[crm-sig] Uniqueness of property names in the CRM.

martin martin at ics.forth.gr
Wed Oct 9 13:57:42 EEST 2002


Dear All,

I had the following question about the CRM, I think it is a good FAQ.
Please let me know, if you disagree with my explanations:

 >I am curious about the lack of uniqueness in the naming of CRM properties.



 >(1) You have a single ID for each property, covering both directions, eg P9 = consists of (forms part of). In RDD we assign IDs to both directions, as they are semantically distinct.


This is a philosophical topic. For us, both directions belong to the same, directed
property. We do not accept models for the scope of the CRM, that use one-way links.
For us, if there is a link, it can always be read in two directions, normally like
active and passive voice. We can discuss more about that. Not all models regard both
directions as semantically different. E.g. UML assigns two names, as we do.




 >(2) Property names are also not unique (eg "consists of" for P5, P9, P45 and P88).


The property is unique by the number, not by the name. Names are mnemonics,
not meant to convey meaning but to remind the meaning. The CRM is intended to
be international, not English. In a translation, mnemonics are exchanged,
numbers persist.





 >There does not seem to be any strict consistency in the definitions of properties with the same name, or of the pairings of names: eg
 >
 >    P5    Condition State    consists of (forms part of)    Condition State
 >
 >    P9    Period                consists of (forms part of)       Period
 >
 >    P45  Physical Stuff        consists of (is incorporated in)    Material
 >
 >    P46  Physical Stuff        is composed of (forms part of)    Physical Stuff
 >
 > so I assume there are no underlying abstract properties or verbs which unite them?


Underlying abstract properties are given explicitly by "subproperty of" statements,
and are not linguistically implied. In cases of pure restriction, as the
"identified by" series, the same name is used deliberately. The mnemonic is always
chosen to give a better reading in context. P5, P9 and P45 never co-occurr, because the
entities are disjoint.

The mnemonics work well to replace properties in data by quasi-
natural language. This is very beneficial to convey the model to non-computer experts.
We are more interested in how an instance looks like under the CRM schema, than how the
CRM schema looks like as a total. This is also due to the fact, that the CRM is not designed
as data entry tool, where users would need to select properties,(and may be confused by
multiple occurrence of the same name) but for transformation of
data under local data structures into a common form.

We deliberately did not assume a common "part-of" theory. There are too many different
axioms, even for material objects, so that "part-of" seems rather to be on a meta-meta-level.
Particularly, a common part-of of disjunct concepts would introduce "unintended models".
Periods, e.g. can't consist of Physical Stuff !





 >This creates some difficulties in mapping to other schemas, as it means there is no unique single name, for example, for "consists of" as a property linking Physical Stuff and Material. I can see 
 >that this is manageable when using CRM as a reference model, but I wonder if you have considered the implications for mapping?


We do have. Map to the identifier. Use the names as representation labels.



 >I have been doing some test mappings, and I have simply used (for example) "P9a" and "P9b" to distinguish the directions of properties. The non-unique textual names do not then cause an >absolute 
problem, although it is confusing to have elements with identical headwords.


If you read our RDFS version, you will see the same. Due to an ugly assymetry
in RDF use of properties, we are forced to declare forward and backward
properties as distinct, even though in RDFS they are symmetric.

We propose: P9F, P9B for those models, that cannot deal with bidirectional
properties. That allows to recover the common meaning at any useful time.




 >Have I understood this correctly, or missed something? Can you explain your thinking on this?


To make the point more clear: If Martin "is son of" Wolfgang, Wolfgang "has son" Martin.
This is a coimplication. Hence, there are not two independent concepts. Do you
have other concepts in mind?

Please let me know, if this makes sense, or if I have missed something.

======================================

BTW, the latest version of the CRM is now available as RDFS. Please test.
(http://cidoc.ics.forth.gr/docs/xml_to_rdfs/CIDOC_v3.3.2.rdfs).
It is machine generated, so I hope it is free of spelling errors.

best,

Martin

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