System Thinking Approach in Writting Aircraft Design Requirements
System Thinking Approach in Writting Aircraft Design Requirements
(OP)
Hello,
I am currently pursuing a course degree in System engineering and I am a designer and aircraft engine performance analyst by profession.
Capturing the customer requirement is a critical issue in developing the right design specification for the system under context. There are tools currently available in Requirement engineering discipline where people from different background try to "teach how the system should work" to the designer. The tools are mainly SySML, UML, FFD and so on. From my point of view these tools are not very effective in bringing out the physical laws governing the system function. As a result, the function so developed or defined using these tools misleads the designer and hence the design.
I'd like to know the comments or remarks from other designer in Requirement management field about these tools and is there a best way to express the top-level functional requirements of the system?
Thank you
I am currently pursuing a course degree in System engineering and I am a designer and aircraft engine performance analyst by profession.
Capturing the customer requirement is a critical issue in developing the right design specification for the system under context. There are tools currently available in Requirement engineering discipline where people from different background try to "teach how the system should work" to the designer. The tools are mainly SySML, UML, FFD and so on. From my point of view these tools are not very effective in bringing out the physical laws governing the system function. As a result, the function so developed or defined using these tools misleads the designer and hence the design.
I'd like to know the comments or remarks from other designer in Requirement management field about these tools and is there a best way to express the top-level functional requirements of the system?
Thank you





RE: System Thinking Approach in Writting Aircraft Design Requirements
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RE: System Thinking Approach in Writting Aircraft Design Requirements
The general consensus is, there is no one single tool that could satisfy all the stakeholders in the loop. For a customer it doesn't matter how does it work and it is important for a designer to know how innovative work can add value to the business core value. Taking about innovation or quality that works depends on how the design requirements are formulated. It is a purely team wide mental acitivity wherein a good quality ideas forge in. So we need a standard process flow activity in sequence to tap the hidden decisive design parameters. By STANDARD I mean common to all the system and I think one way to investigate is to understand the behavioral aspects of the system (PATTERN). If there is standard design pattern rules, then writting a realistic and meaningful requirement could be as simple as possible.
Do you agree this?
thank you
RE: System Thinking Approach in Writting Aircraft Design Requirements
"there is no one single tool that could satisfy all the stakeholders in the loop. For a customer it doesn't matter how does it work and it is important for a designer to know how innovative work can add value to the business core value. Taking about innovation or quality that works depends on how the design requirements are formulated. It is a purely team wide mental activity wherein a good quality ideas forge in. So we need a standard process flow activity in sequence to tap the hidden decisive design parameters. By STANDARD I mean common to all the system and I think one way to investigate is to understand the behavioral aspects of the system (PATTERN). If there is standard design pattern rules, then writing a realistic and meaningful requirement could be as simple as possible."
just sound like management gobbledygook BS? Is this some sort of exercise to see how many buzzwords and management fad terms can be crammed into a single paragraph? or do systems engineers always talk like this?
RE: System Thinking Approach in Writting Aircraft Design Requirements
RE: System Thinking Approach in Writting Aircraft Design Requirements
RE: System Thinking Approach in Writting Aircraft Design Requirements
The reality is that 99.9% of the UML-based systems engineering effort is expended on that 10% of the specification, since those requirements are actually what UML was designed to express, e.g., "The system shall perform system initialization followed by asynchronous generation of SysReady within 30 seconds of application of power."
For my company, it's the other 90% of the system where innovation occurs.
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RE: System Thinking Approach in Writting Aircraft Design Requirements
Per se, the design solution space should not be restricted via through this requirement. We need physics based models to assess the pros and cons of our decision so as to avoid needless functional requirement. Again, it is not a question of reinventing the wheel, it is a quest to find the better way to express, design and implement. At requirement level definition as you rightly stated, we don't have a proper tool to look at the problem in a big picture neither an answer. In fact, this has turned my attention very deeply and now investigating the psychological aspects of the system
RE: System Thinking Approach in Writting Aircraft Design Requirements
I doubt any formal one size fits all process can really handle the first step.
The second relies on an experienced project team, not a piece of software.
Cheers
Greg Locock
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RE: System Thinking Approach in Writting Aircraft Design Requirements
A window has a "function" in ordinary English, but it, by itself, is purely a passive element, which is not something that is dealt well with UML, so it's not a "function" in UML. In fact, all the requirements that describe a window are more precisely defined as "properties" rather than functions. You cannot devolve "the paint shall be battleship gray" into a "function" and do stuff with it in a functional description language universe.
