Re: On the usefulness of tables definitions in RM...

On 20/08/2010 9:16 AM, Roy Hann wrote:
> Cimode wrote:
>
>> I lately came to the conclusion that teaching relation structures and
>> manipulations by using tables inherently induces a bias to think of
>> relations as relation values as opposed to relation variables.
>> However, I believe that tables are elements of the presentation layer
>> since they are only *one* possible representation in time of a
>> specific relation.
>>
>> I am curious on whether this confuses more than it helps as far as
>> operation definitions are concerned. What representations are to be
>> preferred to avoid confusions ? In what context ?
>>
>>
>> Opinions welcome.
>
> When I am teaching I start by writing out a few propositions in full,
> but mixing up the order, and I draw attention to the fact that I am
> doing it.
>
> I then invite the class to tell me if I have repeated myself anywhere
> (which I usually haven't).
>
> I then tell them that to simplify my presentation and to make it easier
> to answer questions like that "at a glance" *BUT FOR NO OTHER REASON*, I
> will discipline myself to always write the propositions in a single
> consistent form.
>
> I then point out that a single predicate can be written which is of a
> form that all the propositions fit, so I can leave out all the
> extraneous verbiage and just *list* the values to plug into the
> predicate.
>
> I then re-write all my propositions just as lists of values, neatly
> lined up, so that it appears tabular.
>
> I then remind the class that the tabular appearance is merely a happy
> accident.
>

Regarding repetition, I don't think there's anything incorrect about it in principle, although I imagine it might cause confusion when the average dbms operates. I'd go so far as to say that even logical redundancy wouldn't matter with a better dbms that normalized, although I can understand why people find that doing the normalizing manually helps expose errors in data design and possibly there are some cases where it is impossible or close to impossible to normalize in a reasonable amount of machine time.

People like repetition, is it just machines that make it awkward? Received on Fri Aug 20 2010 - 21:22:37 CEST