Re: what are keys and surrogates?

On Jan 19, 8:35 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> Jan Hidders wrote:
> > On 18 jan, 18:33, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
> >>Jan Hidders wrote:
>
> >>>On 18 jan, 16:55, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
> >>>>Jan Hidders wrote:
>
> >>>>>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?

Badour seems hung up on this, but it seems reasonable to assume the logical-physical distinction has very much to do with distinction between representations that are visible or not visible to users, with an appropriate definition of "user". Otherwise what is the logicalphysical  distinction about?

> >>>>>I don't. I think possreps are. But I could be wrong about their
> >>>>>definition.
>
> >>>>I strongly suspect you are.
>
> >>>>>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?
>
> >>>>I don't understand the part starting with "as". I would punctuate the
> >>>>sentence there instead.
>
> >>>I think you want to be more specific on what a representation exactly
> >>>is. That it should be something that can be presented by a computer to
> >>>a user on screen or a paper, for example.
>
> >>A poor example.
>
> > *shrug* Unless you are going to substantiate that, that is not really
> > a very interesting response.
>
> I don't see any need to respond to straw men beyond observing that they
> are straw men. So, you want to assume that "possible representations"
> relates exclusively to human users to what end? To prove your axiom?
> Your axiom is false in the first place.
>
> Assuming it to prove it is mental masturbation. If you want to engage in
> such activities, please do so in private.

Jan simply asked Badour to clarify what is meant by a representation and Badour responds with the straw man defence.

> >>A string, would be my first
>
> >>>guess. Other representations like smoke signs, chalk marks, a series
> >>>of coughs, etc. are clearly not very relevant for the question in how
> >>>many ways you can map it to the physical layer.
>
> >>I disagree.
>
> > No kidding. :-)
>
> >>>>>>How does representing to a user differ from representing to a machine?
>
> >>>>>You don't get out much, do you? :-)
>
> >>>>That kind of man-machine interface never even occured to me. One wonders
> >>>>what causes your mind to wander in that direction.
>
> >>>I was only half kidding. A possrep is a notion at the logical level,
> >>>and therefore a matter of agreement between people. It is how a
> >>>certain set of persons agree to communicate a certain concept. For a
> >>>mapping to a physical level there is no such agreement necessary.
>
> >>Indeed. However, every mapping to the physical level starts with a
> >>possible representation. Double or triple the number of possible
> >>representations, and one doubles or triples the number of possible
> >>physical representations.

Note this well!

> > No, it doesn't. Increasing or decreasing the number of possible
> > representations does not influence the number of ways you can store
> > it.
>
> You are talking nonsense. One cannot increase or decrease the possible
> representations for a data type. What's possible is always possible and
> what's not is not.

On its face that contradicts Badour's earlier statement where he talks about doubling or tripling the number of possible representations.

Perhaps he would say his previous statement concerned comparisons of *different* data types; however it seems remarkable to claim that unrelated data types would always exhibit such a similar ratio of number of logical to physical representations.

For a given data type the possible logical representations are *user defined*, and therefore one can make sense of Jan's remark of increasing or decreasing the possible
representations. There is no mathematically defined concept of an absolute set of all possible logical representations. Evidently such a set would be infinite. It comes down to human judgement as to which ones are deemed useful. For example, representing the dimensions of a rectangle using the quarter-width and the fifth root of the radius of the circle of equal area is technically a possible logical representation, but hardly practical.

> It might give you new ideas, but does note create options that you
>
> > did not have already before. There simply is no direct relationship.

Exactly.

> I have no idea where you get the idea that a data type with exactly two
> possible representations has exactly equal flexibility at the physical
> level as a data type with ten possible representations. The idea is
> absurd on its face.
>
> I have no choice but to cite Date's _Principle of Incoherence_.

"exactly equal flexibility" are strong words...

I don't believe Jan stated nor implied that different data types have the same number of physical representations.

> >>>makes these notions fundamentally different. More to the point, you
> >>>could have six ways to represent the number 5, but let the DBMS store
> >>>it always in the same way.
>
> >>But one would have to choose a possible representation. Choosing a
> >>representation that does not possibly represent the value seems pointless.
>
> > It would do so by definition.
>
> And the more possible representations, the more options one has at the
> physical level. I don't know why you have such difficulty with such a
> simple concept.

Shouldn't Badour merely say there will be some positive statistical correlation?

>
> >> Or you could have only way to represent it,
>
> >>>but have six ways of storing it.
>
> >>If one has six ways of storing it, presumably one has six ways of
> >>storing each of the possible representations. Thus, the number of
> >>physical representations grows linearly with the possible representations.

Am I reading this right? Badour seems to assume that a given physical representation coincides with (only) one of the logical representations. Does he think there will actually be 36 distinct physical representations?

[snipped insults initiated by Badour] Received on Sat Jan 19 2008 - 02:48:37 CET