ECE362– Principles of Design
The System Engineering Process
Systems
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Unit Overview
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The systems challenge
System concepts and terms
Diagrams for systems
Actors, boundaries, interfaces
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>>The Systems Challenge<<
The Man-Made World Is Increasingly Populated by Systems
• Transportation, Energy & Power
Systems
• Manufacturing, Construction
Systems
• Telecommunication Networks
• Man-Made Biological, Health, and
Personal Care Systems
• Facility, Properties
• Business Processes
• Other Man-Made and Natural
Systems
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>>The Systems Challenge<<
These Systems Are Becoming More Complex
• Under pressure of demand & competition
• Enabled by progress in technology
• Becoming more complex at exponentially
growing rates
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>>The Systems Challenge<<
The Growth Of Systems Complexity Eventually Can Outpace
Human Ability To:
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Describe
Predict
Manage
Monitor
Configure
Evolve
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Understand
Install
Operate
Repair
Maintain
Account For
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Communicate About
Design and Implement
Manufacture
Diagnose
Control
Maintain Security Of
Those Systems must be produced . . .
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>>The Systems Challenge<<
. . . At Least Within Reasonable:
• Time
• Cost
• Effort
• Sense of Security from Risk
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Systematica Metaclass
The system perspective
• A System is a collection of interacting Components :
Interaction
Relationships
System
Components
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What does “interact” mean?
• Components are said to interact if one one component
can impact the state of another.
• Components that do not impact each others’ states are
said to be isolated or non-interacting.
Interacting
Interactions Impact
Component States
System
Non-interacting
Components
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What does “state” mean?
• The state of a component helps determine its externally
visible future interactive behavior.
• States are values of component state variables, such as:
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Temperature, Pressure, Density
Position, Velocity, Acceleration
Happiness, Frustration, Satisfaction
Profitability
Voltage, Current
Asleep, Awake
Empty, Full
Components and systems have states.
System
Components
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Systems may use any technology
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Mechanical
Electronic
Software
Chemical
Thermodynamic
Human organizations
Biological
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Example system
• System: Semi-trailer truck hauling freight
• Components: engine, power train, suspension,
lubrication system, fuel system, braking system,
electrical system, cab, trailer, navigation system,
communication system, software modules
• Interactions: mechanical support, electrical power
dependency, control interaction, mechanical drive,
thermal interaction
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Example system
• System: Telecommunication services system
• Components: telephones, modems, workstations,
transmission links, circuits, switches, base stations,
communication sessions, software, customer
requests, billing systems, customer analysts
• Interactions: electrical & optical physical
interactions, symbolic trunk status signaling,
mechanical mounting support, power dependency,
fault propagation
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Subsystems
• A Component can itself be a System
• This just means the Component has Components.
• This makes it a Subsystem of the first system.
• This can continue indefinitely.
• Where does it stop?
System
Subsystem
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Where does it stop?
• It does not stop — we do!
• These are modeling constructs—ideas in our heads.
• We are using the System Perspective:
• How we have chosen to think about a system.
System
Subsystem
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Is everything a system?
• Is a rock a system?
– Does it have parts? Interactions?
– If you are a geologist, a rock is a system:
• Strata, crystals, chemical interactions, pressures
– But, if you are using the rock in your slingshot,
this is not useful to know!
– Different people need different models for
different purposes
– Views of models
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What to model?
• In model based systems engineering, it is
not enough for a model to be correct:
– We also have to ask if a model is useful to us.
– We only need to model what is useful, to sort
out requirements, plan designs, communicate
specifications, verify behavior, etc.
– There is a tendency of new modelers to model
too much, to include too much detail …. so
watch out!
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The System Perspective
• Some definitions of the concept of system include not only:
– that there are components,
– and that there is a framework of interaction relationships,
• but also these additions:
– that a system exists for a purpose and has a body of rules about it.
Interaction
Relationships
System
Components
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The System Perspective
• Systematica formally models intelligence and the actual management
of systems, including both man-made and natural systems:
– So, we consider ideas such as “purpose” and “rules” to be part of other
(extended) systems that we will model later in this workshop, including use of
other Metaclasses.
– Thus, we only need to remember that a system is a collection of components and
their interaction relationships:
Interaction
Relationships
System
Components
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System diagrams
• Formal diagram notation:
– UML subset--UML class/object diagrams
• Frequently used system diagrams:
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System environment diagram
System domain diagram
System logical architecture diagram
System physical architecture diagram (physical
deployment diagram)
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System diagrams
• System environment diagram: To illustrate
the systems (called “actors”) outside a
“subject system”, with which it interacts.
• System domain diagram: To illustrate the
important relationships between the actors
for a subject system (domain knowledge).
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Actors, boundaries, interfaces
• Actors: The systems external to a subject system, with
which it directly interacts.
• System Boundaries: The set of all actors for a subject
system constitutes its formal boundary. This is often
informally illustrated with a line boundary dividing the
system from its environment:
Environment
System
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Actors, boundaries, interfaces
• System Interfaces: We will formally define
interfaces in a later unit, but show their
graphical appearance for now.
Interfaces
Environment
System
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States
• A State is a system condition, situation, or mode, that has
existence for a length of time. The state of a system
determines in part its future behavior.
• The time history of states of systems can be described using
“trajectories” of states:
– finite state machines, or
– continuous paths in phase space.
State transition diagrams, or
(UML) state charts, can be
used to graphically describe
finite state machines.
State B
causal event 1
causal event 2
State C
State A
causal event 3
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States
• State transitions are graphically illustrated links indicating
the passage of a system from one state to another.
• Events are occurrences in time.
• Events can be modeled as the cause of state transitions, by
labeling state transition lines with event names.
Event Name
State B
causal event 2
State Transition
causal event 1
State
State C
State A
causal event 3
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Lawn mower example
lawnmower started
Starting
Servicing
service complete
Idling
disengage mowing
service request
received
start request received
Shut Down
Normal Mowing
engage
mowing
shut down initiated
normal shut down completed
Shutting Down
overheat recovery complete
overheated shutdown completed
Overheat Recovering
Lawnmower State
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Organizing functions with states
• Functions can be associated with states.
– This is a way to indicate what functional
interactions are required to occur during certain
situations (that is, “when” they should occur in
time)
– This is a way to connect the (software
engineering) “use case method” to state and
function modeling techniques
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Lawnmower example
Starting
Functions:
1. Start (w/i 10 seconds of turning
key)
2.Check Starting Interlocks (blades
must be disengaged)
3. Noise control (conform to ASPE
102.3 noise guidelines)
4.Emission control (conform to EPA
11.2 emission guidelines)
Mowing
Functions:
1.Cut grass (to operator
determined length)
2. Noise control (conform
to ASPE 102.3 noise
guidelines)
4.Emission control
(conform to EPA 11.2
emission guidelines)
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Shutting Down
Functions:
1. Disengage blades
2. Shut down engine
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Systematica, Gestalt Rules, Return on Variation are trademarks of System Sciences, LLC.
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