Observable States May be Necessary
When Using COTS Products
Rick Botta1, Zach Bahill3 and Terry Bahill1,2,*
1BAE SYSTEMS, 10920 Technology Place, San Diego, CA 92127
2Systems and Industrial Engineering, University of Arizona, Tucson, AZ 85721-0020
3Boeing Integrated Defense Systems, Kent, WA
*Author to whom correspondence should be addressed (e-mail terry@sie.arizona.edu).
Copyright © 2005 by BAE Systems. Published and used by INCOSE with permission.
Abstract. In order to use commercial off the shelf (COTS) products, the engineer must be able to prove that the COTS product is equivalent to the specified design. In most cases, this requires observable states, which are usually not available. Other techniques that have been used in lieu of proving system equivalence include creating multiple reset (or test) states and proving input/output equivalence with respect to these initial state pairs, designing built-in self-tests, building observers to estimate the system states and adding extra outputs that imply the states. This paper also gives examples where states are necessary and unnecessary in modeling systems.
THE DECISION OF MAKE VERSUS REUSE VERSUS BUY
Are you going to make, reuse or buy lunch today? You could go to a restaurant and buy a hamburger. Or you could reuse your leftover pizza (if it’s not moldy). Or you could decide to make lunch. In which case, you could go to the grocery store and buy hamburger, lettuce, tomatoes, cheese, buns and mayonnaise. However, rather than buying the mayonnaise, you could reuse the jar you have in the refrigerator (after checking the expiration date) or you could decide to make the mayonnaise after buying salt, vinegar, lemon juice, oil and eggs. Rather than buying the eggs, you could buy a chicken and … The point is, almost all make-reuse-buy decisions end up with the decision to buy at some level.
MIL-STD 499 said the way to design a system was to do functional decomposition. Students used to...