Re: Principle of Orthogonal Design

On 22 jan, 19:57, mAsterdam <mAster..._at_vrijdag.org> wrote:
> Jan Hidders wrote:
> > mAsterdam wrote:
> >> Jan Hidders wrote:
> >>> JOG wrote:
> >>>>>>> ... I certainly find that appealing to notions
> >>>>>>> of "meaning" within formal design recommendations
> >>>>>>> seems to head towards very slippery ground.
> >>>> ... Years of working with the semantic web,
> >>>> ontologies, expert systems, etc have emphasised to me that
> >>>> "meaning" is only something that can be obtained via situated
> >>>> embodiement within the environment concerned, and that context is
> >>>> far too  complex a beast to be tamed by computerized encoding.
> >>>> As such I'd rather rules appealed to functional dependencies and
> >>>> logical consequents than to appeal to the slippery notion of
> >>>> "meaning".
> >>> Hear hear. But I think the part of POOD that actually does make sense
> >>> and really removes redundancy and update anomalies can be defined that
> >>> way. For example, if there is an inclusion dependency between a
> >>> relation R and S then it makes sense to say that there is overlap in
> >>> meaning.
> >> ?

>

>

>

>

Well, if you have R(a,b) and S(c,d) and a FK R[a,b] to S[c,d], then there is meaning overlap. The inclusion dependencies we are considering have to cover all the attributes of the involved relations.

> >> Slowly, please - where has the 'might' (from the redundancy in
> >> your other post) gone?

>


> > That applied to my improved version of EE's definition of meaning

Ok. For the time being I promise to stick to the following definition:

DEFINITION: Two relations R and S are said to have overlap in meaning if there is an inclusion dependency from all attributes of R to all attributes of S, or vice versa.

Once you are comfortable with this we can move on the the more subtle cases of meaning overlap. To be complete let met also fix the POOD rule for the moment:

DEFINITION: A schema is said to violate POOD if it contains two different relations R and S such that a component of a non-trivial join dependency of R overlaps in meaning with a component of a nontrivial  join dependency of S.

So far so good?

• Jan Hidders