[Crm-sig] Properties of properties in RDF

Martin Doerr martin at ics.forth.gr
Thu Mar 15 17:17:22 EET 2018


Dear Conal,

Got it! Yes, subproperties of P01/P02 create an additional constraint, 
which obviously must hold. The reasoning that the PC class expands the 
equivalent property can only be modeled by an OWL rule.

For practical data entry, this should be hidden to the user by a tool, 
which understands exactly the PC semantics. Otherwise the user will be 
drowned under a hundred properties that only enforce obvious 
constraints. This is why we hesitated to publish it in such an expanded 
form.

I meant another issue: If the ".1" property declares a more specific 
type, the relationship between free typing of the base property versus 
creating subproperties of it should be better determined. Other 
properties of properties do not create such problem.

Imagine a fully developed hierarchy of role terms for the P14, with 
broader and narrower terms, such as "as designer" and "as architectural 
sketcher", and then someone declaring a subproperty of P14  called 
"designed by", but not "as architectural sketcher". Then, the 
equivalence of "designed by" and "as designer" could be declared by 
additional OWL rules, as well as that "as architectural sketcher", 
because of being narrower term of "as designer", also implies "designed by".

But, even without and not so badly, at least when declaring for PC14 "as 
designer", and when using "designed by", both declarations will result 
in a P14 link. So, P14 provides the common recall, but not the precision.

You may understand, why for many years I suggested people to create and 
share local subproperty vocabularies for the .1's, which saves a whole 
reasoning engine in the background, but, admittedly, is not as flexible.

But, the problem is analogous to the P2 has type.

