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

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

From: Jerven Bolleman <jerven.bolleman@isb-sib.ch>
Date: Sun, 25 Jan 2015 13:25:03 +0100
To: public-data-shapes-wg@w3.org
Message-Id: <EE731083-B1ED-480E-94A5-4560D2C2DEDD@isb-sib.ch>
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 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
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Received on Sunday, 25 January 2015 12:25:42 UTC

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