Re: Value

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sat, 23 Feb 2008 22:29:05 +0100
Message-ID: <47c08f6a$0$14354$e4fe514c_at_news.xs4all.nl>


Dmitry A. Kazakov wrote:
> mAsterdam wrote:

>> Dmitry A. Kazakov wrote:
>>> "Value" in this context is a CS term. 
>> I am currently trying to find a helpful piece of text for the cdt 
>> glossary.
>>  From what I read at
>> http://en.wikipedia.org/wiki/Value_%28computer_science%29 ,
>> Value looks like a rather controversial CS term.

>
> I don't see it controversial.

You must have not yet read
http://en.wikipedia.org/wiki/Talk:Value_%28computer_science%29

> I understand why you might dislike it.

The definiens starts with "a sequence of bits". This excludes analog computers. I do think 'value' has meaning, within informatics outside the very limited context the wikipedia page currently adopts to define it.

Is this your understanding? Clever! ;-)

> I support it for the same reason:
> it clearly, though maybe clumsy, states that 1 integer is not 1 float.

That is a (so ISTM) misguided attempt to hide the concept of 'value' behind Type. What is Type IYO?

>> Do you have a better reference?

>
> You mean one, that would support claims of DB-folks? (:-))

I wouldn't have xposted if that would be the case. Disclosure: Though I would be happy to have a description, acceptable to cdt, it is not my motivation for this post (you are aware of that but hey, this is a public forum).

> -------------
> Honestly, I wonder how one could define values otherwise
> while preserving types.

Ah, ok.

> Let me elaborate it a bit informally. The idea of type in
> mathematics was introduced to get rid of antinomies. In CS it is the same
> idea with antinomies extended to the cases of incomputability. We cannot
> judge about equivalences of entities. It could turn undecidable or simply
> too expensive.

So far so good.

> So we just don't.

What 'we' don't do is define value, right? Who is the 'we' here? Type theorists in math and CS? Constructivists? OO folk? co?

> We define entities being values with a
> type assigned to them, merely in order to be able to distinguish them
> *without* computing P(v1=v2). That's the whole idea. Therefore if a v1 is
> of the circle type and v2 is of the ellipse type, that makes them
> automatically distinct. Just *per* construction. This has nothing to do
> with geometry. It is CS.

Hm... opening the circles & ellipses wormcan again. LSP is about behaviour, program correctness, not about values, right? (I did not read the original paper)

How would you go about explaining this to a geometrist? By rejecting the notion of shape (like your rejection of the notion of data)? This creates a whole new perspective on the Disney song: "Īt's a small world after all!".

The loss of rejecting notions, central to other groups is clear. The ability to communicate ideas outside the faculty vanishes. So what is the gain (except idiosyncrasy)?

> Now, when applied to geometry one could reasonably wish v1 and v2
> interchangeable in some contexts. That is called substitutability. Note
> that substitutability assumes that you substitute *one* thing for
> *another*.

So, it is a desirable property in some OO contexts. How is this relevant to wether to define value or not? Where is the dreaded antinomy? Why is it so dreaded?

> So these are *different* things. Substitutability of circle for
> ellipse is a CS model of circles being a subset of ellipses. Note, just a
> model of. No physical subsets involved, though not excluded, when for
> example, circle would inherit the representation of ellipse. Moreover any
> such model is necessary inadequate as a trivial Circle/Ellipse analysis
> shows. So, why all this rant?
>
> Just one final stab. Observe that this framework does not exclude
> "physical" subsets. Neither it specifies the sets where values come from.
> This automatically makes it more general than any other model based on
> subsets of values. Whatever you could do on that basis is already included.

No shapes, no data, no value - three victims already. What's the next concept we'll have to ditch avoiding antinomies? Received on Sat Feb 23 2008 - 22:29:05 CET

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