Update: Since there seems to be some confusion: This blog discusses the Xesam ontology, not the desktop search API!
For a long time now we had two desktop ontologies trying to solve the same problems: the Xesam ontology and NIE (Nepomuk Information Elements) both define classes and properties to describe desktop metadata ranging from id3 tags (artist, title, and so on) to emails and instant messaging. While the latter was developed as part of the Nepomuk project, the Xesam ontology was a by-product of the Xesam desktop search API project on freedesktop.org mainly designed by Evgeny (Phreedom) Egorochkin.
Now although I am obviously biased I cannot say if one was better than the other. What I can say is that NIE was more complete then Xesam. In any case, even during that time both ontologies benefited from each-other. NIE contains ideas from Xesam and the other way around. So both ontologies were already pretty close. All that was left to do was a merger. And that is what happened now. Sort of.
With Nokia pushing Tracker and being very interested in semantic desktop technology, with KDE leaning towards Nepomuk anyway (ok, that is my fault), and with Evgeny, being the lead Xesam ontology developer, wanting this merge to happen sooner than later NIE sort of won. Tracker now uses NIE and Strigi was also ported to NIE recently. Discussions on the xesam mailing list suggest that ther Xesam ontology can be seen as deprecated now. Any advantages it has over NIE should be either merged into NIE or maintained as an extension to NIE.
I think this is a great development. And again this should not be seen as a defeat of Xesam. As I said: many ideas from Xesam already found their way into NIE and others will in the future. Evgeny and Philip Van Hoof (working on Tracker) already created extensions to at least NMO which should be merged soon.
But IMHO we now should make sure that we do not end up with multiple versions of NIE all over the place. Strigi’s source code now contains copies of NIE, kdebase already contains NIE (alongside other ontologies), and I figure that the same is true for Tracker. Thus, to avoid having one ontology installed in different versions and different places from different packages, I suggest that we create a new project which is only concerned with the desktop ontologies. It has already be done with mime types. So why not do the same with ontologies.
The OSCAF foundation, a result from the Nepomuk project, was supposed to maintain these ontologies. However, so far not much has happened. So we created a sourceforge project which could serve as the platform to collaboratively develop these desktop ontologies. The way I see it we could use a subversion repository to develop the ontologies and put the stable versions on the semanticdesktop.org server. In any case I think we need some platform for the ontologies. And just a wiki is not enough.
A short comment on the technical side: In kdebase I maintain the ontologies as a pair of trig source files and desktop files which describe the ontology (name, comment, namespace, path to source file, etc.). Maybe this could be a starting point to get to a common way of storing ontologies for the desktop.