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Re: Shapes/ShEx or the worrying issue of yet another syntax and lack of validated vision.

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Fri, 18 Jul 2014 01:21:38 -0700
Message-ID: <53C8D912.80202@gmail.com>
To: Jose Emilio Labra Gayo <jelabra@gmail.com>
CC: Karen Coyle <kcoyle@kcoyle.net>, "public-rdf-shapes@w3.org" <public-rdf-shapes@w3.org>
On 07/18/2014 01:12 AM, Jose Emilio Labra Gayo wrote:
> On Fri, Jul 18, 2014 at 9:49 AM, Peter F. Patel-Schneider
> <pfpschneider@gmail.com <mailto:pfpschneider@gmail.com>> wrote:
>
>     So you are saying that ShEx is ambiguous as to whether open or closed
>     semantics is to be applied?  That seems to be a problem with the ShEx
>     definition.
>
>
> No, I am saying that there are two ways to implement Shape expressions...one
> with the open shapes that allows remaining triples and one with closed shapes
> which disallows them.

That's what I said, I think.

> The first implementation from Eric chose open shapes, while in my Shexcala
> implementation I chose closed shapes.
>
> However, once I implemented it, I noticed that it was very easy to handle also
> open shapes...and now, I have a flag in Shexcala so a user can select open vs
> closed shapes when validating.
>
> In the future, my opinion would favour to have both open and closed shapes
> with some syntax that allows one to indicate which one he prefers. For
> example, I would propose:
>
> <A> { :a . }
>
> to be an open shape...it can have property :a with any value and other
> remaining triples
>
> and
>
> <A> [ :a . ]
>
> to be a closed shape...it can have property :a and only property :a, and no
> other remaining triples.
>
> In fact, this distinction between open and closed shapes is similar to regular
> expressions (it is not a coincidence, given that ShEx is based on regular
> expressions) where you can express that you can have an open regex like: "aa"
> or a closed one like "^aa$"
>
> Best regards, Jose Labra
>
>
>     peter
>
>
>
>     On 07/17/2014 02:05 PM, Jose Emilio Labra Gayo wrote:
>
>
>              On 7/16/14, 9:38 PM, Holger Knublauch wrote:
>
>                  Most people in my experience don't care about open world
>         semantics, but
>                  of course nobody would admit that because it's against the
>         specs and
>                  thousands of academic papers.
>
>
>              The cultural heritage community cares deeply about open world
>         semantics.
>              This community has a tradition of creating primarily
>         public-facing data
>              and, even in pre-Web eras, sharing that data widely. For the cultural
>              heritage community, the public, open web is the primary target
>         for its data.
>
>              You confirm for me the impression that much of the discussion
>         here is in
>              the context of enterprise data systems. I will, however, do my
>         best to
>              keep the open world visible in these discussions.
>
>
>         I don't think that those 2 visions (open & closed world) are
>         incompatible. As
>         Kendall Clark noticed, constraint checking can also be combined with Open
>         World systems. One goal of Shape Expressions is to help in the
>         integration of
>         heterogeneous systems in an Open World.
>
>         In fact, one of the first points in the discussion of ShEx was the
>         possibility
>         to declare open shapes instead of closed ones. The difference is that in a
>         declaration like:
>
>         <PersonShape> { foaf:name xsd:string }
>
>         and with the triples:
>
>         :john foaf:name "John" .
>
>         :mary foaf:name "Mary";
>                    foaf:mbox <mailto:mary@m.com <mailto:mary@m.com>
>         <mailto:mary@m.com <mailto:mary@m.com>>> .
>
>
>         a system with open shapes would assign both :john and :mary the shape
>         <PersonShape> because both have :foaf:name, while a system with closed
>         shapes
>         would only assign :john that shape, because :mary has an extra triple.
>
>         Eric's implementation employs Open shapes, while Shexcala first employed
>         closed shapes and now admits both.
>
>         In my opinion, closed shapes are good when you really need to ensure
>         that your
>         graph contains some triples and only those triples, while open shapes are
>         better in an Open World where you want to ensure that your graph has some
>         shape (if it has the triples declared in the shape) but it could also have
>         some remaining triples.
>
>         So as a general remark, I really think the cultural heritage domain
>         can be a
>         very nice use case where the needs of integrating data from different
>         RDF data
>         portals appear.
>
>         Best regards, Jose Labra
>
>
>
>              kc
>              --
>              Karen Coyle
>         kcoyle@kcoyle.net <mailto:kcoyle@kcoyle.net> <mailto:kcoyle@kcoyle.net
>         <mailto:kcoyle@kcoyle.net>> http://kcoyle.net
>              m: 1-510-435-8234 <tel:1-510-435-8234> <tel:1-510-435-8234
>         <tel:1-510-435-8234>>
>
>              skype: kcoylenet
>
>
>
>
>         --
>         Saludos, Labra
>
>
>
>
> --
> Saludos, Labra
Received on Friday, 18 July 2014 08:22:07 UTC

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