On Tue, 23 Jul 2002, Chris Croome wrote:
> I realise that this question has been asked before [1], but since it is
> a problem that is going to arise again and again...
>
> How should one represent the duration of a multi-media file in seconds
> _and_ the size of the file in bytes using the Dublin Core Extent
> qualifier of Format?
>
> Extent is defined as:
>
> The size or duration of the resource. [2]
>
> Does the 'or' mean that a file can only have a duration or a size?
No, it means that you can repeat dcterms:extent to carry both kinds of
information
<dcterms:extent>123 seconds</dcterms:extent>
<dcterms:extent>123 bytes</dcterms:extent>
> If we were modeling Heisenberg's uncertainty principle [3] then this
> kind of thing might make sense -- if the position is specified then the
> momentum cannot be, however we are not and it seems reasonable to me
> that there are times when, for example, the file size (bytes) and
> duration (seconds) of an audio file are aspects of the file that _both_
> need to be described.
>
> I'd like to be able to do something like this:
>
> <dcterms:extent>
> <foo:seconds>123</foo:seconds>
> <foo:bytes>123</foo:bytes>
> </dcterms:extent>
>
> But with out having to invent my own foo namespace.
>
> Anyone got any suggestions?
No real suggestions I'm afraid...
I'm assuming that your XML snippet above is plain XML, rather than
RDF/XML, in which case (as has been discussed on the dc-architecture list)
there are no agreed conventions for how to handle the kind of element
nesting that you are proposing. That's not a reason not to do it within
your closed world - but you should be aware that any external consumers of
your XML may well not understand it.
The DC Format WG, which came up with the dcterms:extent proposal, didn't
reach any conclusions about suitable sub-properties to handle size and
duration. You could invent your own, e.g. foo:duration and foo:filesize
or as you have above, and declare them (in RDFS) as sub-properties of
dcterms:extent. Then your instance metadata would simply contain
<foo:duration>123</foo:duration>
<foo:filesize>123</foo:filesize>
You could look at MPEG-7 ?? A very quick Google search turns up
http://www.metadata.net/harmony/MW2002_paper.pdf
by Jane Hunter which shows MPEG-7 properties called 'FileSize' and
'MediaDuration' (in the urn:mpeg:mpeg7:schema:2001 namespace) but this
isn't my area and I have no idea about the current state of this work or
its implementation in RDF.
Andy
--
Distributed Systems, UKOLN, University of Bath, Bath, BA2 7AY, UK
http://www.ukoln.ac.uk/ukoln/staff/a.powell +44 1225 383933
Resource Discovery Network http://www.rdn.ac.uk/
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