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Henshin/Units

< Henshin
Revision as of 05:57, 6 March 2018 by Heidelme.students.uni-marburg.de (Talk | contribs) (Conditional Unit: Correct mistake in 'Execution successful if:')

In Henshin, control flow is specified using units. Units have a fixed number of sub-units, allowing for arbitrary nesting. This article describes the available units.

Units can be categorized in two groups by their possible number of sub-units. For unary units the number of possible sub-units is fixed. Multi-units have an arbitrary number of sub-units.

All units at some point check the executability of a sub-unit. This check means the sub-unit is executed.

Usage

Unit creation in graphical editor

Create unit

To add a unit to a Henshin project in the graphical editor, first open the *.henshin_diagram file. Then select Unit from the Palette on the right of the window. Afterwards left-click any empty space of the Henshin diagram and choose the desired unit from the appearing menu.

Add sub-unit

If the selected unit is a Multi-Unit, some sub-units have to be added manually. Therefore select Invocation from the Palette and click on the according Multi-Unit. Then type the name of the desired rule or unit.

Unit creation in tree-based editor

To add a unit to a Henshin project in the tree-based editor, first open the *.henshin file. Then right-click on the parent Module. Select New Child and afterwards the desired unit from the context menu. After creation the units can be edited in their Properties view.

Henshin Units Creation TreeEditor.png

Multi-Units

Sequential Unit

Henshin Sequential Unit.png
  • Number of sub-units: arbitrary (0..*)
  • Available Flags/Properties: strict, rollback (both of type boolean)
  • Execution successful if:
    • strict=true: all sub-units successful or no sub-units existing
    • strict=false: at least one sub-unit successful or no sub-units existing
  • Control flow: The sub-units are executed in the given order.
    • strict=false, rollback=true/false: If one of the sub-units cannot be executed, the next sub-unit is executed. As the execution never stops, the rollback flag has no effect.
    • strict=true, rollback=false: If one of the sub-units cannot be executed, the execution stops.
    • strict=true, rollback=true: If one of the sub-units cannot be executed, the execution stops and previous executions are reverted.

Priority Unit

Henshin Priority Unit.png
  • Number of sub-units: arbitrary (0..*)
  • Available Flags/Properties: none
  • Execution successful if: one sub-unit successful (Empty priority units always fail.)
  • Control flow: The sub-units are checked in the given order for executability. The first sub-unit found to be executable is executed.

Independent Unit

Henshin Independent Unit.png
  • Number of sub-units: arbitrary (0..*)
  • Available Flags/Properties: none
  • Execution successful: one sub-unit succesful (Empty independent units always fail.)
  • Control flow: The sub-units are checked in nondeterministic order for executability. The first sub-unit found to be executable is executed.

Unary Units

Loop Unit

Henshin Loop Unit.png
  • Number of sub-units: 1
  • Available Flags/Properties: none
  • Execution successful: always
  • Control flow: The sub-unit is executed as often as it is executable.

Iterated Unit

Henshin Iterated Unit.png
  • Number of sub-units: 1
  • Available Flags/Properties: iterations (integer), strict, rollback (both of type boolean)
  • Execution successful if:
    • strict=true: all iterations successful
    • strict=false: at least one iteration successful
  • Control flow: The sub-unit is executed as often as specified in the iterations property.
    • strict=false, rollback=true/false: If one of the iterations cannot be executed, the next iteration is executed. As the execution never stops, the rollback flag has no effect.
    • strict=true, rollback=false: If one of the iterations cannot be executed, the execution stops.
    • strict=true, rollback=true: If one of the iterations cannot be executed, the execution stops and previous executions are reverted.

Conditional Unit

Henshin Conditional Unit.png
  • Number of sub-units: 2 or 3
  • Available Flags/Properties: none
  • Execution successful if: if unit and then unit are successful or if unit is unsuccessful while else unit is successful or not present.
  • Control flow: If a match for the if unit can be found, the then unit is executed. Otherwise, if present, the else unit is executed.

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