Henshin/Textual Editor

The textual Henshin editor supports the specification of transformation rules and units with syntax highlighting, quick fixes and content assist.

Creating a new henshin_text file

To create a new henshin_text file you need to open New wizard and select Henshin Text from the category Henshin. The wizard will create a new henshin_text file and will add the XText nature to your project.

Specifying transformation rules and units

Specifying transformation rules

The below code shows the textual definition of the transformation rule createAccount (bank example). The definition of this rule starts with the keyword rule, followed by its unique name createAccount. The two parameters client and accountId are defined by specifying their kind, followed by their name and their type. The nodes and edges of the rule are then defined within a graph element.

ePackageImport bank
 
rule createAccount(IN client:EString,IN accountId:EInt){
	graph{
		node bank:Bank
		preserve node manager:Manager
		preserve node client:Client
 
		create node newAccount:Account{
			create id=accountId
		}
 
		forbid node account:Account{
			id=accountId
		}
 
		edges[(bank->manager:managers),(preserve bank->client:clients),(forbid bank->account:accounts)]
 
		edges[(manager->client:clients),(create client-> newAccount:accounts),(create bank-> newAccount:accounts)]
	}
}

The definition of a node starts with its action (preserve, create, delete, forbid, require), followed by the keyword node, a unique name for the node and its type. Nodes without an action, e.g. bank, have always the action preserve. If a node has attributes, these are written in curly brackets after its definition. For each attribute its action can be defined, as for the id of newAccount in the code example. Is no action defined an attribute has the same action as its node. E.g., the attribute id of account has the action forbid. Edges between nodes are defined as list after the keyword edges. Several lists of edges can be defined, as shown in the code example. An edge definition is always enclosed in brackets and consists of its action, the name of the source node, ->, the name of the target node and its type. If no action is specified, as it is for (bank->manager:managers), the action of the edge is preserve.

Specifying multi-rules

The below code shows the textual definition of the transformation rule scheduleOfferedCourse (university courses example). Within the element graph the multi-rule to associate students with the ScheduledCourse is defined after the keyword multiRule and its name moveStudentsToScheduledCourse. Inside a multiRule there is always a graph element in which the multi-rule can be defined the same way as a transformation rule. To use nodes from the kernel rule in a multi-rule, only their names must be used. For example, inside the multi-rule the edge (delete student->offered:isInterestedIn), defines that an edge from the node student (part of the multi-rule) to the node offered (part of the kernel rule) should be deleted.

rule scheduleOfferedCourse(IN hour:EInt, OUT offered:OfferedCourse, VAR name:EString){
	conditions [hour>=0, hour<24]
	graph{
		node root:University
 
		node offered:OfferedCourse{
			name=name
		}
 
		node lecturer:Lecturer
 
		edges[(root->offered:courses),(root->lecturer:persons),(delete lecturer->offered:canTeach)]
 
		create node scheduled:ScheduledCourse{
			name=name
			startingHour=hour
		}
 
		edges[(create lecturer->scheduled:teaches),(create root->scheduled:courses),(create scheduled->lecturer:lecturers)]
 
		forbid node notScheduled:ScheduledCourse{
			startingHour=hour
		}
		edges[(forbid root->notScheduled:courses),(forbid lecturer->notScheduled:teaches),(forbid notScheduled->lecturer:lecturers)]
 
		require node requiredStudent:Student
 
		edges[(require root->requiredStudent:persons),(require requiredStudent->offered:isInterestedIn)]
 
 
		multiRule moveStudentsToScheduledCourse {
			graph{
				node student:Student
				edges[(delete student->offered:isInterestedIn), (create student->scheduled:isInterestedIn), (root->student:persons)]
 
				forbid node forbidScheduledCourseMove:ScheduledCourse{
					startingHour=hour
				}
 
				edges[(forbid root->forbidScheduledCourseMove:courses),(forbid student->forbidScheduledCourseMove:isInterestedIn)]
 
			}
		}
 
	}
}

Specifying Application Conditions

There are two ways to specify application conditions with the textual syntax for Henshin. One way is to annotate nodes with the actions forbid and require. An example for such annotated nodes can be seen in the example code in section 2.1. Specifying Multi-rules. If the actions require and forbid are combined, as in the example, a positive application condition (PAC) and a negative application conditions (NAC) are created, which are combined using AND (more about PAC and NAC here). The other way is to define individual graphs to specify application conditions. This option also allows to express more complex application conditions. The below code shows the textual definition of the transformation rule scheduleOfferedCourse (university courses example). In this example the application condition is defined within the element matchingFormula. Inside a matchingFormula positive application conditions are defined as individual graphs. A graph definition starts with the keyword conditionGraph and a unique name, followed by the graph definition consisting of nodes and edges. Within these graphs, nodes from the left-hand side (LHS) can be used by using their names. E.g., within the application condition StudentIsInterested the edge (root->requiredStudent:persons) connects the node root from the LHS with the node requiredStudent from the PAC. To combine the graphs defining application conditions and to define NACs the keyword formula within the element matchingFormula is used. After the keyword formula, the application conditions can be combined with OR, AND, and XOR using their names. To define a NAC a ! must be written before the name. The below code example shows that the application condition teachAnotherScheduledCourseSameTime is a NAC, that is combined with the PAC StudentIsInterested by an AND.

