Re: Database Design Article? -- MIDRANGE-L

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

I once worked at a place that used this technique and as aprogrammer, 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 existingprogram that I need to modify or enhance, and I see that it useslogical file ABCL03, I can not assume that ABCL03 has the fields Ineed that are in physical file ABC. I have to check the file fielddetail of ABCL03 to see what fields are present. Perhaps I need tofind a logical file over ABC with a different sequence. So, inaddition finding an existing logical that has the correctsequence, I also have to look at the detail description of EVERYlogical file I may want to use to find one that has all the fieldsfrom the physical that I need. How much time do you want to spendchecking what fields a logical has versus what fields you want touse? If an existing logical has all the fields I need except one ortwo, do I add them to the logical or create a new logical? When Iwrite a new program using the data in file ABC what logical do Iuse? Once again, in addition to the sequence, I have to look at whatfields 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 fieldsyou need are faster and you can certainly add a new field to thephysical and create a new logical that includes the new field, but Iwould bite the bullet and change the physical, use CHGPF to changethe physical and all the logicals, then recompile the programs thatuse 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.