Henshin/Units

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.

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 and 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

Apply A then B then C

• 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 and Comb Pattern, Movies

Priority Unit

Try to apply A. If A not applicable, try B etc.

• 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

Choose A, B or C in non-deterministic order. If not applicable, try another one in non-deterministic order. If it is not applicable...

• 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