Re: Type-free Circles and Ellipses [T]

> On Thu, 30 Aug 2001 10:05:31 GMT, dmitry_at_elros.cbb-automation.de
> (Dmitry A. Kazakov) wrote:
>
> >If you are arguing against the limitations of the subtype relations
> >usual to the modern OO languages, I am with you. There is nothing
> >fundamental that requires the subtype relation be a tree.
>
> In most of the useful theory that I have seen, the subtype relation is
> described as forming a lattice. Of course, for that to work, you have
> to be able to think about types that have never been written down, but
> which are derived as meets or joins of other types. Of the types you
> start with, some are written down explicitly, and others are inferred
> from various language constructs, and the types used in them.
>
> In the language we invented when I was working on the ANSA
> computational model, expressions and variables had different kinds of
> types. The two kinds of types had conformance relations which each
> formed semi-lattices, but opposite ways up. The other thing we did was
> to ban the use of the word 'subtype' in our reports and discussions;
> we did that because the emotive connotations, the confusion with
> inheritance and the potential to be confused about which way was 'up'
> made it a liability.
>
> Ever since then I have found the type systems in languages that
> purport to be OO deeply unsatisfying.

Is that language documented on-line anywhere by chance?

I see no distinct boundary between "sub-types" and "attributes". One can be exchanged for the other. Thus, the choices seem to be:

1. use only subtypes to represent variation
2. use only attributes to represent variation
3. mixed

I don't think anybody supports #1, so I will ignore it.

Now, if we mix them (#3), there should be some criteria for when to use one or the other for each feature.

All arguments for *some* features being "important enough to be promoted to a subclass" have so far been suspect. Importance changes and is
relative to a user's or application section's need.

When you walk into an office, the drinking fountian is of minor importance to most people. It may be the last thing your eye notices. However, if you are very thirsty, it is the *first* thing you notice. Thus, in your mind you, for the moment, offices are divided into

OfficesWithDrinkingFountains
and
OfficesWithOutDrinkingFountains.

Thus, I lean toward #2 until better justification and criteria and stability for importance ranking comes along.

>
> --
> Owen Rees - opinions expressed here are mine; for the full disclaimer
> visit <http://www.users.waitrose.com/~owenrees/index.html#disclaimer>
>

-T- Received on Fri Aug 31 2001 - 02:41:07 CEST