[Crm-sig] Issue: Solution for Dualism of E41 Appellation and rdfs:label

Richard Light richard at light.demon.co.uk
Thu Sep 13 19:22:59 EEST 2018


On 12/09/2018 14:55, Martin Doerr wrote:
> Dear Richard,
>
> I basically agree with your comments. Specifically however, I indeed
> wanted to say that the official definition of rdfs:label makes it
> exactly a subproperty of P1 (or shortcut of it) in any correct use of
> RDFS. If we want to mix RDFS models, we should have an opinion about
> their compatibility. Otherwise, we would have to regard them as
> alternative that cannot be compared with the CRM.
OK: noted.  My concern is simply that we should not include assertions
which mean that 'CRM RDF' fails to play nicely with other RDF
frameworks.  I would welcome the thoughts of others on this issue.

> I am not happy with adding rdfs:label to instances of Appellation,
> because this would mean it is a name for a name and not the name. I
> would sympathize with George using rdfs:value, if it had the
> respective semantics.
Yes, we're in full agreement on this.

> What we need, to my opinion, is a property of Symbolic Object we may
> call it "has symbolic content" or "has symbolic content inline" or
> anything better, which defines that the symbolic content *is identical
> to* the Literal, *abstracted *to the "level of symbolic specificity"
> that the Literal implies and that conforms to the identity condition
> of the Symbolic Object, i.e., characters of a certain script, or
> whatever. That would make the meaning of the "value" unambiguous.
Again, I'm in complete agreement with this line of thought.  One
decision we should make is whether this property forms part of the
generic CRM framework, or if it is to be an implementation-specific
property which only appears in our RDF implementation of the CRM.  My
instinct is for it to go into the CRM proper: the treatment of Symbolic
Object and its subclasses would I think be made clearer by the addition
of this property.

It's worth bearing in mind that RDF strings have a built-in mechanism
for specifying the language of the string.  This would allow us to
express, for example, a place name in multiple languages by simply
having one 'has symbolic content' property per language, each with an
associated string.

> We may need add another property, such as "is contained in" or so
> pointing to a URL actually holding an instance of its content, again
> abstracted to the "level of symbolic specificity" that the file
> instance implies and that conforms to the identity condition of the
> Symbolic Object.
I think that we would benefit from some use cases which demonstrate the
practical need for this property.  My own instinct is that if we are
really just recording a string value, then it is overkill to assign it a
URL and put it somewhere else.  If it's more than just a string value,
in what way is it more?  Is it an instance of some other class, which we
should be defining (or have already identified)?

My suggestion is that we define the "has symbolic content" property, and
then put our energy into agreeing one or more subproperties of rdf:value
which meet the known recording requirements for cultural heritage
information.  By doing this, I suggest that we will have solved the main
problem which confronts implementors who want to express CRM in RDF.

> Whereas the shortcut interpretation is attractive, it is not exactly
> the same. Using a shortcut, we say that the intermediate node is of
> different, independent nature from the terminal node. Here, we do not
> say "Appellation" is related to something called "Literal". We say
> "this Appellation IS itself what is in this Literal". That may or may
> not be a reason to reject this interpretation.
True.  At least two respondents in this conversation have said that they
prefer the fully-worked-out paths.  Let's sort out an initial strategy
for RDF based on the current CRM; then we can form a view as to whether
further shortcuts are still required.

> We also have to distinguish Appellations and other Symbolic Objects
> which have multiple symbolic forms, i.e. spelling variants, versions
> etc., from those *being one* symbolic form. The rdfs:value has no
> means to express that. I believe we need yet another property "has
> symbolic content variant". In that case, the URI is necessary, to my
> opinion.
There may be a need for such a property; an analogy would be in SKOS,
which has skos:prefLabel (one per language) and skos:altLabel.  However,
I wonder if there is value in being able to express, in an open world
situation, that one symbolic form is the "right" one and the others are
variants.  I would welcome some concrete examples to inform our discussion.

