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RE: AW: Thoughts on validation requirements

From: Irene Polikoff <irene@topquadrant.com>
Date: Wed, 30 Jul 2014 11:52:13 -0400
To: "'Eric Prud'hommeaux'" <eric@w3.org>, "'Peter F. Patel-Schneider'" <pfpschneider@gmail.com>
Cc: <public-rdf-shapes@w3.org>, "'Dimitris Kontokostas'" <kontokostas@informatik.uni-leipzig.de>, "'Bosch, Thomas'" <Thomas.Bosch@gesis.org>
Message-ID: <017201cfac0e$3b9f29c0$b2dd7d40$@topquadrant.com>
< I see the multiple somethings as a strong case for detaching the shape
(the way that a particular app is using these types) from the types
themselves. Even if Clinic A and Clinic B are in the same clincal network,
they'll capture different information about e.g. the admitting physician's
credentials.>

The beauty and utility of RDF is that this is not an issue and we can easily
do both. Keep basic information about classes in one graph, constraints
needed by clinic A in another graph that includes the core graph with
classes, constraints need by B in its own graph that also includes by
reference the core graph with classes.

-----Original Message-----
From: Eric Prud'hommeaux [mailto:eric@w3.org] 
Sent: Wednesday, July 30, 2014 10:57 AM
To: Peter F. Patel-Schneider
Cc: public-rdf-shapes@w3.org; Dimitris Kontokostas; Bosch, Thomas
Subject: Re: AW: Thoughts on validation requirements

* Peter F. Patel-Schneider <pfpschneider@gmail.com> [2014-07-29 08:01-0700]
> On 07/29/2014 03:43 AM, Eric Prud'hommeaux wrote:
> >* Peter F. Patel-Schneider <pfpschneider@gmail.com> [2014-07-28 
> >07:54-0700]
> >>On 07/28/2014 02:20 AM, Eric Prud'hommeaux wrote:
> >>>On Jul 28, 2014 12:08 AM, "Peter F. Patel-Schneider" 
> >>><pfpschneider@gmail.com>
> >>>wrote:
> 
> [...]
> 
> >>An RDF document, on the other hand, almost invariably contains 
> >>multiple somethings, very often not arranged in a tree, and 
> >>sometimes even without any connection between them.  In RDF it is 
> >>generally permissable to have any sort of information, whereas XML 
> >>information is generally required to fit into what is expected.
> >
> >I agree, but fear this is a sort of selection bias.
> 
> Well obviously there is a bias towards using RDF for multiple 
> somethings, because RDF is good at that and other formats are not.
> Because of this virtuous bias, there is the concomitant bias that 
> there is relatively less RDF that is used for single somethings.
> There is, of course, nothing wrong with this so far.
> 
> It may be that because RDF is good for multiple somethings, some 
> people think that it is not good for single somethings.  If so, this 
> would be somewhat unfortunate.

Agreed, and that's probably a point that will require constant reminders,
though the cases I'm referring to use multiple somethings, see "Linked Data
Basic Profile 1.0 - Use Cases and Requirements".
<http://www.w3.org/Submission/2012/SUBM-ldbpucr-20120326/#usecases>
Below, Consider a HospitalTransferRecord from Clinic A to Clinic B.
This would incorporate a bunch of somethings like a target problem, vitals,
prescriptions, and a patient (well, more rigorously just a person
temporarily acting in the role of patient).


> However, this certainly doesn't mean that RDF validation should ignore 
> the common situation of multiple somethings, most or all with explicit 
> types.  Nor does it mean that RDF validation should be targeted 
> towards single untyped somethings.  To do either of these is to ignore 
> RDF's strengths.

