Re: Why all the max length constraints?

dawn wrote:
> Keith H Duggar wrote:
>

>>dawn wrote:
>>
>>>...  Why give a max length to
>>>an attribute that doesn't conceptually require such?  Why
>>>can't the DBMS handle that for you (efficiently, of
>>>course)?
>>
>>Who says they cannot? Do you realize that even if no DBMS
>>implementation has yet done so, this is not evidence of
>>impossibility.

> That would be the reason for my question. I am asking what is the
> reason that all of the implementations of the RM work with a max length
> constraint on attributes. So I should have written "why couldn't the
> DBMS...", perhaps, but most would understand the rhetorical technique,
> I would think.

Even better:
"Why don't the DB designers let the DBMS handle it." (Summary of my answer your OP: Because they trust specifying it from earlier solutions.)

As soon as you say "can't" in relation to a pet tool or model you are waving a red cloth in front of a bull.

Not unlike Neo's unfounded "prolog can't do this" or "RM can't do that" statements repeated ad nauseam.

This gives room to responses like:

>>This is a classic example of argument from
>>ignorance or the burden of proof logical fallacy.

You shouldn't have waved the red towel :-)

>>And yet
>>you imply this fallacious claim from the start of the
>>thread. Do you understand this is a logical fallacy?

> I have no answer I'm driving at, but am trying to understand. I have
> worked from the user to the app-implementation of many varied "data
> processing" systems, but have never written a DBMS tool. I do not have
> enough understanding of what is under the covers of any dbms to know
> what the reason would be for the max length constraints on attributes.

Here you are suggesting again they aren't part of the database design but part of the dbms. They are not - another red towel. You could easily make your statement in a way which shows you understand that difference.

[snip]

> I could read numerous papers and learn enough so that I could produce
> an implementation of the RM myself, at which point I would know why I
> wanted those attribute length constraints.

The db designer determines attribute length constraints, not the dbms. Why do you ignore this difference?

[snip] Received on Sun May 28 2006 - 16:13:12 CEST