(c) Bruce Powel Douglass, Ph.D. 2019

Mar 7, 2018

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What are your hot questions and systems engineering and MBSE?

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  • Hi! I am reading in Chapter 8 of Agile Systems Engineering, while simultaneously reviewing the example model TWrecks1.rpy and have some questions. in ibCommCoord there are three flowProperties called cmdProximalJointAngle:JointRadian cmdMedialJointAngle:JointRadian cmdDistalJointAngle:JointRadian These are combined into the message CommandedJointAngleMsg:CANMsg with the following mapping: Data0:unsigned char = Low byte Proximal Angle Data1:unsigned char = High byte Proximal Angle Data2:unsigned char = Low byte Medial Angle Data3:unsigned char = High byte Medial Angle Data4:unsigned char = Low byte Distal Angle Data5:unsigned char = High byte Distal Angle In paint it would look something like this: Now to my questions: Why are there no explicit relation between the logical flowProperties and the physical data? Wouldn't that kind of traceability be beneficial to know exactly how the logical data schema is refined into the physical? It feels unsatisfying on relying on the semantics of the text string to indicate traceability. If I where to add such a relation how would I do it in the best way? To I have tried to use «allocate» and «dependency» , but that can only be done between the interface specification and the flow property and not to the exact value (Data0, Data1, ...). See below: Thanks in advance! Best regards Markus
  • Suppose you have your system "S" that receives an event Ev1() and an operational contract called OP1(). During the architectural phase, you decide to fulfill the requirements with two blocks, B1 and B2. B1 receives Ev1(), but B2 is allocated the operational contract OP1(). Now between B1 and B2, a message is needed. I assume this is Ev1() again, it is just forwarded. However, I need them to be different, because it might be the case, that B1 performs some tasks on the parameters of Ev1() and then forwards the filtered data to B2. How would you model this? Do I need to invent a new message for this? I have seen in the examples in the paper from H. P. Hoffmann and the Harmony deskbook that the messages are just duplicated. I suppose Ev1() in the above example is duplicated but now has a different TYPE for its parameter. Afterall, the fact that I drew Ev1() from B1 to B2 has already created a new event on B2, so yes, they are different. For the example in Hoffmanns' paper see figure 10, the operational contract is reqCalcCmdrLosCmd, which is shown several times between LRUs: http://static1.1.sqspcdn.com/static/f/702523/9277834/1288929233000/200511-Hoffmann.pdf?token=F%2FmLJpHRBLG3JpdFzxeJcZZyB1I%3D
  • Dear Bruce, I have some problems with abstractions/ kinds of subsystems, especially with logical and physical. The reason is, that logical subsystems often map to multiple physical subsystems and a physical subsystem can contain multiple logical subsystems. In one of your SE book there is an example for physical subsystems. [...] For example, an automotive braking subsystem will contain mechanical (brake pedal, braking pads), hydraulic (pistons, o-rings, pump, fluid reservoir), electronic (ECU,2 pedal position, wiring), and software (ABS) components [...] (1) With this description, I would model an _subsystem and components view_ that has separate components ECU and software, even if the software do run on the ECU of course. I would show this relation in an separate view? What is necessary in Handout and is it an SE or SW task? It is always difficult for me to separate Systems Engineering from native downstream disciplines. (2) When I show logical subsystem, then it may be possible that a subsystem contains hydraulic, electric parts and SW. In a _deployment view_ I have to identify the engineering disciplines. Right? (3) Which possibilities can I use to show the relation of logical parts of deployment view and physical components? Thank you very much! Best regards Matthias