Re: First meeting of our group

On 12/11/18 12:03 PM, Doerthe Arndt wrote:
>
> Dear all,
>
> Now that Dave offered to provide us a W3C git (thank you once again!), 
> we should move on to the next point and identify the topics we want to 
> work on. I set up a doodle to find the right time for a  first 
> meeting. Based on your answers so far, I thought that 16:00 UCT was 
> the best time for such a meeting but if you think differently just let 
> me know and I will adapt the doodle:
>
> https://doodle.com/poll/h7xrxhuwfvy8aqmu
>
> The list of open topics we discovered so far was (note that is an open 
> list, I just summarize here what I remember):
>
>   * Provide a *formal semantics *for N3, open issues there:
>       o *Implicit quantification:* scoping of universal variables and
>         existential variables (blank nodes)
>       o *Explicit quantification: *what is the scope of @forSome and
>         @forAll? Do we want to allow any URI as variable?
>       o *Meaning of built-in functions: *we need to agree on built-ins
>         we want to see as part of N3 logic and formalise them.
>       o *Meaning of cited formulas: *we need to agree on one
>         formalisation for the meaning of cited formulas.
>       o *Formalisation of a proof calculus *(but this can only be done
>         after fixing the meaning of formulas).
>       o *Lists: *lists are treated differently in RDF and N3 do we
>         want to keep that? than we should clarify the relations of the
>         standards.
>
>
>   * To agree on formal semantics we really should focus on the
>     expected *use cases* and here I would like to get some insights*.
>     *We especially need to know:*
>     *
>       o *Which built-ins do we need?* Candidates are the ones which
>         are already implemented for Cwm
>         (https://www.w3.org/2000/10/swap/doc/CwmBuiltins), or the one
>         identified by the RIF working group
>         (https://www.w3.org/TR/rif-dtb/) or we could also look into
>         the different functions which are available in SPARQL filters.
>       o *How do want to use cited graphs: *There is a whole list how
>         the related concept TriG could be understood
>         (https://www.w3.org/TR/rdf11-datasets/). Behind these there
>         are for sure applications which drove the definition*s *and I
>         think it could help to understand what these were. But I also
>         think that all of you have ideas how to use the concepts, so
>         maybe we could create examples?*
>         *
>       o *How expressive does the rule reasoning need to be? *This will
>         influence how we formalise the quantification, so I would like
>         to know where you want to use N3 reasoning for.
>
>
>   * We should also keep the *relation to other standards* close:
>       o we should try to align with RDF where possible
>       o do we need a JSON-LD specification?
>       o what is the position towards TriG? Reification? RIF?
>

Hi folks,

My own interest is in making it practical (even fun and easy) to base 
real applications on open-world data (that is, RDF or other KR data), so 
that we end up with a full data-sharing ecosystem. It has long seemed 
like rules were a promising approach: rather than than having to code 
around all the possible forms the input data could take, we simply write 
the appropriate rules and let the system match them to the input data 
whenever/however possible.  I've built a variety of systems like this, 
and in my experience, the promise has not worked out terribly well.  
Rules are very, very hard to debug. Hopefully things will improve some day.

N3, as implemented in cwm, was an attempt to attack the problem by one 
person (with some advice from a few others -- I don't mean to minimized 
DanC's role, but I think he'd agree the vision was Tim's) who had no 
experience with existing rule-based system or familiarity with the 
literature, so the design ended up rather idiosyncratic. At the other 
end of the spectrum, RIF was an attempt to attack this problem by a 
committee which included experts in many different kinds of rule-based 
systems, so it ended up rather complicated and full of options.  I 
joined Tim's group a few weeks after cwm started, in late 2000 and was 
staff contact for RIF from chartering 
<https://www.w3.org/2005/rules/wg/charter> through Recommendation 
<https://www.w3.org/TR/rif-overview/>. I might be the only person 
involved in both projects.

I'd love to see something simple and elegant enough it actually catches 
on. I highly doubt that will be classic N3, in all its self-referential 
glory (the "implies" operator is just an RDF predicate!), or RIF, in all 
its complexity.

If this group just wants to nail down N3, more or less as implemented in 
cwm (and perhaps EYE), then more power to it, I wish it well.  I'll try 
to follow the progress from time to time.

On the other hand, I rather hope it ends up evolving into a language 
which really fits the needs of application developers. That would be 
awesome.

>
>   * Together with the formalisation we should also discuss whether we
>     provide a reference implementation together
>

In general, in standards work, reference implementations are not a great 
idea. It's much better, if possible, to have multiple independent 
implementations and a shared test suite.  Every substantive decision by 
the group -- that is, a decision that might affect whether some 
implementation conforms to the spec -- as well as every normative 
statement in the spec should be recorded as multiple tests added to the 
test suite, showing the correct way for reasoners to behave.  For a rule 
language, positive-entailment and negative-entailment tests are most of 
what you probably want.  Of course there are also positive-syntax and 
negative-syntax tests. See, for example, https://www.w3.org/TR/rif-test/

Best of luck,

    -- Sandro

>  *
>
> I would like to add these topics to the git as soon as we have it, we 
> can also all propose new issues, discuss them there and prioritize. I 
> hope that we end up with a short list of things we all tackle together.
>
> So, for a first step, please fill in the doodle till the end of the week.
>
> Kind regards,
> Doerthe
>
>
> -- 
> Dörthe Arndt
> Researcher Semantic Web
> imec - Ghent University - IDLab | Faculty of Engineering and Architecture | Department of Electronics and Information Systems
> Technologiepark-Zwijnaarde 19, 9052 Ghent, Belgium
> t: +32 9 331 49 59 | e:doerthe.arndt@ugent.be