Re: Canonical DB

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sat, 24 Jun 2006 14:18:26 +0200
Message-ID: <449d2d28$0$31644$e4fe514c@news.xs4all.nl>

Dmitry A. Kazakov wrote:
> mAsterdam wrote:

>> ...A correct model would have the constraints
>> in place to preserve the invariant of the
>> structure while allowing all valid modifications.

>
> Yes. But the problem is (apart from expressing the constraints, which
> itself might be far from trivial: like an acyclic graph constraint etc),
> that you might lose the structure.

Is your 'lose the structure' just another way of stating 'the invariant is not preserved', or is there more to it?

> To me this all is the infamous LSP problem.

LSP? Label-switch path as in
http://www.ietf.org/rfc/rfc3209.txt ?

> You have some set of things (whatever they be, relations or
> ellipses) with some structure (algebra), you put a constraint on the set
> (so you get graphs or circles), and see that some statements about the set
> become wrong.

Yep, same thing happens if you fail to put on a constraint which should be there.

> My favorite examples always integers, sorry. (:-)), Put n>0 on integers and
> you will lose negative inverse.
>
> The point is that it is really, really fundamental. Circles aren't ellipses
> though any circle is an ellipse. The structure is different. Same with
> trees vs. tables.
>
>

>>I tried modeling the C3 MRO relationally
>>but haven't found a solution (or the conviction
>>that it can't be done) yet.
>>
>>http://www.python.org/2.3/mro.html
>>
>>and (background)
>>
>>http://www.webcom.com/haahr/dylan/linearization-oopsla96.html#C3-line
>>
>>It is a nice (and IMHO very useful) challenge.
>>Any takers?

>
>
> Ah, multiple dispatch, it is a hard problem. I'm unsatisfied with presently
> existing solutions.
>
> BTW, it might be interesting to consider relational structures of types.

Yes, please. Could you provide some background (and maybe some references to/elaboration on to presently existing solutions)?

-- 
"The person who says it cannot be done
should not interrupt the person doing it."
Chinese Proverb.

Received on Sat Jun 24 2006 - 07:18:26 CDT