I think you're right about it being an implementation issue, Guy. I
think the confusion arises because, having spent twenty years or more
with 'data model' being an ERM (or similar) diagram produced before
implementing a database design, I don't see how it can be used as
'metadata' or an 'ontology'.
However, I guess if the model is produced using UML and stored as XMI then it could be interrogated.
Is this what the 'data model' people are doing? Specifying a data model for VOs that can also be interrogated as metadata? In which case what standards are being used for the data model format?
I guess this is a useful way of storing structural metadata with some relationship information in the links between 'tables' but I wonder how much and what type of information cannot be stored in this way. And is it important to what we want to do?
I think the biggest potential problem is that it IS structural. An ontology or loosely stored metadata does not mandate how the data itself is stored. An important point when many projects are working towards an interoperable VO but not using or even based on the same implementation. A data model may enforce structures that some people do not want to use.
Hmm, what do others think?
Cheers,
Tony.
> -----Original Message-----
> From: Guy Rixon [mailto:gtr-at-ast.cam.ac.uk]
> Sent: 10 November 2002 16:28
> To: Tony Linde
> Cc: semantics-at-us-vo.org
> Subject: Re: Confused
>
>
> Tony,
>
> perhaps it's an implementation dispute rather than a definition thing?
>
> The IVOA data models are now specified to be expressible
> using UML. That is, they only contain relationships "is a"
> and "has a" (and perhaps "owns" if we distinguish composition
> from aggregation). The ontological content is restricted, so
> much of this modelling can be done with existing tools that
> support OOA.
>
> Conversely, if we use lots of relationships, then we have to
> use specialised tools from recent ontology research; tools
> that look vaporous right now.
>
> I think your definitions are right. I also think that many
> VO folk ignore the ontological theory behind their current
> modelling because it's not necesary to know the thory to use
> the technique.
>
> On Fri, 8 Nov 2002, Tony Linde wrote:
>
> > I've seen comments saying that we should use metadata instead of
> > ontologies, data models instead of ontologies, data models
> instead of
> > metadata etc.
> >
> > So what is the difference? And what do people mean by these terms?
> >
> > For myself:
> >
> > Data is information stored electronically.
> > Metadata is data which describes some other data.
> > Dataset is a collection of data organised by some principle. Data
> > model is an ERM of a dataset which describes its underlying
> > construction.
> >
> > Ontology is all of the terms and semantic relationships
> used in some
> > domain discourse (which may be discovered and stored
> digitally but not
> > necessarily).
> >
> > How about you?
> >
> > Cheers,
> > Tony.
> >
> > __
> > Tony Linde Phone: +44 (0)116 223 1292
> > AstroGrid Project Manager Fax: +44 (0)116 252 3311
> > Dept of Physics & Astronomy Mobile: +44 (0)7753 603356
> > University of Leicester Email: ael-at-star.le.ac.uk
> > Leicester, UK LE1 7RH Web: http://www.astrogrid.org
> >
> >
> >
>
> Guy Rixon gtr-at-ast.cam.ac.uk
> Institute of Astronomy Tel: +44-1223-337542
> Madingley Road, Cambridge, UK, CB3 0HA Fax:
> +44-1223-337523
>
Received on 2002-11-12Z10:26:05