Modeling Events in
Object-Process Methodology
and in Statecharts
Iris Reinhartz-Berger, Arnon Sturm, Dov Dori
Technion – Israel Institute of Technology
{ieiris@tx, sturm@tx, dori@ie}.technion.ac.il
Outline
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Motivation
Methods and Issues Examined
Event Expression Comparison
Event Implementation
Comparison and Summary
Motivation
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Complex systems are often reactive, i.e., they
continuously respond to external and internal
stimuli (events) and may have time
constraints.
When modeling such systems, the designer
should be able to determine the system's
behavior, as well as its flow of control.
System modeling methods must express this
action semantics in a way that is both formal
and intuitive.
Methods and Issues Examined
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We focus on two behavior oriented approaches:
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Statecharts – Harel’s extension of state machines, used in
UML
Object-Process Methodology – an integrated modeling
method that unifies the system function, structure, and behavior
within one frame of reference.
We examine:
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The types of supported events
How these event types are integrated into complete system
specifications
What are the potential implications on the code derived from
each method.
Comparison by Event Types 1/2
Statecharts
OPM
entered( s3 )
State
Entrance
s2
s1
do/ TriggeredProcess
S’ triggers Triggered Process when it enters s3.
State
Exit
Activity
Start
s1
s2
exited( s3 )
do/ TriggeredProcess
s1
started(Invoking Process)
S’ triggers Triggered Process when it exits s3.
s2
do/ TriggeredProcess
Invoking Process triggers Triggered Process
when it starts.
Activity
Stop
s1
stopped (Invoking Process)
s2
do/ TriggeredProcess
Invoking Process triggers Triggered Process
when it stops.
Comparison by Event Types 2/2
Statecharts
Condition
Fulfillment
s1
true( c )
OPM
s2
do/ TriggeredProcess
C triggers Triggered Process when it enters true.
Condition
Violation
External
Event
s1
false( c )
s2
do/ TriggeredProcess
C triggers Triggered Process when it enters false.
s1
Event
s2
do/ TriggeredProcess
Event Generator, which is environmental,
triggers Triggered Process.
State Change Event
State
Change
s
s1
s2
entered (s1) or entered (s2)
s'
do/ TriggeredProcess
S triggers Triggered Process when its state
changes.
Activity Timeout Event
Activity
Timeout
Invoking Process triggers Min Constraint Handling
when it lasts less than Tmin and
Max Constraint Handling when it lasts more than Tmax.
State Timeout Event
State
Timeout
S triggers Min Constraint Handling
when s1 lasts less than Tmin and
Max Constraint Handling when s1 lasts more than Tmax.
Reaction Timeout Event
Reaction
Timeout
Event Generator, which is environmental,
triggers Triggered Process with a reaction time of Tmin to Tmax.
If Triggered Process starts within less than Tmin then Min Constraint
Handling is triggered.
If Triggered Process does not start within Tmax then Min Constraint
Handling is triggered.
Event Implementation
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Similar concepts of Statecharts and OPM.
Event Generator, which is environmental,
triggers Triggered Process.
Activating Condition can be true or false.
Triggered Process occurs if Activating
Condition is true.
int eventGeneratorWrapper() {
int res = NOT_CONSUMED;
if (activatingCondition.getStatus()==true) {
triggeredProcess.activate();
res = CONSUMED;
}
return res;
}
Methods Comparison 1/2
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Where Does the Behavior Occur?
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In Statecharts the behavior occurs in the states.
In OPM the behavior is executed in the processes, which act
to change the states of objects.
State-Activity Coupling
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In Statecharts there is a clear coupling between a state of an
object and the activity performed within it, so it is easy to
detect the system behavior within a single state.
In OPM, system state may be a combination of several objects’
states, making it more difficult to detect the the system behavior
within a single state.
Since in Statecharts each object gets its own “chart” it is not
clear how the entire system state is modeled.
Methods Comparison 2/2
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Event Source
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In Statecharts it is difficult to follow the event sources.
In OPM, the event generating source is explicitly specified,
enabling the designer to trace the events associated with a
specific entity (object, state, or process).
Accessibility, Legibility, Expressivity
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In OPM, OPDs use less text and more graphics, and the
semantics is made clear by the corresponding natural OPL
sentence, an element that does not exist in Statecharts
Summary
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OPM's visual and textual representations
provide a means for expressing various event
types in a formal yet intuitive way, which
compares favorably with Statecharts.
OPM supports modeling aspects (other than
behavior) which are not modeled in the standalone version of Statecharts (e.g.,
communication between objects, system
structure, and architecture).