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:[email protected]
Web-site:http://www.ics.forth.gr/isl
_______________________________________________
Crm-sig mailing list
[email protected]
http://lists.ics.forth.gr/mailman/listinfo/crm-sig
--
*Richard Light*
_______________________________________________
Crm-sig mailing list
[email protected]
http://lists.ics.forth.gr/mailman/listinfo/crm-sig
--
------------------------------------
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: [email protected]
Web-site: http://www.ics.forth.gr/isl
