OWL ontology for unit

[Ed Shaya]

Hi,
    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 
there.
    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 
standartd units.
    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.
 
Ed