Re: Database Design Article?

[Dave Murvin <davem@xxxxxxxx>]

I don't recall the article, but from a programmer point of view, I 
would think twice about only having selected physical file field 
names in each logical file.

I once worked at a place that used this technique and as a 
programmer, I found it very aggravating and a huge time waster.  For example:

Suppose ABC is the physical file and ABCL01, ABCL02, ABCL03 etc. 
represent the logical files over ABC.  When I work on an existing 
program that I need to modify or enhance, and I see that it uses 
logical file ABCL03, I can not assume that ABCL03 has the fields I 
need that are in physical file ABC.  I have to check the file field 
detail of ABCL03 to see what fields are present.  Perhaps I need to 
find a logical file over ABC with a different sequence.  So, in 
addition finding an existing logical that has the correct 
sequence,  I also have to look at the detail description of EVERY 
logical file I may want to use to find one that has all the fields 
from the physical that I need.  How much time do you want to spend 
checking what fields a logical has versus what fields you want to 
use?   If an existing logical has all the fields I need except one or 
two, do I add them to the logical or create a new logical?  When I 
write a new program using the data in file ABC what logical do I 
use?  Once again, in addition to the sequence, I have to look at what 
fields are included in each potential logical versus what fields I need to use.

I think I have seen comments that logical files with only the fields 
you need are faster and you can certainly add a new field to the 
physical and create a new logical that includes the new field, but I 
would bite the bullet and change the physical, use CHGPF to change 
the physical and all the logicals, then recompile the programs that 
use them.  I think it will be much easier in the long run.

At 03:21 PM 1/24/2007, you wrote:
> A few weeks ago I came across an article about changing how you use
> physical and logical files.  I thought it was very interesting, but got
> busy and never finished the article.  Not I cannot seem to find it
> anywhere.
>
> Essentially, the author was advocating using logical files with only the
> fields the application is using.  This would enable you to add additional
> fields to the physical file without the need to recompile every logical
> and associated programs.
>
> Did anyone else see (or write) this article?

Dave Murvin
DRM Enterprises, Inc.