Re: what are keys and surrogates?

On 18 jan, 00:55, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> Jan Hidders wrote:
> > 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?
>
> Why do you think representations are limited to representing to users?

I don't. I think possreps are. But I could be wrong about their definition. So what is exactly a possrep according to you? Are you saying that the number of possreps of a certain value is by definition the number of ways it can be represented as ... as what?

> How does representing to a user differ from representing to a machine?

You don't get out much, do you? :-)

• Jan Hidders