Re: what are keys and surrogates?

On Jan 17, 10:29 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> Jan Hidders wrote:
> > On 17 jan, 14:40, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
> >>Marshall wrote:
>
> >>>On Jan 10, 7:07 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
> >>>>Marshall wrote:
>
> >>>>>>Is "constructor" the same as what C. Date calls a "selector"?
>
> >>>>>Yes. Date calls it a selector, and the entire rest of the world
> >>>>>calls it a constructor. :-)
>
> >>>>Except "selector" has no concept of physically building anything in storage.
>
> >>>Okay. Just specifying a value, or a kind of value, yes?
> >>>That's more or less what I understand the most general
> >>>definition of the word "constructor" to mean. The OOP
> >>>world uses it a bit more specifically.
>
> >>I suspect the word originates in the OOP world, and it strongly suggests
> >>building something physical.
>
> >>>>>I have no strong feelings about encapsulated ADTs; what
> >>>>>Date calls ... uh. Shit. I can't remember what he calls them.
> >>>>>I don't entirely see the reason for them. Performance I guess?
>
> >>>>Types? Possible representations? Type generators? Only the first is an
> >>>>ADT, but I am curious whether you meant one of the others.
>
> >>>Possreps! That's the one!
>
> >>Having multiple possible representations for the same type allows data
> >>independence--especially physical independence.
>
> > You think the number of possible representations and the number of
> > possible ways to store something in memory or on disk are related?
> > Why?
>
> The latter grows linearly with the former.

Why? Seriously. Why do you think there is a relationship at all? Why would the number of ways a value can be represented to the user (something which a matter of definition and/or convention) have any bearing on how many ways there are to map it to 1's and 0's?

• Jan Hidders