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Les,
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<div><i>“When I use a word, it means just what I choose it to mean — neither more nor less.”</i></div>
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<div>I would say that’s fine so long as the chosen meanings are out in the open. If someone has openly defined what “unptyfratz” means to them then they should be able to use that term in a way consistent with that open definition. One clear problem is when
the speaker’s meaning has not been openly defined. In that case, all the listener can do is to assume a definition, probably one that’s the same or close to their own definition of that same word (assuming one exists). Another clear problem is when the speaker
uses the word inconsistent with the definition they provided.</div>
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<div><i>“Steve, I am interested in how you would explain the concept of state and state engine to a plant operator. Back in the day, my colleagues and I had great success using “step” and “sequence control unit.””</i></div>
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<div>If it’s a face-to-face conversation, I don’t see a problem with meeting the others more than half way. If they have pre-existing notions about what certain words mean, then part of the time will be spent looking at the named concept, e.g., “state” and
“event”, providing my definitions—and examples—of those terms, and then asking if they use different words to mean the same or similar things. Once we are able to work out the clear relationship between their use of words and my use of words we can push forward.</div>
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<div>My target audience has not traditionally been Subject Matter Experts like Plant Operators, more often I work with the software developers and/or the so-called “Business Analysts” in teaching them how to develop models that include Finite Automata. That
said, I have worked with Subject Matter Experts, but not in the capacity of teaching them how to build the models themselves, rather in teaching them enough that they can interpret the models and tell if the as-written model is a correct representation of
their “business” (i.e., the abstract process they want software to automate).</div>
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<div>When it’s not face-to-face, then the immediate feedback loop is missing. So it becomes even more important to provide written, as precise as possible definitions, and give a lot of examples. If you want to see how I do that when teaching developers and
Business Analysts, feel free to check out Chapter 10 in my book, “How to Engineer Software”. That entire chapter is on the topic of Finite Automata / Finite State Machine modeling. You might also want or need to check out Appendix L which (hopefully) precisely
defines the semantics of the modeling language I use. FYI, Appendix L is at least in part driven by an interesting paper I read many years ago:</div>
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<div>von der Beeck, M. (1994). A comparison of Statecharts variants. In <i>Formal Techniques in Real-Time and Fault-Tolerant Systems</i> (pp. 128–148). Springer Berlin Heidelberg.</div>
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<div>The problem von der Beeck highlights is precisely weaknesses in Statechart semantics. He identifies 19 semantically significant variations in how Statecharts can be interpreted. Insofar as UML imports Harel’s Statecharts pretty much as-is, UML has semantic
holes in it large enough to sail supertankers through. There’s a mechanism in UML called “Profile” that’s there because Steve Mellor and I put it there. The vast majority of the UML committee was perfectly happy with horribly weakly-defined modeling semantics
because “they didn’t want to force people into doing things in any one specific way”. Both Steve Mellor and I—partly using the von der Beeck paper—pointed out the implications of ambiguous interpretations of models in safety- and mission-critical systems (I
was working at Rockwell Collins Avionics at the time). Profiles were added to UML as a means to allow someone to more precisely define how they expected their model to be interpreted, i.e., their precise and intended definitions of the modeling concepts they
were using. In fact, Appendix L is largely the UML Profile that (hopefully) precisely defines the modeling semantics for a UML model of the modeling language.</div>
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<div>To be truly useful for software development, a model such as a State Model must have one, only one, and exactly one interpretation to all readers.</div>
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<div>— steve</div>
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<div>On May 20, 2026, at 2:19 AM, Les Chambers <les@chambers.com.au> wrote:</div>
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<span class="gmail-s1" style="font-kerning:none">My apologies, all.<span class="gmail-Apple-converted-space"> </span></span></div>
