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

On Fri, Jul 18, 2014 at 9:49 AM, Peter F. Patel-Schneider <
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.

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>> .
>>
>>
>> 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> http://kcoyle.net
>>     m: 1-510-435-8234 <tel:1-510-435-8234>
>>
>>     skype: kcoylenet
>>
>>
>>
>>
>> --
>> Saludos, Labra
>>
>


-- 
Saludos, Labra