Re: Interpretation of Relations

Jonathan Leffler wrote:
> Joe Thurbon wrote:

>> I'm very new to this databases game, and am not even sure I'm using 
>> the terminology in the right way. I'd like some feedback as to whether 
>> I'm even in the right ballpark. Most of my understanding of the 
>> terminology comes from reading this group, and the definitions on 
>> Wikipedia.
>>
>> I've been wrestling with the correct interpretation of a relation. I'm 
>> currently working under the assumption that a relation comprises both 
>> a Type (or header) and a Body (or values).
>>
>> I'm going to start small.
>>
>> Consider modelling a situation in which there are people, and they 
>> have eye colour. I'm going to define some very small domains, so that 
>> I can enumerate the facts that I believe a given relation represents. 
>> I'm sorry if the notation is non-standard, but here it is.
>>
>> Domain D_People = {Joe}
>> Domain D_Hair   = {Red, Blond}

Yep. That was intentional. The nub of my question is what happens when you apply the closed world assumption. The bigger the domains, the more implicit negative statements I'd have to enumerate. I agree that the domain is extremely simple, but the purpose is not to actually do any modelling, but rather to examine how the model, once chosen, is interpreted.

>
> Similarly, your domain D_Hair says that the only possible hair colours
> of interest, ever, will be Red and Blond. No-one who has black, white,
> grey, brown, or purple-with-pink-stripes hair will be of interest to
> this database (or, if they are, they'll have to be treated as either red
> or blond or both - or neither?).
>
> So, I think you've over-minimized your domains. Einstein said "Make
> everything as simple as possible, but no simpler".
>

I was probably unclear in my original post, and hopefully I've explained that above. If you don't mind running with the example as written, I'd appreciate hearing any further comments.

Cheers,
Joe Received on Fri Jan 19 2007 - 05:22:35 CET