STATECHARTS

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STATECHARTS

• Visual Formalism for Complex Systems

Presented by Marjan Kotorcevik
David HAREL
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Important concepts

• Transformational system
• input/output system
• State diagram
• directed graph with nodes (states) and arrows
  (transitions)
• Reactive system
• event driven system (input/output,
  condition/action, timing constraints)
• Statechart
• visual way of describing states and transitions.
• allows modularity, concurrency, refinement and
  zoom.

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State levels
State diagram
Statechart
-cluster superstate D -replace two B arrows with
one
-zoom out
-zoom out
-D is default state from D and B
-A is default state from A and C
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Citizen quartz multi-alarm III watch
- transitions made with pressing of a - display
date with pressing of d
History of the system

- enter state last visited from G and F
- enter state last visited from A, B, C, D and E
- if state in G (choose default state), if state
in F (choose last visited)
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Citizen quartz multi-alarm III watch
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Orthogonality independence and concurrency
orthogonate
- Y is orthogonal (AND) product of A and D
zoom out
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Orthogonality in citizen watch
2-minute return to time from all displays
other than the stopwatch
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Orthogonality in citizen watchview 2
P1, P2 alarm1 enabled (alarm2 disabled T1
T2)
P alarm1 enabled alarm2 enabled T1 T2)
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Additional statechart features
-condition and selection entrances
-delays and timeouts (lower/upper bound)
-unclustering
condition
selection
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Actions and activities
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Possible extensions to the basic statechart
formalism
-parameterized states
-overlapping states
-temporal logic, recursion and probabilistic
Assertion language for statecharts
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Semantics of Statecharts

• Difficult to provide formalism
• error (default contradiction)
• orthogonal components
• events generated by actions
• events generated by the dynamics of statecharts
• allow general, internal and simultaneous events

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Semantics of Statecharts

• State tree and set of transitions
• nextstep(X,C,E)

full basic configuration
set of external conditions
set of simultaneous external events
X
next possible set of full basic configurations
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Other solutions to behavioral description of
reactive systems

• Peri nets
• Milners CCS
• Zaves approach
• ESTEREL programming language

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Strengths of statechart approach

• Direct relevance to the embedded software systems
• Introduction of and-state
• Nearly a complete composition of well structured
  tools and notations to describe multi behavioral
  systems with concurrent internal/external events,
  actions, and activities.
• Possibly extensible.
• Similarity to state diagrams and availability of
  direct reconstruction and reimplementation

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Weaknesses

• Still in area of research since 1986
• Difficulties in dealing with correctness and
  semantics in particular cases
• Out of box thinking without simultaneous support
  of programming language or text notations
• Do not include the notion of states taking a
  measured amount of time compared to timed CSP
• No notion of guards implemented by Douglass
  (1999)