have been
> advocating. I disagree that specs are only for implementers. I
> frequently consult the SPARQL spec when I am writing queries, but I
> have never implemented a SPARQL engine. Who among has implemented a
> SPARQL engine? Specs are normative and precise. Primers focus on
> progressive disclosure and are pedagogical.
>
> Part 1 is not a primer. It covers the part of SHACL that most users of
> SHACL need to understand (approximately the same level of material
> covered by OSLC Shapes). That part of SHACL can be used without
> requiring any knowledge of SPARQL. That part of SHACL could be
> implemented in other technologies.
>
> Part 2 defines the extension mechanism and uses SPARQL to define the
> precise meaning of constraints expressible in Part 1. Only people who
> understand SPARQL would benefit from reading it.
>
> Part 3 defines the semantics more abstractly and precisely defines the
> aspects of Part 2 that cannot be expressed directly in SPARQL, e.g.
> the higher level control structures. In theory, an implementer who did
> not understand SPARQL would be able to understand SHACL by reading
> Part 3.
>
> We definitely need a primer for Part 1. We probably need a primer for
> some of Part 2. The audience for Part 3 is beyond the need for
> primers.
>
> -- Arthur
>
> On Wed, Mar 18, 2015 at 6:43 PM, Holger Knublauch
> <holger@topquadrant.com> wrote:
>> Hi Arthur,
>>
>> I think your message is mixing up Primer and Spec material. The Spec is
>> meant for implementers. Others can read Primers, examples, mailing lists,
>> stack overflow etc. For now the WG should focus on the Spec.
>>
>> Having said this, I believe my current draft addresses your separation of
>> Part 1 (sections 2-6) and Part 2 (sections 7 onwards) already. I do not see
>> how to separate your Part 3 from Part 2 - as soon as you talk about
>> templates and sh:sparql, you also need to have a precise definition of how
>> these are implemented. This is covered by the Operations section of my
>> draft.
>>
>> Holger
>>
>>
>>
>> On 3/19/2015 8:29, Arthur Ryman 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
>>>
>>
Received on Thursday, 19 March 2015 03:47:56 UTC

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