OWL ontology for unit
Edward.J.Shaya.1 at gsfc.nasa.gov
Fri Aug 29 10:48:47 PDT 2003
I know a lot of NVOers are getting ready to leave for the NVO
meeting so I will be brief. OWL ontology (based on DAML) became a
candidate recommendation at the W3C. This means it is one step from a
recommendation (the highest level).
It looks to us like a good way to model or fully describe VO objects
at a high level. There are supposedly tools to convert to UML and
thence to Schema or code.
As an example, I used the Protege Ontology Builder (
http://protege.stanford.edu/ ) and the OWL pluggin (
http://protege.stanford.edu/plugins/owl/ ) to create an ontology for
describing the various physical units in such a way that they can be
decomposed to baseUnits in SI (gram, meter, second, kelvin, etc).
Protege lets one output OWL/RDF files and also a HTML documentation
of the ontology. Our Unit_Ontology is at (
http://nvo.gsfc.nasa.gov/unit/ontology/ ) and you can get the RDF from
The baseUnits carry dimensional information so one can do
dimensional analysis on derivedUnits. The instances of units and
baseUnits are then terms that one would want to then transfer to an XML
schema, the other objects like PowerOf and InverseOf are just for the
purposes of constucting units.
This also points to a mechanism whereby new units can be defined in
a metadata document and just plug into the system as if it were
This all should prove really useful if we get to the stage where we
want to automatically merge columns of
data or quantity objects and we need an automated way to check if the
two streams of data have the same
physical units and then, if they are, determine what is the constant
factor between them.
More information about the dm