Raw

There's a good blogosphere thread going on around temporal labelling and RDF ("timestamp your triples!"), see posts from John Barstow, Seth Ladd and Jeen Broekstra.

I've nothing original to add, but my opinion is pretty close to what Chimezie Ogbuji says:

I think the problem is more a modeling issue (and having the foresight to determine how you accomodate the change of data over time) than a shortcoming of the framework.

Temporal stuff is notoriously tricky in general, but I think RDF/OWL has enough capability for providing a useful representation the vast majority of cases, even if rules may be needed to reason over the stuff.



Over on the semantic-web@w3.org, Sandro Hawke made a point about provenance that I believe applies equally well to temporal labelling :

Publishing statements as triples makes sense. Whatever you want your web page to say, just put those statements on the page. You shouldn't have to put on the page a statement that those statements are on the page and are true. Say "The sky is blue", not "I am now telling you that the sky is blue."



For reasoning about statements, yes, of course use quads. When I harvest RDF data, of course I keep track of what web pages said what. But I don't usually need to re-publish that harvester data; that's like my web browser publishing my browsing history along with the browser cache. There are applications where that's useful, sure, but it's hardly the main way data moves around the web.

If the temporal side is really important for the application then even 5-tuples can be used locally, but in most cases I suspect an implicit named graph approach (this page of triples was last modified 2006-03-20) and/or reification will be adequate.



Timestamps run all through the world of content management. Probably the trickiest bit of expressing Atom in OWL relates to changes over time - a core feature of Atom - as Henry Story will confirm (Henry's solution is to use CIFPs). This isn't just an issue for RDF, argument over how to do dates in Atom itself generated almost as much debate as argument over the name...

For similar motivations, one of the targets of Reto Bachmann-Gmuer's work around diff and patch is to try and tackle the general problem of versioning in RDF.

@en