Actually, what would be really nice is if there were just a button I could push that would make all of my data automatically correct. Can that go into 8.3? Thanks, ...Robert -----Original Message----- From: Alvaro Herrera [mailto:alvherre@xxxxxxxxxxxxxxxxx] Sent: Friday, February 23, 2007 9:35 AM To: Alban Hertroys Cc: Robert Haas; David Fetter; pgsql-general@xxxxxxxxxxxxxx Subject: Re: [GENERAL] complex referential integrity constraints Alban Hertroys wrote: > Robert Haas wrote: > > The idea here is that a wolf can attack a sheep, or a wolf can attack > > another wolf, but sheep can't attack anything. I suppose I could list > > each wolf in both the predator and prey tables, but that seems a bit > > duplicative (and causes other problems). > > I'm quite certain a wolf is much more likely to attack a sheep than to > attack another wolf, and even more unlikely to attack for example a > lion. It seems to me that just the fact that it can isn't enough > information. > > It looks like you need "weighted constraints"; there's 0 chance that a > sheep attacks a wolf, but there's >0 chance that a wolf attacks a sheep, > >0 chance it attacks a wolf and >0 chance it attacks a lion. The exact > numbers will vary, and I have absolutely no idea what they would be > like. It probably requires some kind of ranking system that adjusts > according to the known animals and their likelihood to attack eachother. Depending on what you're modelling, even this could be too simple -- for example, while a single wolf is unlikely to attack a lion, a pack of wolves have a lot more probability of doing so. Do you keep packs of wolves in your barn? If so, watch your lions. -- Alvaro Herrera http://www.CommandPrompt.com/ The PostgreSQL Company - Command Prompt, Inc.
