[Crm-sig] Using multiple instantiation

Martin Doerr martin at ics.forth.gr
Thu Dec 6 00:00:21 EET 2018


This was a proposal by Robert :-). It may be useful for implementers not 
used to semantic technologies.

What do other people think?

On 12/5/2018 6:54 PM, Richard Light wrote:
>
> Martin,
>
> Please explain why you think that this text is needed in the RDF 
> implementation guidelines. To me, it seems quite generic, and doesn't 
> offer specific guidance as to what implementors should do about the 
> issue that their existing systems may be incapable of expressing 
> certain RDF features. I think it would actually detract from the 
> usefulness of the document, because it would confuse and puzzle the 
> typical reader.  [Maybe we need to stop and think about who the 
> 'typical reader' would be, and what they would want from this document.]
>
> Richard
>
> On 05/12/2018 16:05, Martin Doerr wrote:
>>
>> Dear All,
>>
>> I propose this paragraph to be added to the implementation guidelines 
>> for RDFS:
>>
>> "*About implementing multiple Instantiation*
>>
>> Knowledge representation models and more generally semantic networks 
>> differ fundamentally in one aspect from data structures, such as XML, 
>> Relational database schemata and data structures in all programming 
>> languages, including the object-oriented one:
>>
>> ·Knowledge representation starts with an item in the real world 
>> regardless its nature, assigns an identifier to it in order to be 
>> able to make assertions about it, and then accumulates statements 
>> (assertions, propositions) about it.
>>
>> ·Data structures start with a set of templates, a set of foreseen 
>> kinds of statements dedicated to a particular category each (class, 
>> entity), to be filled in by a user.
>>
>> Consequently, knowledge representation may assign multiple classes to 
>> a given identifier without any problem. The associated processing 
>> software will then allow for asserting for this identifier all 
>> properties applicable to each assigned class. This process is called 
>> “multiple instantiation. For instance, the “weapon” with all its 
>> characteristics may also be a “ceremonial object”.
>>
>> A system based on data structures must create a different instance of 
>> the respective templates for each class an item belongs to. It may 
>> later the link the different instances describing aspects of the same 
>> thing, in order to simulate the mechanism. In particular the very 
>> successful “encapsulation principle” of object-oriented programming 
>> languages requires dedicated data structures and constitutes a 
>> fundamental mismatch with the Open-World modeling of semantic 
>> relationships (see, for instance Schnase 1993). Fundamental to 
>> semantic data integration are also superproperties, which are not 
>> provided by data structures either.
>>
>> The CRM as ontology relies heavily on multiple instantiation: Classes 
>> that use to co-occur on things simultaneously “incidentally”, without 
>> being associated with properties only applicable to the combination 
>> of such classes, are not modelled individually as subclasses of 
>> multiple parent classes. The latter would be called “multiple IsA”. 
>> To avoid multiple IsA in such cases is an important normalization 
>> principle to keep the ontology very compact and unambiguous.
>>
>> Most implementations on top of RDF still use RDF as if it were a 
>> fixed schema and repeat in the UI code all the schema. Therefore, the 
>> promise of RDF and other semantic models to be able to accommodate 
>> dynamically new properties often does not work. It is still as if 
>> they were using Relational systems. Generic XML editors do adapt 
>> already to the schema, but usually the rendering paradigms they 
>> employ, without additional parameters, are too poor for good UI code. 
>> One can however write code that reads the RDF schema used at run-time 
>> and that extends data entry and display by the actual properties 
>> found. This functionality is foreseen by SPARQL, but most programmers 
>> still do not appreciate the utility of querying the schema. Even if 
>> fixed templates are used, the data entry system should foresee the 
>> same thing to be described by multiple templates, relatively freely 
>> selectable by the user.
>>
>> In the specification modules of mapping software used to transform 
>> data into a CRM-compatible form, care must be taken to foresee and 
>> allow the user to combine RDF classes systematically. It may be 
>> useful to develop tools for specific guidance that show users how a 
>> valid path from a given domain class to a certain range class can be 
>> created by using multiple instantiation (and, by the way, also by 
>> using subclasses of the domain class), such as combining /E41 
>> Appellation/ with /E33 Linguistic Object/ in order to reach /E56 
>> Language/ via /P72 has language./
>>
>> In a local system, another workaround for multiple instantiation can 
>> be the creation of classes that replace all candidate cases for 
>> multiple instantiation by subclasses using multiple IsA. For good 
>> reasons, the compatibility with the CRM is defined at the 
>> import/export/query level and not at the system internals. Therefore, 
>> such internal workarounds do not affect the interoperability: Whereas 
>> the query compatibility of this solution with the standard is 
>> immediate, the respective import/export system simply needs to make 
>> the trivial replacements of the respective class combinations with 
>> their multiple IsA counterparts and vice-versa.
>>
>> So, partially, problems with multiple instantiation are a question of 
>> programming practice. On the other side, it is also a question of 
>> user training and extended good practice. Users may provide feedback 
>> about frequent cases where multiple instantiation is used, in order 
>> to guide users to these modelling cases. These could systematically 
>> be entered into the CRM RDF implementation, without requiring the CRM 
>> standard itself to repeat them."
>>
>> John L. Schnase, (1993). "Semantic Data Modelling of Hypermedia 
>> Associations", in: ACM Transactions on Information Systems, 
>> Vol.11,No.1, January 1993, p 45.
>>
>> Comments welcome!
>>
>> Best,
>>
>>
>> Martin
>>
>> -- 
>> ------------------------------------
>>   Dr. Martin Doerr
>>                
>>   Honorary Head of the
>>   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
>>   
>>   Vox:+30(2810)391625
>>   Email:martin at ics.forth.gr   
>>   Web-site:http://www.ics.forth.gr/isl  
>>
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> -- 
> *Richard Light*
>
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-- 
------------------------------------
  Dr. Martin Doerr
               
  Honorary Head of the
  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
  
  Vox:+30(2810)391625
  Email: martin at ics.forth.gr
  Web-site: http://www.ics.forth.gr/isl

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