All the best,

Martin

On 3/15/2018 1:51 PM, Conal Tuohy wrote:
> Dear Martin
>
> I'm not sure what you meant by "partially declared subproperties" 
> there (the ambiguity of the term "subproperty" in this discussion 
> doesn't help). I think I understood the rest of what you were saying, 
> though.
>
> To be clear, all I was saying was that I would prefer not to publish 
> RDF that directly uses those generic RDF predicates P01_has_domain and 
> P02_has_range, but instead to use a set of more specific predicates 
> (which could be defined to be (RDFS) subproperties of those two 
> predicates). So each distinct type of CRM property which had been 
> reified as an RDFS class (e.g. PC14_carried_out_by) would have its own 
> pair of RDF properties for linking to instances of its domain and range.
>
> My rationale for that preference is that it would be more meaningful 
> to users to make use of an RDF predicate called Pxxx_has_actor (with a 
> domain of PC14_carried_out_by and a range of E39_Actor) and 
> Pxxx_has_activity (with domain PC14_carried_out_by and range 
> E7_Activity), rather than using generic predicates P01_has_domain and 
> P02_has_range. Plus it would give us more type-safety. It would be a 
> trivial extension to that existing RDFS to add those extra RDFS 
> subproperties (about 60 of them, including the inverses).
>
> Regards
>
> Conal
>
> On 15 March 2018 at 20:37, Martin Doerr <martin at ics.forth.gr 
> <mailto:martin at ics.forth.gr>> wrote:
>
>     Dear Conal,
>
>     There is no conflict with adding subproperties. Once we have
>     defined in FOL the logic of properties of properties, each PC
>     class implies its base property. Hence, logically, the subproperty
>     and any added ".1" will hold for the instances declared and imply
>     the same base property. If, at any time we wish to connect term
>     hierarchies of roles for the .1 properties with partially declared
>     subproperties, we need a straight-forward extension of the CRM.
>     Any subproperty, e.g., may refine domain and range.
>
>     All the best,
>
>     Martin
>
>
>     On 3/15/2018 6:28 AM, Conal Tuohy wrote:
>>     Thanks Martin, for the link to
>>     http://www.cidoc-crm.org/sites/default/files/CRMpc_v1.1_0.rdfs
>>     <http://www.cidoc-crm.org/sites/default/files/CRMpc_v1.1_0.rdfs>
>>
>>     This is actually very close to (and compatible with) the approach
>>     I suggested in my earlier email, and I'm embarrassed to say I
>>     wasn't aware of it at all.
>>
>>     I've managed to find some background material (though I had to
>>     use Google to find it!)
>>
>>     http://www.cidoc-crm.org/Issue/ID-266-reified-association-vs-sub-event
>>     <http://www.cidoc-crm.org/Issue/ID-266-reified-association-vs-sub-event>
>>     is an archive of a relevant discussion.
>>
>>     http://www.cidoc-crm.org/sites/default/files/Roles.pdf
>>     <http://www.cidoc-crm.org/sites/default/files/Roles.pdf> presents
>>     a few slides showing options for modelling properties of
>>     properties, including the "Property Class" approach.
>>
>>     These slides include a nice illustration of the approach defined
>>     in the RDFS:
>>
>>     http://www.cidoc-crm.org/sites/default/files/20160802PropertiesOfProperties.pptx
>>     <http://www.cidoc-crm.org/sites/default/files/20160802PropertiesOfProperties.pptx>
>>
>>     I think I'd be very happy with this "Property Class" approach,
>>     although rather than using the generic properties P01_has_domain,
>>     P02_has_range, and their inverses,I would still want to define
>>     specific subproperties, e.g. for the case of actors playing a
>>     specific role in the performance of an activity, I would prefer
>>     to link the performance (i.e. the instance of PC14 carried out
>>     by) to the actor and the activity using domain-specific
>>     properties such as has_actor and has_activity.
>>
>>     Conal
>>
>>     On 15 March 2018 at 04:25, Martin Doerr <martin at ics.forth.gr
>>     <mailto:martin at ics.forth.gr>> wrote:
>>
>>         Dear All,
>>
>>         Please
>>         see:http://www.cidoc-crm.org/sites/default/files/CRMpc_v1.1_0.rdfs
>>         <http://www.cidoc-crm.org/sites/default/files/CRMpc_v1.1_0.rdfs>
>>         on page http://www.cidoc-crm.org/versions-of-the-cidoc-crm
>>         <http://www.cidoc-crm.org/versions-of-the-cidoc-crm>, plus
>>         the issues discussing the solution for version 6.2 (I'll look
>>         for all references).
>>
>>         Best,
>>
>>         martin
>>
>>
>>         On 3/14/2018 12:49 PM, Conal Tuohy wrote:
>>>
>>>
>>>         On 8 March 2018 at 18:02, Richard Light
>>>         <richard at light.demon.co.uk
>>>         <mailto:richard at light.demon.co.uk>> wrote:
>>>
>>>             I was thinking last night that maybe we should focus our
>>>             RDF efforts on exactly this issue: the representation of
>>>             the CRM primitive classes E60, E61 and E62 in RDF.  The
>>>             current RDF document is becoming quite wide-ranging in
>>>             its scope, and (for example) you have questioned whether
>>>             certain sections belong in it.  If we concentrate on
>>>             this single aspect of the broader RDF issue, I think we
>>>             can produce something which is of practical value
>>>             relatively quickly.  In particular, I would like to
>>>             devote time to this during the Lyon meeting.
>>>
>>>         I applaud the idea of focusing narrowly on something so as
>>>         to produce some of practical value quickly!
>>>
>>>         But I do hope that the other issues raised in that document
>>>         will not be set aside too long, or lost.
>>>
>>>         In particular, it seems to me that the mapping from the
>>>         CRM's "properties of properties" to RDF is actually a more
>>>         serious gap.
>>>
>>>         In the CRM, there are a number of properties which are
>>>         themselves the domain of properties. In RDF, however, a
>>>         property does not have properties of its own. Incidentally,
>>>         I remember years ago being able to model this directly in
>>>         ISO Topic Maps, but practical considerations of
>>>         interoperability and community dictate that RDF, despite its
>>>         simpler model, is the technology of choice today.
>>>
>>>         One example of the issue is how to model the role that
>>>         individuals play in events. If a concert performance X was
>>>         P14 carried out by person Y, then this maps naturally to an
>>>         RDF triple in which the predicate is crm:P14_carried_out_by.