>From your explanations, I am getting a mental picture of an Appellation
which has been the subject of much study, where you want to record, in a
condensed way, all the possible forms which that Appellation might
take.  For example, the sort of entry you might find in an encyclopaedia
or a biographical authority.  I think that a more typical scenario might
be where the 'same' name (e.g. the name of a known individual) occurs in
a number of sources, but varies between them.

Also, I don't see how introducing a URL helps with this problem.  If you
have an Appellation node in your graph, there are various statements
which you can make about it.  If instead you invent a URL to represent
that Appellation, you are in exactly the same situation as before, in
terms of the statements you can make.  In fact, you have taken one step
backwards, because you now have to begin by declaring explicitly that
this node represents an Appellation: <myURL> rdf:type crm:P41_Appellation.

> I think the polymorphism we describe here, well studied in
> object-oriented languages, is in the nature of Appellations. The
> problem for me is, that the the respective KR models have NOT THOUGHT
> of the case that such polymorphisms can occurr. Nevertheless, RDFS is
> tolerant enough to accept the Superproperty statement, but not to
> create a class which is either URI or *inline expanded* object.
>
> This polymorphism occurs EXCLUSIVELY for Symbolic Objects with symbol
> sets a certain machine supports. Another reason not to use rdfs:value,
> because it does not give credit to the fact that only Symbolic Objects
> can have such a "value".
I'm afraid you have lost me here. It would be very helpful to me (and
might encourage others to join in the conversation) if you could post
one or two concrete examples of what you mean.

