State Diagrams
PB007 Software Engineering I
Bruno Rossi
7. 11. 2016
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State Diagrams
The State Diagram models the dynamic behavior (life cycle) of one
reactive object (class, use case, system, subsystem).
Its essential components are:
States
Transitions
Events
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The components of a state diagram
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State
The State represents a semantically important situation in which the
object can be. It is generally determined by the value of attributes,
relations with other objects, and activities performed.
Conditions may include:
Entry/Exit actions
Internal transitions/actions
Internal activities
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Transitions
Transitions define how you will get from one state to another.
The transition elements:
Events
Conditions
Actions
Syntax: event[guard condition]/action
Semantics: At the occurence of the event, and with condition satisfied,
perform action and go to the new state.
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Events
Events are the stimulus to which the subject may react by changing the
status or performing some kind of operation. .
We distinguish 4 types of events:
Call event - calling the operations of an object.
Signal event - asynchronous emission and reception of signals from
one object to another.
Change event - truth expression. The event occurs after you change
its value from false to true.
Time event - events occur at a certain time (when()) or after a
certain time (after())
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Events - examples
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Composite state
Composite states are states that have some nested conditions.
We distinguish two types of composite states:
Simple composite states - that are just in one area - they are
suitable to capture the inheritance aspects between different states.
Orthogonal composite states - that cover two or more areas. Each
of them contains a nested state diagram. Their execution is carried
out in parallel.
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Composite state - Example
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Composite state - Example II
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Additional Resources
http://www.uml-diagrams.org/state-machine-diagrams.html
http://mpavus.wz.cz/uml/uml-b-state-3-2-2.php
http://www.agilemodeling.com/artifacts/
stateMachineDiagram.htm
http://www.sparxsystems.com.au/resources/uml2_tutorial/
uml2_statediagram.html
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Tasks
Select one reactive object in your system that you will model with a
state diagram.
First, draw up a list of all the states that can be found in the object.
Select then those that are really interesting to discriminate with
respect to the features of the system.
Create a list of events (external stimuli) that cause interaction with
the object. From the list, select those that affect/alter the state of
the object.
On the basis of the lists of conditions and events, draw the state
diagram. Try to take advantage of inheritance between states and
thus simplifying the resulting model.
Upload the PDF report into the folder for (Week 07).
Deadline: Friday, 11.11.16 23:59
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Customization of PDF Export
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