Re: Normalization was Left AS/400 and Returned

I agree on the multi-format and join logical files.  Or, SQL's views.  And 
highly recommend them for programming, and, most especially, for common 
links the users use in Queries instead of having them join multiple files 
together.

However, he might be right about the performance issue.  For example, 
which would access faster:
1 - A key over customer number and part number in a de-normalized 
order/line file.
2 - A join logical that joins the order/header file with the order/line 
file so that you can see the customer number from the order header file at 
the same time you see the part number of the order line file.  And, keep 
in mind, that a join logical file does not allow keys from more than one 
file, even though I suspect every new release of OS/400 has formed yet 
another DCR requesting this feature.  This might be possible with an index 
on a view in SQL but I don't think that's allowed either.  I know you can 
get the data this way in a normalized database via SQL but it's going to 
do some work under the covers and performance may suffer.

Rob Berendt
-- 
Group Dekko Services, LLC
Dept 01.073
PO Box 2000
Dock 108
6928N 400E
Kendallville, IN 46755
http://www.dekko.com





"Bill Meecham" <bmeecham@xxxxxxxxxxxxxxxxxxxx> 
Sent by: midrange-l-bounces@xxxxxxxxxxxx
05/03/2005 01:33 PM
Please respond to
Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>


To
"Midrange Systems Technical Discussion" <midrange-l@xxxxxxxxxxxx>
cc

Subject
Re: Left AS/400 and Returned






That's not necessarily true since multi-format and join logical files can 
be created and created much easier when the database is normalized.  The 
reason shops don't normalize is more likely because it's difficult to 
master and there is little perceived benefit.  Borrowing from another 
thread, that's a large part of what case tools help with....normalization 
and 'virtualization' of fields. 
  ----- Original Message ----- 
  From: michael@xxxxxxxxxxxxxxxxxx 
  To: Midrange Systems Technical Discussion 
  Sent: Tuesday, May 03, 2005 2:25 PM
  Subject: RE: Left AS/400 and Returned


  The reason that most vendors and shops don't have normalized databases
  is because most vendors and shops don't use the data store on the
  iSeries as a database - it's used as a system of indexed files.
  Normalization in that scenario can hurt performance, because the
  program would need to chain to several files to gather the information
  needed to present to the user. There's no doubt that normalization is a
  good thing for a database (at least 3NF), but normalization for indexed
  files isn't as important or desired.

-- 
This is the Midrange Systems Technical Discussion (MIDRANGE-L) mailing 
list
To post a message email: MIDRANGE-L@xxxxxxxxxxxx
To subscribe, unsubscribe, or change list options,
visit: http://lists.midrange.com/mailman/listinfo/midrange-l
or email: MIDRANGE-L-request@xxxxxxxxxxxx
Before posting, please take a moment to review the archives
at http://archive.midrange.com/midrange-l.