Re: Question on Multiplicity

jason.glumidge_at_gmail.com wrote:
...
> With the above example the predicate I had in mind (although not
> explicitly - probably my first mistake), was:
>
> "There is an animal:<A> with some fur colored <C>"
>
> This may be a bad choice (i'm still not completely clear on this) - is
> the implication that such a predicate constrains my declaration of the
> world to all animals only having one fur-color?
> ...

it might be or it might not be. if you're assuming the RM, it seems to be pretty transparent on the topic of how we should interpret predicates. i'd say the RM doesn't care about 'implications' except the ones it is able to reflect. actually, it doesn't even care about those, it merely reflects them! or should i say, manipulates them in its own limited way. i'd even go so far as to say that it can't really express them, at least in the sense that we understand the word - that's why i said reflect rather than express!

(this is just a hobby for me so i should warn you that i suspect some serious 'data modellers' i've known might say i'm wrong in the above and i do get lots of things wrong, most recently saying that transitive closure was possible without recursion!)

to somebody else, the above predicate could mean 'this animal is NEVER this colour', etc., etc. so you'd have to come to some agreement with them before you let them share your database! as you hinted (if i remember correctly) earlier, the choice of key would introduce a constraint but maybe not the one you want.

you seem to be talking about two different things, for example, all possible colours of a particular species and the colour of one individual. two different subjects usually means several relations.

always helps me to imagine the queries i want to make and the answers i'd expect to get.

p Received on Wed Oct 26 2005 - 21:27:15 CEST