Re: boolean datatype ... wtf?

On 1 okt, 14:41, Tony Andrews <tony.andrew..._at_gmail.com> wrote:
> On Sep 30, 1:04 pm, Erwin <e.sm..._at_myonline.be> wrote:
>
> > On 30 sep, 12:32, Tony Andrews <tony.andrew..._at_gmail.com> wrote:
> > > Or we could create a plethora of tables like:
> > >  create table applications_with_garages (application_id references
> > > applications primary key);
> > >  create table applications_with_immobolisers (application_id
> > > references applications primary key);
> > > ... etc.
>
> > > That may be the right approach in a theoretical true RDBMS, but I'm
> > > pretty sure it would get me sacked as a lunatic in any SQL-based DBMS
> > > team!
>
> > If your SQL-based DBMS had proper physical data independence, then I
> > am quite convinced your claim would be false.
>
> But would this unary table approach to avoid a Boolean attribute
> really be considered good practice in a true RDBMS?  If I want to know
> "does the applicant's car have an immboliser", is the absence of a row
> in applications_with_immobilisers sufficient to answer it?  I thought
> that was a proposed solution to missing information ("it is unknown
> whether the applicant's car has an immobiliser"), now it seems to be
> acting as available information - i.e. the predicate "applicant 123's
> car does not have an immboliser".  Seems dubious to "record" a known
> fact by, er, not recording it.

Does this make a meaningful difference ?

I mean, you came up with the example of checkboxes on paper. The checkbox on paper can be "marked" if the corresponding label/property is "true". If the checkbox on paper is not marked, you interpret that as "false", no ? You wouldn't consider/interpret this as "unanswered", or "unknown", or whatever, no ?

If the answer is two-way, then those two ways are isomorphic to "tuple present"/"tuple absent", no ? And "unknown"/"unanswered" simply doesn't enter the picture, no ?

If you want to _explicitly_ take the option of "unknown"/"unanswered" into account, then on the paper version, you would be _forced_ to provide an _additional_ checkbox saying "I know the answer to the next question", or "You can consider the next checkbox as having been answered", no ? Received on Fri Oct 01 2010 - 15:54:26 CEST