>>>         However, if the person carried out that activity in a
>>>         particular role (e.g. as a saxophonist) then things are more
>>>         difficult. In the CRM, the P14_carried_out_by itself has the
>>>         property P14.1_in_the_role_of, whose value could be an
>>>         instance of E55_Type: Saxophonist. This is pleasingly
>>>         consistent with how the CRM handles taxonomies in other
>>>         parts of the model, but it is not workable in RDF because
>>>         the P14_carried_out_by property cannot itself have a property.
>>>
>>>         There are a number of "work-arounds" to this issue, such as
>>>         simplying ignoring the problem and "dumbing down" the data,
>>>         or moving the locus of classification from the property to
>>>         the property value (e.g. in this case that would mean
>>>         classifying the person rather than their role; that doesn't
>>>         work very well because people may have many distinct roles,
>>>         but it works better for other cases).
>>>
>>>         The existing guidance would suggest defining a new
>>>         "saxophone-played-by" property to be a rdfs:subpropertyof
>>>         P14_carried_out_by. This can certainly work, but it's
>>>         actually a poor expression of the CRM's model. It negates
>>>         the practical benefits of having external taxonomies for
>>>         this kind of classification. This guidance, in my opinion,
>>>         makes too much of the apparent similarity between the CRM's
>>>         properties and RDF properties. They are not in fact the same
>>>         kind of thing, and a property which itself bears properties
>>>         is more closely approximated in RDF not as a property but
>>>         reified as a subject resource in its own right. A more
>>>         faithful mapping of the CRM's abstract model to RDF would
>>>         introduce a new RDFS class corresponding to the performance
>>>         of the activity. We could then say that concert performance
>>>         X was P14a_performed_in Performance Z; that Performance Z
>>>         was P14b_carried_out_by person Y, and that Performance Z was
>>>         P14.1_in_the_role_of Saxophonist.
>>>
>>>         That's just one example of the general problem; there are a
>>>         number of others, which are listed here in the context of
>>>         the Linked Art project:
>>>         https://github.com/linked-art/linked.art/issues/55
>>>         <https://github.com/linked-art/linked.art/issues/55> along
>>>         with a variety of options for dealing with the issue.
>>>
>>>         In my opinion the current situation with respect to
>>>         properties of properties (in RDF) is really quite
>>>         unsatisfactory and could be substantially improved by a more
>>>         consistent treatment across the entire schema.
>>>
>>>
>>>
>>>
>>>         -- 
>>>         Conal Tuohy
>>>         http://conaltuohy.com/
>>>         @conal_tuohy
>>>         +61-466-324297 <tel:0466%20324%20297>
>>
>>
>>         -- 
>>         --------------------------------------------------------------
>>           Dr. Martin Doerr              |  Vox:+30(2810)391625        |
>>           Research Director             |  Fax:+30(2810)391638        |
>>                                         |  Email:martin at ics.forth.gr <mailto:martin at ics.forth.gr>  |
>>                                                                       |
>>                         Center for Cultural Informatics               |
>>                         Information Systems Laboratory                |
>>                          Institute of Computer Science                |
>>             Foundation for Research and Technology - Hellas (FORTH)   |
>>                                                                       |
>>                         N.Plastira 100, Vassilika Vouton,             |
>>                          GR70013 Heraklion,Crete,Greece               |
>>                                                                       |
>>                       Web-site:http://www.ics.forth.gr/isl            |
>>         --------------------------------------------------------------
>>
>>
>>
>>
>>     -- 
>>     Conal Tuohy
>>     http://conaltuohy.com/
>>     @conal_tuohy
>>     +61-466-324297 <tel:0466%20324%20297>
>
>
>     -- 
>     --------------------------------------------------------------
>       Dr. Martin Doerr              |  Vox:+30(2810)391625        |
>       Research Director             |  Fax:+30(2810)391638        |
>                                     |  Email:martin at ics.forth.gr <mailto:martin at ics.forth.gr>  |
>                                                                   |
>                     Center for Cultural Informatics               |
>                     Information Systems Laboratory                |
>                      Institute of Computer Science                |
>         Foundation for Research and Technology - Hellas (FORTH)   |
>                                                                   |
>                     N.Plastira 100, Vassilika Vouton,             |
>                      GR70013 Heraklion,Crete,Greece               |
>                                                                   |
>                   Web-site:http://www.ics.forth.gr/isl            |
>     --------------------------------------------------------------
>
>
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>
>
>
>
> -- 
> Conal Tuohy
> http://conaltuohy.com/
> @conal_tuohy
> +61-466-324297


-- 
--------------------------------------------------------------
  Dr. Martin Doerr              |  Vox:+30(2810)391625        |
  Research Director             |  Fax:+30(2810)391638        |
                                |  Email: martin at ics.forth.gr |
                                                              |
                Center for Cultural Informatics               |
                Information Systems Laboratory                |
                 Institute of Computer Science                |
    Foundation for Research and Technology - Hellas (FORTH)   |
                                                              |
                N.Plastira 100, Vassilika Vouton,             |
                 GR70013 Heraklion,Crete,Greece               |
                                                              |
              Web-site: http://www.ics.forth.gr/isl           |
--------------------------------------------------------------

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