Hi Jonathan,

Presumably you are referring to the Units Ontology and not ontologies in general? The Units Ontology appears to be mainly a controlled vocabulary with no formal definition of relationships between units (and IMHO, in need of some work, as e.g. " microgram per kilogram per day" is not dimensionless).

An ontology can be used to define classes and properties to allow for units conversion and to provide a mechanism for user defined units; I've created such an ontology as proof-of-concept; next is Python code to map RDF descriptions into CellML Canonical Unit Representations.

I agree 100% to only having a single way of specifying and defining units. How about standard URIs backed by ReSTful web services that return both RDF descriptions (from an ontology) and UnitsML (and for that matter, [CellML, SBML, ...]) descriptions? Behind the scenes there would a single "master" definition with mappings to different representations. On the metadata side I envisage a reasoning system to resolve "owl:sameAs" and similar equivalences. A web service could also be used as a source of definitions for units checking and conversion libraries.


Best regards,
Dave


On 28/09/11 10:41 PM, Jonathan Cooper wrote:
Hi Bernard,

I have thought about this a little. The biggest problem with using an ontology is that there doesn't seem to be any possibility of a mechanism for allowing user-defined units. The units ontology at present also doesn't appear to contain enough information to perform units conversions.

It would certainly be beneficial to have a single units language across all COMBINE standards. Given that the SBML world has considered CellML's units to be too complicated, I'm not sure what they'd think of UnitsML! But producing our own version of such a standard does seem rather foolish. I wonder if there's scope for a 'lite' version of UnitsML that could be incorporated?

From the very brief look I had, UnitsML does seem pretty comprehensive. I wasn't too enamoured of their approach to defining conversions though - you ought in most cases to be able to deduce appropriate conversions from the units definition, so it may be that they're lacking detail there.

Best wishes,
Jonathan

On 28/09/11 10:34, Bernard de Bono wrote:
Hi,

Is, alternatively, the use of an ontology for units also a consideration? Terms from such an ontology could be applied to the annotation of semantic metadata associated both with (i) model variables, as well as (ii) related datasets.

Thoughts most welcome.

All the best,

Bernard


On 28 September 2011 09:49, Steve McKeever <steve.mckee...@cs.ox.ac.uk <mailto:steve.mckee...@cs.ox.ac.uk>> wrote:

    Hi,
    Only had a quick read through but it looks good, perhaps a bit
    too comprehensive for CellML and FieldML. Hard to tell if it will
    become *the* standard for units though.
    Steve

    On 27 Sep 2011, at 01:04, David Brooks wrote:

    Hi,

    I've come across the Units Markup Language (UnitsML,
    http://unitsml.nist.gov/), which is a project of the National
    Institute of Standards and Technology for encoding scientific
    units of measure in XML. It is currently being standardised by
    OASIS (the Working Draft is at
    
http://www.oasis-open.org/committees/download.php/42538/UnitsML-Guide-v1.0-wd01.pdf).

    Should UnitsML be embedded in a future version of CellML? In
    FieldML? To become the preferred way to specify units in the
    various MLs??


    Regards,
    Dave
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