Re: Why all the max length constraints?

From: David Cressey <dcressey_at_verizon.net>
Date: Tue, 30 May 2006 21:33:51 GMT
Message-ID: <3T2fg.12$DO5.5_at_trndny06>


"dawn" <dawnwolthuis_at_gmail.com> wrote in message news:1148773922.267863.170930_at_j55g2000cwa.googlegroups.com...
> [OK, here is my next "stupid question" as I cut a path in my study of
> the RM. Those teachers who just want to tell this student how ignorant
> she is are welcome to sit this out as I really am hoping to
> understand.]
>
> In SQL-DBMS's, like VSAM (and other indexed sequential files before
> them) a lot of attributes are specified with max length constraints.
> While there are some attributes where this constraint is related to a
> conceptual constraint (from the analysis phase), these lengths are
> often introduced for the logical model or implemenation in the DBMS.
>
> In other words, when mapping from the conceptual (analysis) to the
> logical (design) data models (pick the terms you like best for these),
> these constraints are designed for many attributes that have no such
> conceptual/business limits (if implemented with a paper system, there
> would be no such limit, for example).
>
> Is there something about the RM that would prompt all (or most?)
> existing implementations (however flawed) to drive developers to add in
> these constraints for performance, space saving, or other reasons? I
> realize there can be variable length attributes, but specifying a max
> field length still seems to be the norm (is that still the case?)

This newsgroup has answered this question. The answer is no.

The DBMS engineers (which is what I guess you mean by "developers") may have had reasons for imposing these limitations, but they were not driven by the RM.

If you want to talk about what *other* objectives might have led them to impose such limitations, we can talk about that. But you need to rephrase the question. Received on Tue May 30 2006 - 23:33:51 CEST

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