I see the multiple somethings as a strong case for detaching the shape (the
way that a particular app is using these types) from the types themselves.
Even if Clinic A and Clinic B are in the same clincal network, they'll
capture different information about e.g. the admitting physician's
credentials. In OWL, one would probably capture these as anonymous
restrictions, e.g. ClinicB:AdminissionRecord:

  Class: ClinicB:AdmissionRecord
    SubClassOf: 
      clin:AdmissionRecord,
      clin:admitter only 
        ((clin:credential some (clin:authority only ({"AMA" , "GMC"})))
         and (clin:credential min 1 owl:Thing))


> So I remain very skeptical that ShEx is a viable start towards RDF 
> validation, as it appears to me to be targeted towards an uncommon use 
> of RDF and not easily extended to nicely cover the bulk of extant and 
> proposed RDF.
> 
> >Perhaps the
> >majority of LDP uses include a backend which is not a triple store 
> >(possibly SQL, possibly state stored in the position of a lightswitch 
> >on a wall). In these cases, the data one posts must be limited to the 
> >exact arrangement of somethings that the server expects or data will 
> >be (silently) dropped. I suspect that the majority of the business 
> >use cases on the horizon for RDF involve services that are not 
> >willing to store arbitrary triples.
> 
> Even if true this is at best an argument for validation that covers 
> all (local) triples.  It still doesn't get one from multiple 
> somethings to single somethings.  I'm also still skeptical that 
> covering all (local) triples is a good idea even here, as it would 
> prohibit, for example, extra information coming from a node belonging 
> to an unexpected (or maybe even expected) subtype.
> 
> >>Validation then should work differently in RDF than in XML.  My view 
> >>of RDF validation is determining whether the instances of a type 
> >>(not necessarily explicitly signalled by an rdf:type link) meet some 
> >>constraint, and that RDF validation generally involves multiple 
> >>types, often unrelated types.  I don't see how ShEx can do this, and 
> >>thus my questions as to how ShEx can do RDF validation.
> >
> >What if shapes were types? I think that would meet your definition.
> 
> Well, that's the method used in Stardog ICV, and in lots of work on 
> constraints over logical formalisms (including description logics).


I don't see ShEx has having a problem with multiple somethings. The ShExC
for the above ClinicB:AdmissionRecord could set licensing requirements on
the admitting physician and coding requirements on the principle complaint:

  ClinicB:AdmissionRecord {
    clin:admitter {
      clin:credential { clin:authority ("AMA" | "GMC") }+
    }
    clin:principleComplaint {
      hl7:coding { hl7:CD.CodingSystem ("SNOMED" | "LOINC") }
    }+
  }


> However, just making shapes be types doesn't immediately get one from 
> ShEx to something that can nicely handle multiple somethings in RDF.  
> One also needs machinery to require that each instance of a particular 
> type must match a particular constraint type.

Why do we neet to attach it to a type? Wouldn't that mean that every
reusable object would have to have a bunch of types attempting to predict
all of the ways that data might be used? For instance, would the admitting
physician need to have type arcs asserting that he/she was a
bethIsreal:SurgicalPhysician, bethIsreal:EDAdmittingPhysician,
BOSchildrens:Surgeon, mgh:ThoracicSurgeon, mgh:AdmittingPhysician?

I'd expect that the physician's record should only advertise the type arcs
that are part of some shared ontology:
  <Pat> a foaf:Person , clin:Physician .
If the type arcs are only notionally attached to the data for the purposes
of verification, then the argument that they need to be types is circular;
they're only there because some verification system thinks in terms of
types.


> >There's some language (ShEx, Resource Shapes, Description Set 
> >Profiles or something else whose name I can't recall) to verify that 
> >a node in an instance graph matches a declared structure in a schema. 
> >Some mechanism like oslc:resourceShape associates a graph node with 
> >that structure. Does that fit your view?
> 
> Maybe.  I'm not sure how Resource Shapes 2.0 works, as the description 
> is very loose.  It does appear that typed shapes are what is intended 
> to be used for what I think of as the usual case of RDF validation - 
> requiring that instances of a class have a particular shape.  However, 
> some aspects of Resource Shapes 2.0 appear to be inimical to type 
> hierarchies.

It seems like predicates like oslc:resourceShape give us the duck typing
that we need to get practical interoperability out of our reusable
somethings.


> peter

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-ericP

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Received on Wednesday, 30 July 2014 15:53:05 UTC

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