This language thing can be tricky, and on some days, downright frustrating. The particular quirk of language that is the object of my strife today is that most every word has more than one meaning. In order to discern the intended meaning of a speaker/author, the context in which the word is used becomes critical. And to make matters even worse, science gets its geeky little hands on a word and gives it event more definitions!
Consider the word “external.” Dictonary.com lists 10 definitions! Three of those definitions are credited to fields of science. Yet none of them really tell us what external means in systems engineering.
Sometimes I like using this forum to share with you my reflections on recent support cases, and today that is my intention. I’ve had two calls in the last month where the meaning of external came in to play.
It seems too basic, right?
In systems engineering, an external is something outside the decomposition of the system. It’s commonly used to reference the interactions of your system with the elements in the systems context.
Most of my readers know this and may be wondering why I’m wandering down this trail.
The reality is, that as much as systems engineering attempts to define a “single version of the truth” or to be clear and unambiguous, it gave us two different uses of the same word!
When used on a block diagram, external has completely different meaning than when discussing your system as a whole. On the Physical Block and Interface Block diagrams, it simply means “not pictured here.” So, an element that may or may not be in the decomposition of an element in the view will be depicted on a block diagram as external if it has a direct relationship (relevant to the view) to one of the elements in the view. Being in the decomposition of an element in the view is not a factor here.
It’s a lot like the high school yearbook. You miss the one day where your team has their yearbook picture taken, and you’re not in. Instead, in the caption, you are “not pictured here.” You have a direct relationship to the people pictured, but you aren’t.
In a discipline where clarity of language is key to our success, it’s critical that we be aware of this dual meaning. Our field does emphasize singularity of meaning and this is one of the extremely rare circumstances that there are two meanings.
