 
Senior Member
Cominatorial Design/Ortogonal Array HELP!! I have just finished reading the article in STQE Orthogonally Speaking by Elfriede. I have read a few things here and there on the subject but this article has really got me interested in the topic.
My problem is that what I am finding on it is soooooo over my head that I can't get anything out of it. Or it does not relate closely enough to testing.
Please help me in finding resources on this.

ER,
Sr. QA Lead 
Senior Member
Re: Cominatorial Design/Ortogonal Array HELP!! You might find this site interesting: http://aetgweb.argreenhouse.com/
They have a 2 week online demo for which you can register. There are also some white papers there on the subject.
PS: After reading Elfriede's article today, I started spending my lunch hour trying to figure out how to write a program to take a set of 3 items, each with 3 possible values, and find the minimum set of test cases that exercised each pairwise combination. I've not come up with a solution yet.

Charles Reace
charles{DOT}reace{AT}verizon{DOT}net
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Super Member
Re: Cominatorial Design/Ortogonal Array HELP!! <BLOCKQUOTE><font size="1" face="Verdana, Arial, Helvetica">quote:</font><HR>Originally posted by Charles Reace: You might find this site interesting: http://aetgweb.argreenhouse.com/
They have a 2 week online demo for which you can register. There are also some white papers there on the subject.
PS: After reading Elfriede's article today, I started spending my lunch hour trying to figure out how to write a program to take a set of 3 items, each with 3 possible values, and find the minimum set of test cases that exercised each pairwise combination. I've not come up with a solution yet. <HR></BLOCKQUOTE>
Hi Charles,
Since you have read my article “Orthogonally Speaking” in the current edition of STQE Magazine (www.stqemagazine.com), go to page 48 of the article, and take a look at Table 1 “Sample Array.”
Use this sample array to find the pairwise combinations for 3 parameters (A,B,C) that each have 3 possible values (1,2,3).
Here is a simplified exercise (given Table 1 of the Sample Array 3 parameters/3 values):
Replace column A with the parameter “Credit Card,” replace Column B with the parameter “Credit Card Number“, replace column C with the parameter “Expiration Date”.
Credit Card (column A) can have the following values (in this simplified example):
Amex, Discover, Visa (items to replace the row values in column A)
1 = Amex (the 1’a in the A column get replaced with Amex)
2 = Discover (the 2’s in the A column get replaced with Discover)
3 = Visa (the 3’s in the A column get replaced with Visa)
Credit Card Number (column B) can have the following values (in this simplified example):
Valid, Incorrect length, Invalid digits
1 = Valid (the 1’s in the B column get replaced with Valid data)
2 = Incorrect length (the 2’s in the B column get replaced with Incorrect length data)
3 = Invalid digits (the 3’s in the B column get replaced with Invalid digit data)
Expiration Date (column C) can have the following values (in this simplified example):
Valid, Incorrect length, Invalid digits
1 = Valid (the 1’s in the C column get replaced with Valid data)
2 = Incorrect length (the 2’s in the C column get replaced with Incorrect length data)
3 = Invalid digits (the 3’s in that C column get replaced with Invalid digit data)
Try this exercise.
Using this orthogonal array narrows down the exhaustive number of 27 test cases, to 9 test cases. The test case savings get bigger as the parameters and values become larger.
This is a simplified example. Most of us have to test with many more parameters and values, i.e. on my current project, we ended up using an Orthogonal Array that generated 17,000+ test cases  in an automated fashion. Without the use of Orthogonal Arrays, the number of combinations and variations of required test cases would have been in the hundredofthousands.
I’d suggest, that you don’t apply Orthogonal arrays manually (see page 51 of this article). As the arrays get bigger, manual implementation becomes tedious, errorprone and most of all timeconsuming and a maintenance nightmare.
Download the freeware from Prof. Art Owen Art Owen, orthogonal arrays for computer experiments, StatLab, Dept of Statistics at Carnegie Mellon University, lib.stat.cmu.edu/designs to generate the size of arrays needed for your project.
Then write a VB script (or use any other type of language) to replace your test parameters and values with the values in the array.
There are also Orthogonal Array tools on the market. For more info on those go to www.stqemagazine.com, then click on StickyNotes (scroll to my article “Orthogonally Speaking” for related info).
HTH,
Elfriede

Elfriede Dustin
Author (with Rashka, Paul)of book "Automated Software Testing", July ‘99
Author (with Rashka, McDiarmid) of book "Quality Web Systems: Performance, Security & Usability", August ‘01 www.autotestco.com www.qualitywebsys.com
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