W3C home > Mailing lists > Public > public-data-shapes-wg@w3.org > January 2015

Re: Shapes are Classes, even if you don't use rdf:type

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Sun, 25 Jan 2015 06:54:34 -0800
Message-ID: <54C503AA.4050108@gmail.com>
To: Jerven Bolleman <jerven.bolleman@isb-sib.ch>, public-data-shapes-wg@w3.org
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If shapes are classes then it is possible to assert that an individual
belongs to a shape, as in

ex:myOffice rdf:type officeShape .

Because it is possible to not belong to a shape, this introduces a new kind
of contradiction (and contradictions are indeed different from constraint
violations).

peter

On 01/25/2015 04:25 AM, Jerven Bolleman wrote:
> Dear Working Group,
> 
> I have tried to keep to the sidelines in this discussion, but as a very 
> interested user of this kind of tech I feel I need to speak out.
> 
> Shapes are Classes, in all practical and theoretical terms [1]. ShEX 
> shapes are just another way to infer class membership (Closed World but 
> otherwise basically OWL all over again)
> 
> Instead of inferring example:A is a member of an owl:Class you now infer 
> that example:A is a member of things that have shape Y. Using the word 
> shape instead of Class is good to avoid confusing between OWL and this 
> standard, but they are the same thing just relabelled.
> 
> 
> The fact that shapes tries to avoid rdf:type at all cost is going to be
> a real problem in even trivial real world cases. e.g.
> 
> example:office example:telNo “+41 41 41 41” .
> 
> example:person example:name “example person” ; example:telNo “+32 32 32 
> 32” .
> 
> <officeShape> { example:telNo xsd:string }
> 
> <personShape> { example:telNo xsd:string example:name xsd:string }
> 
> Is example:office a member of the <personShape> just without a phone 
> number? Yes or No. If it is not clear in this trivial example, how can
> we [tell] end users, reason about it and build stable software?
> 
> LDOM, SPIN and OCLS all solve this by depending on the rdf:type. Its 
> simple and clear cut.
> 
> Now sometimes a direct rdf:type use is not enough or can be confusing. 
> Because, in all proposals what is lacking is associating a 
> shape/constraint with the context in which this constraint should apply. 
> Introducing a new predicate _ldom:context_ which links a resource 
> describing when the constraint could be used.
> 
> e.g. ex:Rectangle a rdfs:Class ; rdfs:subClassOf rdfs:Resource ; 
> rdfs:label "Rectangle" ; ldom:property [ a ldom:PropertyConstraint ; #
> This type declaration is optional ldom:predicate ex:height ; 
> ldom:minCount 1 ; ldom:maxCount 1 ; ldom:valueType xsd:integer ; 
> rdfs:label "height" ; rdfs:comment "The height of the Rectangle.” ; 
> ldom:context ex:Normal_Geometry ;  # Here we say where we intent the 
> context to apply ] . ex:Normal_Geometry rfds:label “Euclidean geometry
> in 2 dimensions” .
> 
> If we give each ldom:property an explicit way to state in which context 
> they apply we can actually deal with different people using foaf:person 
> in multiple manners. e.g. the constraints on foaf:person data being 
> submitted to a restaurant reservation site is different to the 
> constraints on foaf:person data being submitted to a car rental site.
> 
> The LDOM processor can then choose to state which contexts applies to
> its users needs. The default would sensibly be all, and allow users to
> white or black lists to include or exclude contexts as they want.
> 
> This is a much cleaner solution than the shapes one. In shapes we
> attempt to separate the ontologies and their constraints to avoid
> constraint collisions, but we just hope that we don’t import them anyway.
> With this context suggestion, constraint collisions become something we
> can deal with.
> 
> The advantage of attaching a context to constraints is that you can then 
> say something like a post request with RDF data to book the rental of a 
> car requires 1 driver, 1 driver license and 1 payment method. Currently 
> in shapes and ldom, an empty message validates as well :( Plus it allows 
> users to communicate when constraints should hold and when not. e.g. 
> describing the steps in a wizard, step 1 has less constraints  on the 
> submitted data then after step 2.
> 
> 
> Secondly, I do think that ldom should be able to work from predicates as 
> well.
> 
> ex:widthIn_cm a rdf:Property ; rdfs:label “width in centimetre” ; 
> ldom:property [ ldom:valueType xsd:positiveInteger ldom:context 
> ex:realSpace ] .
> 
> Allowing this kind of construct should help the dc:terms case where 
> rdf:types are not specified.
> 
> While modelling from a predicate is not everyone’s cup of tea I find
> that it meshes nicely with the Smalltalk message based OO paradigm, in 
> comparison to the conventional ADT type OO paradigm of Java&C++. Which
> is why I believe it should have a place in this standard.
> 
> Sometimes data does not have types associated with them. In this 
> relatively rare case I humbly suggest that the user use an existing W3C 
> standard to infer a type: namely OWL. And if OWL doesn’t float their
> boat then use a SPARQL update statement. Totally typeless data is rare
> and should not be the primary use case for this WG.
> 
> e.g.
> 
> <officeShape> { example:telNo xsd:string }
> 
> is practically equivalent to
> 
> : officeShape a owl:Class ; rdfs:subClasOf [ a owl:Restriction ; 
> owl:onProperty example:telNo ; owl:minCardinality 1 . ].
> 
> In both cases some kind of reasoning has to take place to determine if 
> the following triple
> 
> example:office example:telNo “+41 41 41 41” .
> 
> means that triples about example:office meet the criteria of 
> <officeShape>.
> 
> Now get back to work and standardise something fantastic !
> 
> Sincere regards, Jerven Bolleman
> 
> [1] If it quacks like a duck and does not carry a shotgun then for all 
> practical purposes it is a duck. All though for our favourite instance 
> example Dick Cheney its “If it quacks like a duck then its a target” ;) 
> even if what quacks wears a bright fluorescent jacket and practices law.
> 
> ------------------------------------------------------------------- 
> Jerven Bolleman                        Jerven.Bolleman@isb-sib.ch SIB 
> Swiss Institute of Bioinformatics      Tel: +41 (0)22 379 58 85 CMU, rue 
> Michel Servet 1               Fax: +41 (0)22 379 58 58 1211 Geneve 4, 
> Switzerland     www.isb-sib.ch - www.uniprot.org Follow us at 
> https://twitter.com/#!/uniprot 
> -------------------------------------------------------------------
> 
> 
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Received on Sunday, 25 January 2015 14:55:10 UTC

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