Re: MV Keys (was: Key attributes with list values)

"JOG" <jog_at_cs.nott.ac.uk> wrote:

>Marshall Spight wrote:
>> David Cressey wrote:
>> > "mAsterdam" <mAsterdam_at_vrijdag.org> wrote
>> I've always maintained that any question about whether a collection

>> is ordered or not (such as a collection of pizza toppings) is a
>> question of domain modelling. The question of whether
>> onion, mushroom = mushroom, onion is exactly the question
>> of whether this particular collection is considered ordered
>> in this particular domain. To answer that, we need a
>> domain expert.

>Yes! This point is crucial and why (dawn ;) one should desperately
>avoid the conceptual squashing of sets, multisets, orderings, peruvian
>monkey fish, etc., into a single catchall "list" construct.

Because:

>its about allowing the system to be capable of maintaining
>integrity and making formally correct decisions. As far as I can see,
>the domain expert that Marshall specifies above can and *should be* the
>system itself, as defined to it at design time when the domain was
>specified.

Look at it the one way, first. If mushroom, onion needed to be ordered, if they preferred to spread the onion over the mushroom as a preferred practice, if one had to precede the other or else the entity, this event, would simply be wrong, then obviously that order must be accounted. But that's to state the obvious. It's perhaps a contentious point, and this may be which follows. The concern was whether or not this ought to be so constrained, whether or not it was important to record the fact that onion followed mushroom, or if it really didn't matter at all (which fact might also need to be stored, rather than some other or general default). Once you decide, if you have multiple attributes, uniquely named by precedence and role, that's one thing. If you make these dependent in a separate table on some named pizza recipe, then the sort would matter, as well, if you decided that the order could not be ignored. And so on. That would depend on the specific scheme that you use. Received on Mon Feb 27 2006 - 04:47:21 CET