Re: Why all the max length constraints?

"dawn" <dawnwolthuis_at_gmail.com> wrote in message news:1148926992.308719.48250_at_g10g2000cwb.googlegroups.com...
>
> David Cressey wrote:
> > "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.
> >
> > Is VSAM really a DBMS? I looked up VSAM in wikipedia, and the
definition I
> > found suggests that VSAM is NOT a DBMS, although both IMS and DB2 are
> > layered upon it.
>
> I agree that VSAM is not a DBMS. I did not intend to imply they would
> be categorized as one.

OK. I didn't pick up on the comma before the word "like" in your original post. I thought you were giving VSAM as an example.

Now that we've got that nailed down, on to the next issue: The consensus of the responders (including me) is that there is nothing inherent in the RM that would force declaration of a max length for character strings. There's nothing inherent in SQL either, afaik. There are plenty of systems that have nothing to do with RM or SQL that impose character limits on strings.

COBOL is one you should be familiar with.

There are plenty of systems that have nothing to do with MV that permit manipulation of variable length strings, without an explicint max declared. BASIC is one you should be familiar with.

With regard to implementation internals, how deep do you want to go?

With regard to increased marketability of products that work with fixed length strings, that's a whole different matter. And it's where RM theory, and the design choices made by DBMS egineers start to diverge. We could have a separate discussion about that. Received on Mon May 29 2006 - 21:25:09 CEST