> > > I could store the department and business attributes with the >> > employee, but without proper constraints the referenced department >> > could conceivably not correspond to the referenced business. Or I >> > could ensure that all businesses have at least one department, >> > defaulting to the business when the business has no department, but >> > then I'd be storing duplicate data. The other alternative I've come up >> > with is an exclusive constraint where the employee instance can only >> > reference a department or a business, but not both. >> > >> > None of these solutions seems ideal, although the exclusivity solution >> > seems like it would work the best, and I have had to create >> > exclusivity constraints before. So, am I missing a more obvious >> > solution, or am I even on track here? >> >> I’ve found this « Universal Person and Organization Data Model » very >> useful to understand complex questions like that: >> http://www.tdan.com/view-articles/5014 >> >> Hope this helps, >> François Beausoleil >> >> > Thanks François. This is pretty generic stuff, but my first reading has > got me thinking that I should at least pick up some ideas from it. I will > give it a go. And I've got a new web site that I've now known about before, > so thanks for that as well. > > Regards, > Nelson > > > I strongly suggest you read the writings of Joe Celko, he has been > addressing this kind of problem for decades. Ultimately, it is very > important not to confuse behaviour with entities (yes employment is > behavioural) > > Cheers >
Thanks Robin. Ironically enough, our little local library has three books by Joe Celko, so looks like I may have a weekend of reading ahead of me. Nelson