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<span class="gmail-s1" style="font-kerning:none">In my naivete, I've opened a can of worms. It turns out the systems engineering profession has collectively fallen down a rabbit hole with Alice and her adventures in Wonderland, and later Through the Looking
Glass, where she meets Humpty Dumpty, who by Fiat announces, “</span><span class="gmail-s2" style="font-kerning:none;background-color:rgb(249,246,242)">When I use a word, it means just what I choose it to mean — neither more nor less.”</span></div>
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<span class="gmail-s1" style="font-kerning:none">This is pretty much where we stand. If you enjoy a good laugh, continue reading my dialogue with Gemini here:</span></div>
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<span class="gmail-s1" style="font-kerning:none"><a href="https://bit.ly/3RPoHTg">https://bit.ly/3RPoHTg</a></span></div>
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<span class="gmail-s3" style="font-kerning:none;color:rgb(29,28,23);background-color:rgb(249,246,242)">Scroll down to my prompt,
</span><span class="gmail-s4" style="font-kerning:none">“</span><span class="gmail-s1" style="font-kerning:none">Do IEC 61508 and EN 50128 refer to states or modes or both” and read on.</span></div>
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<span class="gmail-s1" style="font-kerning:none">As you scroll through the pronouncements of the IEC, CENELEC, US DoD and finally the IEEE (Gasp! -
</span><span class="gmail-s5" style="font-kerning:none;color:rgb(10,10,10)"><b>O Captain! my Captain!)</b></span><span class="gmail-s1" style="font-kerning:none">. You may reach my conclusion that this is an omelette that cannot be unscrambled. You might as
well demand the Americans put the U back in color (a righteous though futile </span>
<span class="gmail-s5" style="font-kerning:none;color:rgb(10,10,10)"><b>Don Quixote-like
</b></span><span class="gmail-s1" style="font-kerning:none">mission - so easily led those guys; Noah Webster says, "I pulled it out for simplicity", and no one complains?)</span></div>
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<span class="gmail-s1" style="font-kerning:none">All I can say before I ride off to tilt at other windmills:</span></div>
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<span class="gmail-s1" style="font-kerning:none">1. PBL, you have my blessing to call a mode a mode along with millions of other pilots in the world; while we, in our subset of chemical processing control systems practitioners, will continue to colloquialize
“step” for state and “sequence control unit” for state engine. Let's not mess with anything that works.</span></div>
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<span class="gmail-s1" style="font-kerning:none">2. Phil, my humble suggestion is that you tell your students that the semantics of state and mode are a function of the application Domain. For example, if you land in DoD weapon systems, you'd better assume
the local mode lingo or be strung up by some hard-driving CAG.</span></div>
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<span class="gmail-s1" style="font-kerning:none">3. Steve, I am interested in how you would explain the concept of state and state engine to a plant operator. Back in the day, my colleagues and I had great success using “step” and “sequence control unit.” Not
once but hundreds of times in plants throughout the USA, Germany, the Netherlands, South America, Australia; across cultures, across languages; to an eclectic band of operators ranging from good old boys without a high school education to university graduates.</span></div>
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<span class="gmail-s1" style="font-kerning:none">My view is that the overarching issue here is cognition achieved through shared mental models and impedance matching. The operator must be part of, inside the boundary of, the scope of automation. The operator's
brain must share the mental model of the silicon. The sharing can only occur if there is a total impedance match between mentor and student as the model concept is passed. It turns out that at our most primal level, we human beings are pattern matchers. All
control rooms I ever inhabited had a simple state diagram, the defining pattern, pinned to the wall.</span></div>
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<span class="gmail-s1" style="font-kerning:none">Lastly, in the chemical processing context, we are able to use the state engine in all life cycle phases from requirements definition to implementation to operations. This was only possible because the plant
engineers wrote the programs and lived with the plant in operations. I had a hand in training some of these guys. Looking back, it is clear to me that there could be no ambiguity about the definition of state. It was a safety issue.<span class="gmail-Apple-converted-space"> </span></span></div>
