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Sequentially Constructive Charts (SCCharts)

 

SCCharts [5] is a new visual synchronous language that is designed for specifying safety-critical reactive systems. SCCharts uses a new statechart notation similar to Harel Statecharts [3] and provides deterministic concurrency based on a synchronous model of computation (MoC), without restrictions common to previous synchronous MoCs like the Esterel constructive semantics [2].  Specifically, we lift earlier limitations on sequential accesses to shared variables, by leveraging the sequentially constructive MoC [4]. Thus SCCharts in short are SyncCharts [1] syntax plus Sequentially Constructive semantics.

The key features of SCCharts are defined by a very small set of elements, the Core SCCharts, consisting of state machines plus fork/join concurrency.

Conversely, Extended SCCharts contain a rich set of advanced features, such as different abort types, signals, history transitions, etc., all of which can be reduced via semantics preserving model-to-model (M2M) transformations into Core SCCharts. Extended SCCharts features are syntactic sugar because they can be expressed by a combination of Core SCCharts features.

...

A core SCChart is composed of elements of a minimal set of constructs. Additional constructs and syntactical sugar (f.e. actions, suspend) are introduced in extended SCCharts. Every extended SCCharts can be transformed into a core SCChart.

 

Core SCChartExtended SCChartsGraphical comparison
  • Simple States
  • Hierarchical States
    (aka Composite States)
  • Regions
  • Transitions (weak abort)
  • Immediate Transitions
  • Normal Termination 
  • Variables (primitive types)
  • Interface Declaration

 

Core SCCharts +

  • Connector (aka Choice)
  • Strong Abort
  • Weak Abort
  • History Transition
  • Suspension
  • Entry Action
  • During Action (aka Inner Action)
  • Exit Action
  • Signal
  • Pre
  • Count Delay
  • Conditional Termination
  • Initialization
  • Complex Final State
  • Deferred Transition

Image Modified

[click to enlarge]

Modeling & Compiling SCCharts

SCCharts can be modeled using our KIELER SCChrats editor and compiler (download). The modeling editor is a textual editor based on the itemis Xtext framework. The language used to model SCCharts textually is called SCT and documented here. A quick start guide introducing first steps from downloading over modeling to compiling SCCharts can be found here.

Project Status

Subproject/ExtensionProgress Released
SCCharts Editor (*.sct)Implemented and tested 0.9.0
SCG EditorImplemented and tested 0.9.0
SCL EditorImplementation not yet finished 

planned for 0.11.0

Extended 2 Core SCChartsImplemented, not yet fully tested 0.9.0
Core 2 Normalized SCChartsImplemented, not yet fully tested (some known bugs) 0.9.0
Normalized SCCharts 2 SCGImplemented, not yet fully tested (some known bugs) 0.9.0
SCG 2 Sequential SCG

Implemented and partly tested,

straightforward scheduler for 0.9.0 release,

enhanced scheduler planned for 0.10.0 release.

 0.9.0
SCG 2 C

Implemented by transformation via common S language

(this can also be translated into Java -> SJL)

 0.9.0
Online Compiler and Command Line ToolsFinished, available in nightly build planned for 0.10.0
SimulationA full featured simulation is currently being developed planned for 0.10.0

 

Known Limitations

  • Normalization may result in conditions where there actually is no conditions, this should optimized manually
  • SCG Generation currently produces unoptimized hierarchy levels, e.g., fork nodes with just one successor node should be eliminated
  • Scheduling of unconnected SCG exit nodes is currently not possible