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RE: System Thinking Approach in Writting Aircraft Design Requirements
Well, this is a never-ending process. The beauty of system engineering is, I like the concept of system thinking wherein we identify the rationale from the need to functional system requirement full stop.As an example say window is a system and has a property like color, dimension, material, shape, layout and so on. It depends on entity like paint,human resources, some standards, ergonomics and so on. This will lead to innovation if one considers to have a window that shall be removable. From here we move into detailed specification, which is the job of domain expert & designer, with performance measures and identify its interface, RAMS after some trade-off analysis.
How we think is how we learn, communicate and implement. The designer mind is fused with lot of design alternatives and tools like UML, SysML certainly restricts their design solution space. I am not sure about the fact that these tools are the only way to communicate to the customer in a plain simple english lanaguage showing them the sequence of use cases. For me techniques like QFD and TRIZ are very interesting. Currently, the questions is how the system engineer can help the designer to write the right design specification? My answer to them was talk to the designer before writing the system requirement and you are fortunate if they have moment to spare.
RE: System Thinking Approach in Writting Aircraft Design Requirements
That's often the case. A solid, air tigght requirement would take a paragraph, but is often expressed as a single sentence. Nonetheless, most requirements analysis tools are "functional," because they are invariably written by computer scientists or mathematicians. The general purpose requirements tools like DOORS, only bookkeep requirements, and don't even begin to deal with requirements analysis and decomposition.
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RE: System Thinking Approach in Writting Aircraft Design Requirements
The reality is that for most projects the customer requirements are a whole mishmash of prior history, actual specific wants, and vague wishy washy desires. Capturing the prior history and experience is the most boring and most essential part of the process in my opinion. Otherwise you'll make exactly the same mistake as the previous project.
Cheers
Greg Locock
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RE: System Thinking Approach in Writting Aircraft Design Requirements
The attachment has something to say!!!
RE: System Thinking Approach in Writting Aircraft Design Requirements
MBSE is merely a slightly more formalized description of things that we already do, as embodied in ANSI632 or IEEE12207 or DoD-SEF or MSFC HDBK-1912. The concept of doing requirements analysis and modelling is embodied in every systems engineering process manual that I've ever had to slog through for the last 20 years.
And, as demonstrated in Figure 3-2 of your citation, the basic paradigm of the PMTE modelling is action/reaction, which does not address system "properties," which is often a sizable portion of a system's requirements specification. Moreover, while these PMTE tools are "vendor neutral," they are not model neutral, i.e., I can't arbitrarily plug in my model for laser rangefinder performance because there isn't even an input for something like that.
Even in Telelogic's flagship requirements management tool, DOORS, the typical contract and user actually use less than 10% of the capability and scope of the tool. This is particularly even more difficult when different revisions of DOORS are nearly completely incompatible with each other. DOORS cannot readily take the output from my performance simulation tools and incorporate them into the requirements management and tracking, because there really is no simple model for addressing performance requirements that are affected by the environmental requirements. The basic modelling tools don't even exist, and one would have to roll their own, because the amount of money invested in the development of such tools would make them proprietary.
As for certifications, organizations certified at CMMI 5, which is the highest achieveable level, do not, at the everyday organizational level, come close to adhering to their alleged capability maturity level. I know this because we've dealt with two companies with CMMI 5 certifications, and in both cases, their processes were actually no better than ours, with our measly CMM 3 certification.
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RE: System Thinking Approach in Writting Aircraft Design Requirements
My current work is to find an approach that allows the design synthesis to be a part of the SE process.
Well, requirements appear in different facets and there should be a method to determine the system behavior. We first need requirement decomposition as a classification of performance requirements, for sure. If we are talking about the aircraft weight then it can be decomposed by assigning weights to different modules (partionable) and this is different from a requirement which is very specific like engine weight (allocable). And if the requirement is about range then the decomposition process becomes computationally intensive (non-allocable) because it is the interaction of many properties like noise margin, threshold Signal-to Noise ratio and so on. It depends on the level of abstraction that we are handling.
