Hierarchical vs. Parallel linkage
Matt Ohmes
mohmes at us.ibm.com
Fri Mar 6 08:52:06 CST 2015
Hey Richard!
You are probably one of the last people who remember my old MattO (Oh, not
zero) tag. :-)
I don't know if there are still PH conventions, but I doubt it. Oddly
enough I gave a more complete version of this many, many years ago at a
Cognos convention and it was my biggest ego boost moment. The room not
only filled completely, but there were people sitting on the floor at my
feet so they could see it!
I wish I still had that original paper, as it seems to be a pretty
confusing topic still. (Anyone have one in their archives?)
Also, If you have a QTP with all those files, you might also be interested
in another paper I wrote (years ago) called the "Care and Feeding of QTP".
I have a PDF of it still I can send you if you'd like (I can't post it to
the list, if I recall). However, that has more to do with output timing
than hierarchical vs. parallel linkage.
My main advice for debugging Access statements has always been, take the
Access and put it in Quiz and write a VERY basic Report statement that
dumps something from every files. Then go look at the files individually
and make sure they match what you see. If that works, they your problem
is elsewhere. And honestly, with QTP, it is usually the "elsewhere" that
is the problem. :-)
This has been fun!
Cheers,
Matt
From: "Richard Witkopp" <RWitkopp at phxa.com>
To: "PowerHouse listserver" <powerh-l at lists.sowder.com>
Date: 03/05/2015 06:29 PM
Subject: RE: Hierarchical vs. Parallel linkage
Sent by: powerh-l-bounces+mohmes=us.ibm.com at lists.sowder.com
Nice, not-a-zero!
Are there still Powerhoose conventions? This would make a good
presentation.
I need to re-read this thing about 4 times. I’ve got a qtp with about 5
parallel legs and 3 hierarchical files down each leg and it doesn’t do
what it looks like it should do.
From: powerh-l-bounces+rwitkopp=phxa.com at lists.sowder.com [
mailto:powerh-l-bounces+rwitkopp=phxa.com at lists.sowder.com] On Behalf Of
Matt Ohmes
Sent: Thursday, March 05, 2015 3:57 PM
To: PowerHouse listserver
Subject: Hierarchical vs. Parallel linkage
Hi all,
I promised I would write up something on the differences between
Hierarchical and Parallel linkage in Quiz (and QTP), so here we go. (And
for those of you who know all this already, please forgive my trip down
memory lane.)
Oh, and I'm assuming no bugs in the product regarding syntax. :-)
Differences between Hierarchical and Parallel linkage in Quiz (and QTP)
In all examples below, we will use 3 files. Assume all are indexed files,
keyed on Emp_No
File Employees: 5 records;
Emp_No Emp_Name
1 Bob
2 Mary
3 Pat
4 Kim
5 Sean
File Paychecks: 5 records
Emp_No Pay_Date Amt
1 2015-01-01 100 (Bob)
1 2015-01-15 200 (Bob)
2 2015-01-01 300 (Mary)
2 2015-01-15 400 (Mary)
3 2015-01-15 600 (Pat)
Note: 4 Kim and 5 Sean just started and have not been paid yet)
File Dependents: 4 records;
Emp_No Dep_Name
1 Bob Jr (Bob's 1st dependent)
1 Bobbie (Bob's 2nd dependent)
2 Marie (Mary's dependent)
5 Shawn (Sean's dependent)
Note: 3 Pat and 4 Kim do not have any dependents
This will be my Report statement for ALL examples:
Report &
Emp_No of Employees &
Emp_Name of Employees &
Pay_Date of Paychecks &
Amt of Paychecks &
Dep_Name of Dependents
First Hierarchical linkage:
Access Employees &
Link Emp_No of Employees to Emp_No of Paychecks &
Link Emp_No of Employees to Emp_No of Dependents
Emp_No Emp_Name Pay_Date Amt Dep_Name
1 Bob 2015-01-01 100 Bob Jr
1 Bob 2015-01-01 100 Bobbie
1 Bob 2015-01-15 200 Bob Jr
1 Bob 2015-01-15 200 Bobbie
2 Mary 2015-01-01 300 Marie
2 Mary 2015-01-15 400 Marie
Obvious problems. Pat, Kim, and Sean are not showing up at all because no
files are optional. I'm assuming the use of Optional in hierarchical
linkage is well understood so I won't go into that discussion here. This
post is about parallel linkage. :-)
A bigger problem with the report is that paycheck and dependent records
are being duplicated. Hierarchical linkage is simply wrong for this data;
the results make no sense.
Using hierarchical linkage for this data is essentially saying, for each
paycheck an employee has received, read down the list of all their
dependents. That makes no sense. Just as it would make no sense to say,
for each dependent an employee has, show me every time they have been
paid. The number of paychecks I receive is based on how long I have
worked for my employeer, not how many dependents I have. Similarly, the
number of dependents I have is not based on how long I have worked for my
employer.
Paychecks and Dependents are both, obviously related to Employees, but
they are NOT RELATED TO ONE ANOTHER.
Instead of one of these files "driving" the other, they should be read in
parallel; i.e. at the same time. THIS is why we have parallel linkage.
Parallel linkage is saying, for each employee, show me each of their
paychecks AND each of their dependents.
Let's try parallel linkage in the Access statement and what that does to
our report results.
Access Employees &
Link Emp_No of Employees to Emp_No of Paychecks &
AND Emp_No of Employees to Emp_No of Dependents
Emp_No Emp_Name Pay_Date Amt Dep_Name
1 Bob 2015-01-01 100 Bob Jr
1 Bob 2015-01-15 200 Bobbie
2 Mary 2015-01-01 300 Marie
2 Mary 2015-01-15 400
3 Pat 2015-01-15 600
5 Sean Shawn
This makes more sense for this data. Each paycheck is reported once and
each dependent is reported once.
Notice, as long as there is at least one record FROM ANY of the parallel
files you get a record complex returned. Parallel files are, more or less,
"semi-optional".
However, also notice employee 4 Kim was not reported. This was because
Kim did not have any paychecks (yet) or dependents. If you want to see Kim
on the report as well, make ANY of the parallel files optional; it doesn't
make any difference which one because of the "semi-optional" nature of
parallel files.
Access Employees &
Link Emp_No of Employees to Emp_No of Paychecks &
AND Emp_No of Employees to Emp_No of Dependents Optional
Emp_No Emp_Name Pay_Date Amt Dep_Name
1 Bob 2015-01-01 100 Bob Jr
1 Bob 2015-01-15 200 Bobbie
2 Mary 2015-01-01 300 Marie
2 Mary 2015-01-15 400
3 Pat 2015-01-15 600
4 Kim
5 Sean Shawn
To be honest, parallel linkage is not that common. It is fair to ask, "If
two files aren't related to one another, why are you writing a report with
both of them on it?" But it does have its uses from time to time.
I hope that explanation helps. (It was fun writing about good old Quiz
again after all these years.)
Cheers,
Matt
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