help with dated entailments ... (for POWDER)

(originally sent to OWL WG; where Bijan replied, and I will follow up to 
his message here)

........................

-----------
In my analysis of what is going in POWDER I have now written

http://www.w3.org/2007/OWL/wiki/POWDER

I have a question.

POWDER includes two properties wdr:validFrom and wdr:validUntil.

Inbetween these dates then an example like:


http://www.w3.org/2007/OWL/wiki/POWDER#Example

should 'entail'

http://www.w3.org/2007/OWL/wiki/POWDER#The_subclass_relationship

===

Outside these dates the 'entailment' is not known to hold.

========

Clearly a full formal treatment of time is well outside the scope of
what will be included in the POWDER specification.

So how do I hack it?

Or perhaps more positively, how do I express pragmatically the
relationships.

I have to define a semantic extension to RDF, so I have quite a lot of
wiggle room, but need to use it cautiously.

=======
I'll try writing a straw man and adding it to the page.

Might take an hour or two.

=====


Note for the DL people - I need to also articulate how my approach
relates to OWL DL.

Jeremy