# RE: (Round 2) Proposed Extensions to OWL

From: Roger L. Costello <costello@mitre.org>
Date: Wed, 02 Jul 2003 15:30:35 -0400
Message-ID: <3F0332DB.E86ECFD@mitre.org>

CC: "Costello,Roger L." <costello@mitre.org>, jon@spin.ie, tpassin@comcast.net
```
Okay, let's review to see where we stand.  Here are two descriptions of
the Yangtze River which use the form that we are currently proposing:

Document #1 shows the length in kilometers:

<River rdf:ID="Yangtze">
<length>
<Length>
<measurement>
<LengthInKilometers>
<number>6300</number>
</LengthInKilometers>
</measurement>
</Length>
</length>
</River>

Document #2 shows the length in miles:

<River rdf:ID="Yangtze">
<length>
<Length>
<measurement>
<LengthInMiles>
<number>3914</number>
</LengthInMiles>
</measurement>
</Length>
</length>
</River>

LengthInKilometers and LengthInMiles are subclasses of LengthMeasure:

LengthMeasure
|       |
--------       ---------
|                       |
LengthInKilometers     LengthInMiles

The above two documents are related.  Namely, the value of their length
property represent the same length.

What should we expect an ontology to define?  I like the way Tom lays
out fundamental facts, so here's my attempt at laying out the
fundamental facts:

1. A River has only one length, i.e., the cardinality of length equals
one.  OWL can express this.

2. The length can be "modeled" in many different ways.  A model of the
length is the result of a transformation of the physical object into a
form that is easier for humans and machines to deal with, i.e.,

length(Yangtze River) = <Length>
^         ^              <measurement>
|         |                 <LengthInKilometers>
|         |                    <number>6300</number>
|         |                 </LengthInKilometers>
|         |              </measurement>
|         |           </Length>
|         |                ^
|         |                |
transformation |                |
physical object      |
model

There are many different ways to model the length of the Yangtze River.
For example, here's another model of the length of the Yangtze River:

<Length>
<measurement>
<LengthInMiles>
<number>3914</number>
</LengthInMiles>
</measurement>
</Length>

The above two models are related by a conversion factor.

Question: are all models of the length of the Yangtze River related by a
conversion factor?

Question: what is the role of OWL with respect to these models?  Should
an OWL document be responsible for stating the conversion factor among
models?

Jon Hanna made an interesting suggestion last week:

"... (Separating the conversion factors from OWL) seems analogous to the
way several successful internet technologies work, e.g. HTML has a way
of saying 'image goes here' but relies on other technologies to actually
encode, transmit and render the image. So maybe OWL could benefit from
being able to say 'conversion goes here'".

Perhaps the role of an OWL document in describing the relationships
between the length models may be something as simple as this:

<owl:Class rdf:ID="LengthInKilometers">
<owlx:convertibleModels>
<owl:Class>
<owl:unionOf rdf:parseType="Collection">
</owl:unionOf>
</owl:Class>
</owlx:convertibleModels>
</owl:Class>

That is, an OWL document simply identifies which length models are
convertible. An application must "out-of-band" locate the conversion
routines.