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<span class="gmail-s1" style="font-kerning:none">So Phil, graduating engineers who go out into the world looking for states and modes as separate entities is wasting their brain cycles and a potential hazard.</span></div>
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<span class="gmail-s1" style="font-kerning:none"></span><br>
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<span class="gmail-s1" style="font-kerning:none">It's comforting that Gemini, sort of, agrees with me. I cite its conclusion if you scroll down to the bottom.</span></div>
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<span class="gmail-s1" style="font-kerning:none"><b>“The Verdict on Your Assertion</b></span></div>
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<span class="gmail-s1" style="font-kerning:none">Your assertion that the industry should "cease and desist" from using both terms is backed up by the IEEE's own documentation.</span></div>
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<span class="gmail-s1" style="font-kerning:none">If you look at the <b>IEEE definition of a Finite State Machine (FSM)</b>:</span></div>
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<span class="gmail-s1" style="font-kerning:none"><i>"A computational model consisting of a finite number of states and transitions between those states..."</i><i></i></span></div>
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<span class="gmail-s1" style="font-kerning:none">There is no mention of "modes" in the mathematics of state machines. Computer scientists and automation engineers using IEEE standards can completely specify, verify, and execute complex, safe system behaviors
using <i>only</i> states.</span></div>
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<span class="gmail-s1" style="font-kerning:none">The IEEE maintains "mode" in its vocabulary database not out of mathematical necessity, but out of
<b>legacy compliance</b>—purely to accommodate the operational, user-facing language used by pilots, drivers, and defense customers who want to see the word "Mode" on their control panels. Structurally, it remains a redundant concept.”</span></div>
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<span class="gmail-s1" style="font-kerning:none">Hallelujah brother. Praise the Lord and pass the specification!</span></div>
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<span class="gmail-s1" style="font-kerning:none">Les</span></div>
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<div dir="ltr" class="gmail_attr">On Wed, 20 May 2026 at 04:23, Steve Tockey <<a href="mailto:steve.tockey@construx.com">steve.tockey@construx.com</a>> wrote:<br>
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<div>I’ll stir the pot a bit more here, because it’s been an issue in what I’ve been facing over the years. That issue is the difference between the Finite Automata view of the word “state” vs. a purely mathematical, e.g., Abstract Data Type, view of that same
word.</div>
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<div>If we take as an example a mythical Bank Account. Data attributes of this mythical Bank Account class would include at least the following:</div>
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<div>.balance — how much money is held in the bank account right now</div>
<div>.overdraft limit — how much the account’s owners are allowed to let the balance go negative, i.e., a very short term loan</div>
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<div>In a Finite Automata view of the behavior of Bank Accounts, we might have the following UML Statechart:</div>
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<div><span id="cid:ii_19e44ada05c5b206ef61"><PastedGraphic-1.png></span></div>
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<div>Simple. Two states: Normal and Overdrawn. In the Normal state, the owners have full ability to deposit and withdraw so long as any one withdrawal does not allow the account balance to go below the negative of the overdraft limit. E.g, an account’s .balance
is 400.00 Euros, and the overdraft limit is 200.00 Euros. Any attempt to withdraw of between 0.01 Euro and 400.00 Euros would be allowed and leave the account in the Normal state. Any attempt to withdraw of between 400.01 Euros and 600.00 Euros would also
be allowed but would leave the account in the Overdrawn state. Any attempt to withdraw more than 600.00 Euros would be ignored. When the account is in the Overdrawn state, all requests to withdraw any amount are refused. In the Overdrawn state, only deposits
are allowed until the .balance is back to at least 0.00 Euros. So my point here is that in the Finite Automata view of the universe, “states” are defined in terms of the state-level responses that happen as a result of the events (and, possibly, event parameter
values). Whether the account’s .balance is 400.00 Euros or 4000.00 Euros, a request to withdraw 200.00 Euros will be treated the same way. Les’s view, and mine too.</div>
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<div>However, in the purely mathematical / Abstract Data Type view of the world, merely changing the .balance of the account from 400.00 Euros to 400.01 Euros changes its state. In the Abstract Data Type world, state is defined strictly by the properties and