rule scheduleOfferedCourseFormula(IN hour:EInt, OUT offered:OfferedCourse, VAR name:EString){
	conditions [hour>=0, hour<24]
	graph{
		node root:University
 
		node offered:OfferedCourse{
			name=name
		}
 
		node lecturer:Lecturer
 
		edges[(root->offered:courses),(root->lecturer:persons),(delete lecturer->offered:canTeach)]
 
		create node scheduled:ScheduledCourse{
			name=name
			startingHour=hour
		}
 
		edges[(create lecturer->scheduled:teaches),(create root->scheduled:courses),(create scheduled->lecturer:lecturers)]
 
		matchingFormula {
			formula !teachAnotherScheduledCourseSameTime AND StudentIsInterested
 
			conditionGraph teachAnotherScheduledCourseSameTime{
				node notScheduled:ScheduledCourse{
					startingHour=hour
				}
				edges[(root->notScheduled:courses),(lecturer->notScheduled:teaches),(notScheduled->lecturer:lecturers)]
			}
 
			conditionGraph StudentIsInterested{
				node requiredStudent:Student
 
				edges[(root->requiredStudent:persons),(requiredStudent->offered:isInterestedIn)]
			}
 
		}
 
 
		multiRule moveStudentsToScheduledCourse {
			graph{
				node student:Student
				edges[(delete student->offered:isInterestedIn), (create student->scheduled:isInterestedIn), (root->student:persons)]
 
				forbid node forbidScheduledCourseMove:ScheduledCourse{
					startingHour=hour
				}
 
				edges[(forbid root->forbidScheduledCourseMove:courses),(forbid student->forbidScheduledCourseMove:isInterestedIn)]
 
			}
		}
 
	}
}

Specifying Units

The following code examples show how to define the different units. The Independent Unit is taken from the (example Ecore2GenModel) and the other units are taken from the (example University Courses).

Independent Unit

unit generateGenModel(IN modelFileName:EString, IN pluginName:EString, OUT genModel:GenModel){
	independent [createGenModel(modelFileName, pluginName, genModel), createGenPackage(), createGenClass(), createGenFeatureForAttribute(), createGenFeatureForReference()]
}

Priority Unit

unit planOrCleanup(IN startHour:EInt){
	priority [ planAllCoursesOrFail(startHour), cleanupUninterestingCourses()]
}

Sequential Unit

unit planAllCoursesOrFail(IN startHour:EInt){
	existsUnscheduledInterestingCourse()
	planCourseOrIncrement(startHour)
}

Loop Unit

 
unit cleanUpUniterestingCoursesUnit(){
	while{
		cleanupUninterestingCourses()
	}
}

Iterated Unit

unit manageCourses(IN startHour:EInt){
	for(2){
		planOrCleanup(startHour)
	}
}

Conditional Unit

The first example code shows a Conditional Unit with else-part the second example is a Conditional Unit without else-part.

unit planCourseOrIncrement(IN currentHour:EInt){
	if (planOneCorse(currentHour)) then {
		planUnscheduledInterestingCourses(currentHour)
	}else {
		incrementIfPossible(currentHour)
	} 
}

unit planUnscheduledInterestingCourses(IN currentHour:EInt){
	if(existsUnscheduledInerestingCourse())then {
		planCourseOrIncrement(currentHour)
	}
}

In the textual syntax it is also possible to nest different unit definitions. E.g., the below code shows the definition of the Conditional Unit planUnscheduledInterestingCourses, which calls in its then-part the Conditional Unit planCourseOrIncrement. But in this example, the definition of planCourseOrIncrement is nested.

unit planUnscheduledInterestingCourses(IN currentHour:EInt){
	if(existsUnscheduledInerestingCourse())then {
		//Start: nested definition of planCourseOrIncrement
		if (planOneCorse(currentHour)) then {
			planUnscheduledInterestingCourses(currentHour)
		}else {
			incrementIfPossible(currentHour)
		}
		//End: nested definition of planCourseOrIncrement
	}
}

Running a transformation rule or unit

To run a transformation rule or unit you need to right-click on your henhin_text file and select „Apply transformation“. This will invoke the interpreter wizard. It is also possible to generate a henshin file. For this you need to right-click on your henhin_text file and select „Transform to Henshin“.