http://dublincore.org/
Dublin Core is used for document properties.  The Dublin Core standard is
used by OpenOffice.org, Abiword and Gnumeric (not sure about Gnumeric
exactly).  
I intend to add it to the Dia file format and use it in various places.  

The first place i intend to add it is in the Sheet files as it will be the
easiest.  
I also plan to add it to the ordinary Dia files and then Add a Properties
Dialog in the (Document) File menu.  
I have some ideas about adding some dublin core to the shape files but that
is a very low priority.  

Currently the sheets contain information similar to this

<!--Dia-Version: 0.90-->
<!--File: C:\Program Files\dia\.dia\sheets\monkey.sheet-->
<!--Date: Sun Nov 24 18:39:53 2002-->
<!--For: horkana-->

which we could very easily turn this infromation into Dublin Core
<dc:creator>Alan Horkan</dc:creator>
<dc:date></dc:date> (date is specified in some specific standardised format

Dublin core does not specify a version tag, for this we might consider
resuing the 'meta' namespace specified by OpenOffice.org but I will look
into it later.  

I have given plenty of thought to this.  
These notes are only to give you a rought idea of what i am on about, I
will add more detail and what should be clear when i have done it.