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Henshin/Units

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Revision as of 07:04, 11 March 2018 by Heidelme.students.uni-marburg.de (Talk | contribs) (Conditional Unit: Add caption)

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 by their possible number of sub-units. For unary units the number of sub-units is exactly one. Multi-units have an arbitrary number of sub-units. The specific unit Conditional Unit has two or three sub-units.

Each unit checks the executability of at least one sub-unit, if a sub-unit exists. 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. Currently every sub-unit is inserted behind all existing sub-units, which is especially relevant for PriorityUnits and SequentialUnits. If that's not the desired behaviour it is recommended to use the Properties view or the tree-based editor for sub-unit insertion or reordering.

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

Unary Units

A Unary Unit has exactly one sub-unit.

Loop Unit

Apply A as often as possible
  • 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.
  • Examples: Java2StateMachine, Ecore2Genmodel

Iterated Unit

Apply A three times
  • 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.
  • Examples: Grid & Comb Pattern

Conditional Unit

If A applicable then apply B, else apply C
  • 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.
  • Examples: Java2StateMachine

Multi-Units

A Multi-Unit has an arbitrary number of sub-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: 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.
  • Examples: Ecore2RDB, Java2StateMachine, Ecore2Genmodel, Grid & Comb Pattern, Movies

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.
  • Examples: Java2StateMachine

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.
  • Examples: Ecore2Genmodel

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