From: ghm@sserve.cc.adfa.oz.au (Geoff Miller)
Subject: Re: DB Comparison - DISAPPOINTING RESULTS
Organization: Australian Defence Force Academy, Canberra, Australia
Date: Mon, 23 Nov 1992 00:37:43 GMT

M22367@mwvm.mitre.org writes:

>Revelation - I worked with Rev/G for about 2 years.  It drove me right up a
>      wall.  I managed to hack it into something reasonable, but I denounce
>      what IMHO is an insurmountable design flaw - every field is variable
>      length.  Rev fans no doubt are about to flame me, but consider: in most
>      database applications, 90% of your data is of known *fixed* length or at
>      least a reasonable maximum can be determined. The 'all variable' paradigm
>      ignores this little fact of life with no profit.  I tried ARev v1 and
>      found it overwhelmingly cumbersome.  Given the wide variety of reasonably
>      good products on the market, I can't see investing the time in Revelation
>      (zip up my Nomex suit for the flames-to-come).

(I was going to e-mail this, but I decided instead that it might be 
worth opening up some discussion.)

The comments about ARev and variable fields apply to Pick variants in
general.  I'm not going to flame, but merely enquire in a non-combustible
manner why you see a particular problem with having fields with no
defined fixed or maximum length?

I agree that many fields in database applications are of a definable
fixed length (at any given time  -  the fields may change in length
due to the introduction of a new coding system, for example), but I
am far less convinced that it is easy to define a reasonable maximum.
What happens when your "reasonable" value becomes "unreasonable"?
How long does it take you to restructure your database?

Every time I have seen this tried I have seen it break.  Take the
following cases  -  what do people consider to be reasonable maxima
for them?

Surname

Address  (and if you break it up into separate fields, how many?)

Postcode  (don't forget to allow for overseas addresses)

Course Name

These are all specific items where I have been very glad that I have
_not_ had to specify a specific maximum length in applications that I
have worked on.  There is also the ability to include a comment field
that can consist of as much text as the user wants to put in, rather 
than having to worry (as I did with one other product) about how
many characters per line and lines per paragraph to allow.

I certainly don't advocate Pick variants as the answer to every
database problem  -  I do find it a very good environment for the
kind of data where you require a very flexible structure.  To give
a specific example  -  we have developed a database for our History
department, covering a lot of data about Australians who served 
overseas in WW1.  We have to some extent had to develop the structure
of this database on the move, as problems have arisen during the
data entry which we had not foreseen (and this was not bad planning  -
you cannot check all the data sources for data on over 300,000 people
to do a comprehensive analysis).  What we did do was ensure that we
were working in an environment which would allow us to adapt the
database easily, and we have (IMHO, and also in the opinion of the
users) succeeded in this.

Geoff Miller (g-miller@adfa.oz.au)
Computer Centre, Australian Defence Force Academy