MECH 567 – Systems Architecture
“Behavioral Modeling in SysML”
Stephen Milton and Sandra Biedron
Stephen.Milton@colostate.edu , Sandra.Biedron@colostate.edu
(970) 491-8742
Introduction
SysML has three kinds of modeling abstractions: structural modeling, requirements
modeling and behavioral modeling. Last week we got an introduction to structural
modeling by doing some simple projects with the Block Definition Diagram.
This week, we will introduce the second type of SysML diagram, the behavioral
diagram. As shown in Figure 1, SysML contains 4 different types of behavioral diagram.
Any one of them can be appropriate depending on the type of modeling that one is
performing. Today we are going to demonstrate the State Machine Diagram as an exemplar
of the types of behavior that can be modeled using SysML.
Figure 1
As always, the authoritative reference for using SysML is entitled, “OMG Systems
Modeling Language (OMG SysML™).”
It is available for no cost at
http://www.omg.org/spec/SysML/1.3/. You are encouraged to use the language definition
document as the ultimate resource for this course.
Laboratory Learning Objectives
1. Learn SysML behavioral modeling concepts
2. Gain experience with state machine diagrams in SysML
3. Model systems’ behavior using SysML state machine diagrams
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Task 1 – Behavioral Modeling
SysML has 4 types of behavioral models. We will start out using the state machine
diagram. Any block that has behavior must have an associated state machine diagram. For
example, last laboratory, we designed the following block to describe the function of a
centrifuge. In this case, the swinging head centrifuge has some behavior that is
represented by the function angle(). To more fully describe the function of this block, we
can link the SysML block definition diagram to a behavioral diagram with the objective of
describing the behavior of the block in more detail.
Figure 2. Example Structural Model with Embedded Operations
There are many types of behavioral modeling that are available to systems
engineering including flow charts, state diagrams, flow diagrams, and state charts.
State Diagram
flow diagrams
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Flow chart
The most familiar functional model in SysML is called the State Machine Diagram
(SMD). The SMD is derived from the State chart type of diagram, which has some simple
rules that apply to SysML as well. The states are meant to represent either a:
 Condition – This might be the case if the state is an operating condition or
status (e.g. Emergency, Normal )
 Activity – This might be the case if the block is to perform some task (e.g.
Sound Alarm)
 Idling – The block is waiting for a signal or input (e.g. Event Driven Systems)
The block should only occupy a single state at a time (as per UML and SysML
definitions). The transitions between states are assumed to be performed instantaneously.
Task 2 – State Machine Diagram Definitions and Examples
As with the BDD structural diagram, SysML defines the entities that make up the
diagram. The meta model for the state machine diagram is shown in Figure 2. Reviewing
the makeup of the BDD, we can see:
The State Machine Diagram is made up of 1 or more
states and 0 or more transitions. The state has a variety of
specializations including final states, composite states, simple
states, and initial states. The transition is made up of events,
actions, and guard conditions…
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Figure 1. State Machine Diagram meta-model
A subset of the symbols that are used in State Machine Diagrams are shown in the
following diagrams:
Figure . Elements of a State Machine Diagram
Armed with this information, we can begin to model the behavior of systems using
state machine diagrams.
States may or may not have activities or actions associated with them, but any
activities or actions should correspond to the operations from the Block Definition
Diagram. The only way to go from one state to another is to cross a transition. Generally
transitions are assumed to take zero time, so your system is assumed to occupy one state at
any given time. Events and messages can be received from other state machine diagrams.
The initial and final states tell the SMD where to start and stop the evaluation of the
diagram. Guard conditions enable transitions when they are Boolean TRUE.
Here is an example State Machine Diagram for the function of a hybrid car, let’s read
it together.
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Task 3 – State Machine Diagram for Functional Modeling
Like always, when we start to develop these architecture diagrams, we should most
likely begin with pencil and paper.
We can start together by drawing the BDD and State Machine Diagram to describe
the function of logging into your computer.
Let’s put this State Machine Diagram into Visio.
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Task 3 – Homework
1) Read Chapter 1 and Chapter 3.5 of Holt and Perry, SysML for Systems
Engineering,
2008,
available
to
all
CSU
students
at:
http://discovery.library.colostate.edu/Record/.b40132456
2) Construct a ~7 entity block definition diagram (BDD) for a system of interest
to you. Make sure that there are actions associated with a few of the entities
in the BDD.
3) Construct the state machine diagram that goes along with your system to
construct a simple system model describing both structure and function. The
most important part of this exercise is to construct a STM that is consistent
with your BDD.
You may type directly into this document, please replace my name with yours in the
header. Due Feb 3th, 2014, 11:59pm, MST. Turn in by email to milton@engr.colostate.edu
and nihan@engr.colostate.edu using the subject line “567 HW2 – YourLastName” in pdf
format.
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