values that make up the data. Because the .balance is a defining property of a bank account's state, accounts with different balances hold distinctly different states.</div>
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<div>This is not to say that those two views are fundamentally irreconcilable. The “States” in the Finite Automata world correspond directly to Equivalence Classes of “States” in the Abstract Data Type world where the responses to events in any Equivalene Class
are the same from a “response to the next event” perspective.</div>
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<div>So on the one hand, I’m agreeing with Les that there is a problem with how INCOSE views “state” and “mode”. On the other hand, I’m also pointing out that to the extent that pure math people get involved, the meaning of the word “state” itself becomes ambiguous
even if you completely outlaw the word “mode”.</div>
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<div>The bottom line is that if you want people to truly understand what you’re talking about, you need to precisely define your terms, and use those terms consistent with their definitions. Further, if there are two different terms, then there must be unique
and meaningfully different definitions of those different terms, particularly when those terms carry similar or overlapping meanings in common use. To do otherwise is sloppy and unprofessional.</div>
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<div>And, Les, for what it’s worth, to me the word “mode” means “the value that appears most frequently in the data set”. (Smile)</div>
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<div>— steve</div>
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<div>On May 19, 2026, at 2:14 AM, Les Chambers <<a href="mailto:les@chambers.com.au" target="_blank">les@chambers.com.au</a>> wrote:</div>
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<p>Agreed, mode confusion in aerospace is a lethal issue, and it’s exactly why I argue we need absolute semantic clarity in our engineering standards.</p>
<p>My grievance isn’t with the <i>colloquial</i> use of the word 'mode' by operators or pilots. My grievance is with INCOSE—a premier international systems engineering body—explicitly stating that a State and a Mode are
<i>different entities</i>, yet failing to provide a rigorous, structural definition to separate them.</p>
<p>If we are to assert that they are distinct architectural concepts, we should be able to define them by their attributes.</p>
<p>From a systems engineering and computer science perspective, a <b>State</b> is a well-defined condition of a system, governed by an internal data structure (variables, inputs, and history) that determines how it responds to a given set of inputs.</p>
<p>To help me bridge the gap between aerospace practice and rigorous systems modelling, how would you define the unique attributes of a
<b>Mode</b> versus a <b>State</b>?</p>
<ul>
<li>
<p>Where do their data attributes actually differ?</p>
</li><li>
<p>Is a 'mode' simply a higher-level abstraction (a 'super-state' or collection of sub-states, like an autopilot operational regime)? This is hard to justify as David Harel’s Statecharts (and subsequently UML/SysML) solved this decades ago without needing the
word "mode." They introduced <b>composite states</b> (states within states) and <b>
orthogonal/concurrent states</b> (parallel state machines I applied extensively in chemical processing).</p>
</li><li>
<p>Or does it possess fundamentally different behavioural properties that a classic finite state machine cannot capture?</p>
</li></ul>
<p>I contend that if a 'mode' can be entirely modelled, verified, and executed using standard state-engine logic, then introducing it as a fundamentally
<i>distinct entity</i> in a foundational handbook—without definition—only invites the very 'mode confusion' Sarter and Woods warned us about."</p>
<p>There is a path to the truth. I assert that modelling a State as an entity defined by system attributes, invariants, and relationships, will reveal that what the industry calls a "mode" is structurally identical to a state.<br>
<br>
Les</p>
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<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, 19 May 2026 at 17:10, Prof. Dr. Peter Bernard Ladkin <<a href="mailto:ladkin@causalis.com" target="_blank">ladkin@causalis.com</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
On 2026-05-19 09:03 , Les Chambers wrote:<br>
> My view is that the word "mode" needs to be banished from the face of the Earth!<br>
<br>
Modes are essential when talking about autopilots, and have been for 30 years, ever since "mode
<br>
confusion" was introduced in Woods and Sarter's analysis of A320 AP workings.<br>
<br>
PBL<br>
<br>
Prof. Dr. Peter Bernard Ladkin<br>
Causalis Limited/Causalis IngenieurGmbH, Bielefeld, Germany<br>
Tel: +49 (0)521 3 29 31 00<br>
<br>
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