RE: DBA Question

>> Did you know that a logical can select only certain fields from a
>> physical file?  And that you can update the database using such a
>> logical, thereby gaining what you term database independence?  You can
>> even have JOIN logicals on an iSeries, albeit with limitations that SQL
>> JOINs aren't subject to (mostly because SQL JOINs have the option of
>> building intermediate tables when necessary).

Joe, you might want to read what I wrote again. You will note that I was 
referring to exactly the scenario you are describing. Using a logical file as 
logical view, not just as just as a file system file. Field select, joins, etc. 
 

>> We've done this sort of thing for many years, but we are careful about
>> it, because updating only a partial record is VERY dangerous.  On
>> writes, you can at least see NULL values, but a partially updated record
>> can be a very bad thing.

Ok, huh. What do you mean by a partial record? Are you talking about an update 
of single field? Why would that be dangerous? A write using partial fields can 
be dangerous, although if the database is setup correctly, it shouldn't be.  

>> In any case, the idea of changing the underlying tables of a database
>> without having to change any programs is simply silly.  Some programs
>> will have to change or else the changes are meaningless.  In the DB2/400
>> world, we simply recompile the ones that don't use the new fields and
>> we're done; a simple added step that really doesn't bother anyone but
>> the SQL folks.

Ok, you have lost my again. I am not saying that every program does not have to 
change. Maybe only one program would need to change. 

Not sure what you mean by "We simply recompile the one's that don't use the new 
field". Do you mean, going through and recompiling every program in the system 
that uses the table? I won't call that simple. They changed one table at my 
company recently and had to recompile 700 programs. Had one analyst working on 
it for 5 weeks and that was with Turnover doing the work. 

In most companies, they don't even try. They just create an extension table and 
then when they have too many programs using the extension, they create another 
extension and so on. In some packages, I see this getting real interesting. 

> In a file system, logical and physical views of the data are the same,
> that is you bring the whole file into every program. As far as the
program
> knows, theirs is the physical view of the data.

>> This is NOT a logical file on the iSeries... thus I question the rest of
>> the discussion.

My point is that on the AS/400 we use the database as a file system. How many 
times have you seen a logical file used as something except to build an index 
with the entire record brought in?

What does this statement have to do with logical files? I am talking about a 
file system and the concept of a file system on, for example, a S/36.