Statecharts and STATEMATE • Background and Motivation ...€¦ · Alarm III Wristwatch • Four...
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1 Statecharts and STATEMATE Presented by Darren Liccardo Stephanie Augsburger October 3, 2000 October 3, 2000 2 Outline • Background and Motivation for Statecharts • Statechart Concepts and Formalisms – Clustering and Refinement – Orthogonality: Independence and concurrency – Special entrances, states, and unclustering – Actions and activities – Semantics • Statechart Tool: STATEMATE October 3, 2000 3 Background: System Types • Classification: Transformational vs. Reactive – Transformational systems can be sufficiently specified by a function or input/output relation – Examples: Data Processing, Plant Control – Methods exist to manage complex transformational systems – Supported by languages and implemented tools that perform well in practice October 3, 2000 4 Complex Reactive Systems • Event driven by – external and internal stimuli • System behavior: – Set of allowed input sequences and output events, conditions, and actions • Hard to formulate clear levels of abstraction • Difficult to describe in a clear and realistic, yet formal and rigorous manner • Examples
Transcript of Statecharts and STATEMATE • Background and Motivation ...€¦ · Alarm III Wristwatch • Four...
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Statecharts and STATEMATE
Presented by
Darren Liccardo
Stephanie Augsburger
October 3, 2000
October 3, 2000 2
Outline
• Background and Motivation for Statecharts
• Statechart Concepts and Formalisms– Clustering and Refinement
– Orthogonality: Independence and concurrency
– Special entrances, states, and unclustering
– Actions and activities
– Semantics
• Statechart Tool: STATEMATE
October 3, 2000 3
Background: System Types
• Classification: Transformational vs. Reactive– Transformational systems can be sufficiently specified
by a function or input/output relation
– Examples: Data Processing, Plant Control
– Methods exist to manage complex transformational systems
– Supported by languages and implemented tools that perform well in practice
October 3, 2000 4
Complex Reactive Systems
• Event driven by – external and internal stimuli
• System behavior: – Set of allowed input sequences and output events,
conditions, and actions
• Hard to formulate clear levels of abstraction• Difficult to describe in a clear and realistic, yet
formal and rigorous manner• Examples
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Automobiles
QuickTime™ and aSorenson Video decompressorare needed to see this picture.
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Cellular Phone
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Missiles, Avionics, and Space
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Motivation
• Goal: – Create a highly structured and economical
visual description language for dealing with complex reactive systems
• This formalism should be practical, yet rigorous enough to be amenable to detailed computer simulation
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Statechart Formalisms
A Precursor: Finite State Machines
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Finite State Machines
• Instantaneous– Transitions
– Assignments
– Transmission
• Time– Discrete
– Infinite
• Broadcasting of events
• event(condition)
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Practical Use of FSMs
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Finite State Machine Shortfalls
• Clustering states into a superstate:– “in all airborne states, when yellow handle is
pulled seat will be ejected”
• Independence and orthogonality – “gearbox change of state is independent of
braking system”
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Finite State Machine Shortfalls
• General transitions – “When selection button is pressed enter
selected mode.”
• Refinement of states– “display-mode consists of time-display, date-
display, and stopwatch-display”
Statechart Formalisms
A conceptual extension of FSMs
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Statecharts
• A visual formalism– Confront the shortfalls of finite state machines– Represent complex reactive systems
• Extension of finite state machines– Statecharts = state machines + depth +
orthogonality + broadcast-communication
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Running Example: Citizen Multi-Alarm III Wristwatch
• Four user buttons
• Can display time, date, and various setting
• Two alarms, hour chime
• stopwatch
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Clustering and Refinement
Adding depth to FSM
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XOR Composition
• If in state D, then in state A⊕C
• Superstate encapsulates commonalities of multiple states
• Generalized transitions– β transitions from any
state in superstate D
to state B
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Clustering and Refinement
• Design through abstraction– Clustering: A bottom up approach
– Refinement: A top down approach
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Refinement of displays state
displays
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Default Transitions
• Generalized entrances are ambiguous
Ride Control
Sport
Tour
α
γ
β
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History
• Revisit the last state that was left
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Equivalent Visualizations
• but be careful…
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Further Refinement of displays state
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Ambiguous Transitions
• Default contradiction
• γ is under specified
• α is over specified
Orthogonality
Adding Independence and concurrency to FSM
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AND Decomposition
• Superstate encapsulates– Concurrency (synchronization)
– Independence
• Natural representation of real systems
• Reduces exponential blowup of states to a linear semantics
• Transitions to and from orthogonal states
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AND Decomposition
• If in state Y, then in state A ^ D• A = B ⊕ C• D = E ⊕ F ⊕ G• Y =
(B⊕C)^(E⊕F⊕G)
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Exponential Blowup of States
• Exponential Enumeration of state Y
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Transitions to and from Orthogonal States
• Transitions may have multiple beginnings and ends
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Top Level Wristwatch
Other Features
Adding Special Entrances and Unclustering to FSM
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Other Features
• Special Entrances– Condition
– Selection
• Parameterized States
• Unclustering
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Conditional Entrances
• Same event, different conditions
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Selective Entrances
• Select state by event
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Parameterized States
• Collapse a uniform state structure
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Unclustering
• Abstraction navigation• Complexity
Management
Actions and Activities
Specifying Mealy Machine Behavior for statecharts
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Transitions with Actions
• Mealy machine output
• Transition Label– Event(condition)/action
• The action is carried out when the event takes place in the presence of the condition.
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States with Activities
• Activities take nonzero time
• Associated Actions– Start(activity)
– Stop(activity)
• Associated Condition– Active(activity)
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Actions and Activities
• State instructions: entry, exit, throughout Statechart Semantics
Ambiguities and formal representations of statecharts
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Semantic Ambiguities
• Recursive charts
• Probabilistic charts (Markov Model)
• Broadcast communication
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Formal Representation
• State tree (directed graph)
• Set of transitions– Ordered pair of configurations (source, target)
– Event(condition)/action
– Default and History
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Summing it all up
• Reactive Systems require special approaches
• Need for clear and rigorous behavioral description
• Statecharts are one possible formalism for specifying reactive behavior
• Future is visual languages, an example of which is STATEMATE…
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STATEMATE
StatemateStephanie