Best wishes,

Richard
>
> I agree that we may over-think the point. As I mentioned, the
> superproperty statement I propose has no other effect than that I can
> get E41's and labels back by querying P1 only.
>  
> Opinions?
>
> Best,
>
> Martin
>
> On 9/12/2018 9:56 AM, Richard Light wrote:
>>
>> On 11/09/2018 20:02, Martin Doerr wrote:
>>> Dear All,
>>>
>>> Firstly, apologies, the RDF was wrong, it was intended to be P1 is
>>> superproperty of rdfs:label.
>> I'm not sure that this is something we need to state at all, and I
>> worry that - if it is included in our RDFS Schema - it may bring
>> unwanted side-effects.  Isn't this saying that any instance of
>> rdfs:label is to be treated as an instance of P1?  Bear in mind that
>> CRM data may co-exist in triple stores in company with other RDF
>> data, which may well use rdfs:label for its own purposes.  This
>> assertion that 'all rdfs:labels are P1 relationships' would then be
>> applied to this other data as well.  This might well result in
>> incorrect/spurious results when SPARQL queries are applied to the data.
>>
>> In general, I suggest that we are ok to define sub-classes/properties
>> of standard RDFS types, but we shouldn't define
>> super-classes/properties of them.  (I would welcome comments on the
>> validity of this suggestion from someone who understands RDF better
>> than me.)
>>
>>> Semantically, the range of rdfs:label, when used, is ontologically
>>> an Appellation in the sense of the CRM.
>> Agreed (see my reply from yesterday).  The conclusion I draw from
>> this is that we can validly say:
>>
>> E1 rdfs:label "string value" is a shortcut for the path 'E1 CRM
>> Entity' 'P1 is identified by' 'E41 Appellation' ...
>>
>> in exactly the same spirit as the similarly-worded note which we find
>> in the definition of P1 itself. (Obviously, by using this shortcut,
>> we lose the information that this string value is an Appellation, but
>> that's the nature of short-cuts.)
>>
>>> I agree with George, that all RDF nodes should have a human readable
>>> label. They name the thing, even if it is a technical node.
>>> I would find it confusing to say, labels are not to be queried, only
>>> to be read, and the "real" names must have a URI,
>>> regardless weather I have more to say about it.
>>>
>>> I am really not a fan of punning, we definitely forbid it in the CRM.
>>>
>>> The point with Appellations is that some, the simple ones, can
>>> directly be represented in the machine, or be outside. The solution
>>> to assign a URI in all cases, and then a value or label, does not
>>> make the world easier. It is extremely bad performance. We talk here
>>> about implementation, not about ontology.
>>> You get simply a useless explosion of the graph for a purpose of
>>> theoretic purity.
>> Agreed. What we need to do is to propose a simple way of expressing
>> simple Appellations in RDF.  That is why my shortcut definition above
>> ends with '...': I don't think we have yet decided how to do this.
>>
>> I've just been looking over the draft document we are trying to
>> write, and it currently says that a fully-worked-out path will use
>> 'P3 has note -> E62 string' to express the value of an E41
>> Appellation.  This (i.e. the suggestion to use P3) comes from the
>> definition of the superclass E90 Symbolic Object.  A comment in our
>> draft RDF document questions whether this is sufficiently precise,
>> since P3 is simply "a container for all informal descriptions about
>> an object that have not been expressed in terms of CRM constructs". 
>> I suggest that we need either to use rdfs:value to hold the string
>> value, or (better) to define a CRM-specific subproperty of rdfs:value
>> and use that.  (This subproperty could be part of the published CRM,
>> or it could just form part of the 'RDF implementation' guidelines.) 
>> I don't think that we should use rdfs:label here.
>>
>> I don't think we should concern ourselves with URLs in our RDF
>> guidance document.  Any implementer of our RDF solutions can choose
>> to assign a URL to represent any node in the structure, but it won't
>> change the logic of the resulting RDF, or how it responds to SPARQL
>> queries.
>>
>>>
>>> Those claiming confusing should be more precise. Has someone looked
>>> at query benchmarks? Has someone looked at graphical representations
>>> of RDF graphs. Do they really look better?
>>>
>>> So either we either ignore the issue, and write queries that collect
>>> names either via P1, URI and a value/label, or via a label, because
>>> this is where names appear in RDF, we make no punning, but our
>>> queries implement exactly this meaning. So, we are not better, but
>>> do as if we wouldn't know.
>>>
>>> Or, we describe the fact by punning, have one superproperty for all
>>> cases, which we can query, and stop thereby the discussion if labels
>>> are allowed or not, and how they relate to appellations. The punning
>>> comes in, because the range of the superproperty must comprise the
>>> ranges of the subproperties. We can play a bit more, make the
>>> punning with a superproperty of P1, and have both P1 and rdfs:label
>>> subproperties of it, if this is preferred.
>>> The solution I describe is just a logical representation of the
>>> situation, not creating a different situation. It just says that
>>> names can be complex objects or simple literals.
>> As I said yesterday, I don't see how any punning strategy can make
>> differently-structured RDF equivalent for the purposes of querying.
>> Therefore, I think we will have to accept that if we allow more than
>> one way of representing a given statement in CRM RDF, we will have to
>> construct queries which look explicitly for each of the possible
>> patterns.
>>
>>> The problem is, that the RDF literals do have meaning beyond being
>>> symbol sequences.
>> Insofar as they have such meaning, I would argue that we define it
>> (i.e. that meaning) by the CRM context in which we place the
>> string/literal value.  I think there is a danger that we could
>> over-think this problem.
>>
>> Richard
>>>
>>> The punning does not introduce the problem. With or without, the
>>> queries have to cope with names in either form.
>>> This holds similarly for space primitives and large geometry files,
>>> for short texts and equivalent files etc.
>>>
>>> Opinions?
>>>
>>> Best
>>>
>>> Martin
>>>
>>>
>>
>> -- 
>> *Richard Light*
>>
>>
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>
>
> -- 
> --------------------------------------------------------------
>  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)   |
>                                                              |
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>                 GR70013 Heraklion,Crete,Greece               |
>                                                              |
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-- 
*Richard Light*
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