If for the functionality of the system is examined, for example the fuselage has a property relating to the number of passengers it can carry and its shape is determined by the mission statement or higher level requirement. Its lower constituent's sub-systems like barrel segment, floor beams, bulkheads, skin stiffener element do not exhibit this capability on their own. Similarly, the geometry of the wing and nacelle are affected by the engine choice. At a conceptual level, it is just a 2D model not 3D so that we can play around the design solution space.
My concern is, the traditional SE tools creates a stasis in design process via a sequence of formal definition which carries nothing for a designer and you made it clear. I have to stick to the rules and assess how these tools can improve the problem definition or perhaps come out with a technique like TRIZ!!!
Thanks for sharing your insights.
RE: System Thinking Approach in Writting Aircraft Design Requirements
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: System Thinking Approach in Writting Aircraft Design Requirements
Thank you for the support
RE: System Thinking Approach in Writting Aircraft Design Requirements
The difficult thing, IMHO, is solving the problem, ie designing the solution. part of this difficulty is many of the design requirements are conflicting, or at least need a trade off to get to the "optimal" solution; consider weight vs cost, consider material cost vs manufacturing cost.
going back to your simple example of a window, the design spec will say at least weight, cost, and size (and maybe things like optical properties/distorsion, abrasion, ...). with weight and cost there'll be hard targets, but soft targets (benefits (profits) if you get lower than the target, penalties if you exceed them ... if it's 1 lb heavy we'll charge you $10, but being 1 lb heavier makes it $20 cheaper for you to make, and being a good partner you'll pocket the $10 you made).
Then you mentioned a removable window ... a whole different problem to define and to solve ...
RE: System Thinking Approach in Writting Aircraft Design Requirements
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RE: System Thinking Approach in Writting Aircraft Design Requirements
RE: System Thinking Approach in Writting Aircraft Design Requirements
RE: System Thinking Approach in Writting Aircraft Design Requirements
We used to have a whole seminar at my previous employer just on how to parse formal requirements.
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RE: System Thinking Approach in Writting Aircraft Design Requirements
1-----> customer needs
2 --->formal requirements(contains "shall" statment)
3----->Technical or design requirements (contains functional, performance, special quality....attributes)
4 ----> Design Specification.
RE: System Thinking Approach in Writting Aircraft Design Requirements
1 customer expectations
> project and enterprise external constraints
> operational scenarios
> measures of effectiveness
> system boundaries and interfaces
> utilization environments
> life-cycle process
> top level functional requirements/analysis
> performance requirements/analysis
> modes of operation
> technical performance measures
> design characteristics
> human factors
2 requirements baseline
> specification interpretation
> compare against customer expectations
> compare against constraints
> identify and reconcile variances and conflicts
> validate requirements
System Requirements Review
Your mileage may vary; not all projects require every step.
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RE: System Thinking Approach in Writting Aircraft Design Requirements
Thank you very much.
RE: System Thinking Approach in Writting Aircraft Design Requirements
Very few organizations can stand to spend that much up front, particularly when there's a standing army of designers chomping at the bit to start design.
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RE: System Thinking Approach in Writting Aircraft Design Requirements
Thank you once again
RE: System Thinking Approach in Writting Aircraft Design Requirements
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RE: System Thinking Approach in Writting Aircraft Design Requirements
Some concerns on emergent behavior of the system, is there a way to capture the strong and weak emergence properties of the system?
RE: System Thinking Approach in Writting Aircraft Design Requirements
Obviously, some properties are somewhere on the spectrum, and the systems engineer or designer must trade off against desirable properties that decrease when the undesirable properties also decrease. Ultimately, that trade shows up as an explicit requirement, or as a design decision.
Our SE group is fond of, but not always remembering to, developing design decision memos, which explicitly state, outside of the requirements, what design decisions were made, and their rationales. Additionally, some of that might be captured in the specification interpretation document, because the specifications are either unclear, ambiguous, or just plain silent.
Since my organization often gets formal, written requirements from the customer, we must often create SIDs to capture our understanding of what is often a woefully inadequate or incomplete or unclear specification from that customer. You may ask why the customer wouldn't simply change the requirement when confronted with obvious inadequacies or outright errors? That may be for reasons of extremely long signature/decision cycles or simple politics.
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RE: System Thinking Approach in Writting Aircraft Design Requirements
With simple techniques defined for each step, it took almost 10 days to complete the job partially and it is still in the process. And this is for a very simple system and indeed painstaking. Your points will aid me further down.
Thank you so much