[Crm-sig] Using multiple instantiation
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:
> 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.]
> 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!
>> 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
>> Email:martin at ics.forth.gr
>> Crm-sig mailing list
>> Crm-sig at ics.forth.gr
> *Richard Light*
> Crm-sig mailing list
> Crm-sig at ics.forth.gr
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,
Email: martin at ics.forth.gr
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