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Hi Folks,
Below I outline a strategy for realizing the full flexibility of XML
through the use of OWL ontologies. Comments welcome. /Roger
Prior to outlining the strategy I need to define some terminology that I
will use.
Terminology - Logical Design
An OWL ontology defines the fundamental relationships of
your data. That is, an OWL ontology defines a "logical
design".
Example of fundamental relationships for camera data:
- SLR is a type of Camera
- f-stop is synonymous with aperture
- focal-length is synonymous with lens size
Terminology - Physical Expression
An instance document is a "physical expression" of the logical design.
For a given logical design there are many possible physical
expressions.
Example of a physical expression for camera data:
<SLR rdf:ID="Olympus-OM-10">
<viewFinder>twin mirror</viewFinder>
<optics>
<Lens>
<focal-length>75-300mm zoom</focal-length>
<f-stop>4.0-4.5</f-stop>
</Lens>
</optics>
<shutter-speed>1/2000 sec. to 10 sec.</shutter-speed>
</SLR>
Here's another physical expression:
<Camera rdf:ID="Olympus-OM-10">
<viewFinder>twin mirror</viewFinder>
<optics>
<Lens>
<size>300mm zoom</size>
<aperture>4.5</aperture>
</Lens>
</optics>
<shutter-speed>1/2000 sec. to 10 sec.</shutter-speed>
</Camera>
Note that the first physical expression uses this terminology:
SLR, f-stop, focal-length
While the second physical expression uses this terminology:
camera, aperture, (lens) size
These represent two (of many) physical expressions of the
same logical model.
Strategy Objective
- Maximize diversity of physical expression.
- Allow (and encourage!) diversity of physical expression.
- that is, create instance documents in a style
which meets your needs/desires.
- Liberate from requiring every application to use the
same terminology (i.e., the same tag names).
- Truly realize XML's flexibility.
Strategy
The strategy is quite simple: all parties participating in
an exchange of data can compose any physical expression, provided
the physical expression does not violate the fundamental data
relationships defined in the logical design.
Thus, one person can create a camera document like the first one
shown above. Another person can compose a camera document like
the second one shown above. Using the unifying logical design
(i.e., the OWL ontology) the two people can interoperate seamlessly.
Concept of Operation
Here's the concept of operation: Let's take the camera example.
Suppose that my application receives a physical expression (i.e., an
instance document) from a trading partner. Further, suppose that my
application is coded to understand this vocabulary:
camera, aperture, (lens) size
My trading partner has taken advantage of XML's flexibility and has
elected to use this terminology:
SLR, f-stop, focal-length
As my application parses the XML document that it received from the
trading partner it encounters <SLR>. It doesn't "understand" SLR so it
"consults" the Camera ontology:
"What do you know about SLR?"
The ontology returns:
"SLR is a type of Camera."
This knowledge provides the link for my application to understand the
relationship between something it doesn't know (SLR) to something it
does know (Camera).
My application continues parsing...
It encounters <f-stop>. Again, my application was not coded to
understand f-stop, so it consults the Camera ontology:
"What do you know about f-stop?"
The ontology returns:
"f-stop is synonymous with aperture."
Once again, this knowledge serves to bridge the terminology gap.
Ditto for focal-length...
Summary
Interoperability despite terminology differences! There can be many
different physical expressions (i.e., instance documents can be in
various forms). The flexibility of XML is being realized!
When an application processes a physical expression (i.e., an instance
document) it "consults" an ontology for vocabulary it is not
knowledgeable about.
Performance
One point of using an ontology is that it allows for near linear
semantic integration rather than n**2 integration. Each
application/database maps to the "lingua franca" of the ontology, rather
than to each other.
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