On Sun, 3 Feb 2008, Jeff Davis wrote:
I think what he means by "bitemporal" is what CJ Date, et al., refer to as "fully temporal" (as opposed to semi-temporal), that is, dealing with time intervals rather than time points.
I think fully temporal is a step of complexity above how some people use bitemporal but this terminology is slippery.
Bitemporal databases are ones where every transaction gets two timestamps: one at transaction commit and a second that encodes what time that transaction is valid as of. A classic example uses a bitemporal employee promotion table to track the company org chart. With the "valid as of" timestamp in there, if you structure the query right you can generate a report as of any particular point in time and find out what the structure of the organization was at that point. There's all sorts of applications where being able to track the state not just of the current table but of where it was at a previous/future time can be handy, and bitemporal approaches can be easier to handle than something like a history table.
While there's useful syntax to add, I believe one challenge of bitemporal databases from the -hackers perspective involves how to accelerate the typical queries people run. Here's some research that looks into things like how to index the data usefully, and that gives more references into the bitemp literature: http://www.cs.ucr.edu/~tsotras/temporal.html
I would suggest a book called "Temporal Data and the Relational Model", by C. J. Date, Hugh Darwen and Nikos A Lorentzos to anyone who's interested in temporal issues.
I think you need to be familiar with the work set down in both that one and the Snodgrass/Jensen "Developing Time-Oriented Database Applications in SQL" before you can even start do anything that's actually new in this area. Bitemporal tables show up early in that book (P44 of the PDF http://www.cs.arizona.edu/people/rts/tdbbook.pdf ) The way they use them, the valid and transaction times are both intervals rather than points, which I think makes the implementation there look more like Date's fully-temporal tables.
-- * Greg Smith [EMAIL PROTECTED] http://www.gregsmith.com Baltimore, MD ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
