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ATL/Howtos

< ATL
Revision as of 16:03, 18 December 2006 by Frederic.jouault.univ-nantes.fr (Talk | contribs) (added how to handle arbitrary XML documents)

< To: ATL

This page contains a list of problems related to ATL usage. It gives hints towards solutions and links to examples.

How do I generate text from models?

There are several possibilies. We only detail some of them here.

Using ATL

You can specify a query over your model in ATL. An example of this is available in the UML2Java transformation.

The atlanticRaster zoo is also using this technique. It first transforms KM3 metamodels into DOT models with the KM32DOT.atl transformation. It then uses DOT2Text.atl to query a String from the DOT model. This string corresponds to the generated DOT code. Then, the build.xml ant scripts makes use of the am3.saveModel task with an ATL extractor pointing to the DOT2Text.atl transformation.

Using TCS

TCS (Textual Concrete Syntax) is a tool enabling the specification of textual syntaxes for metamodels. Once such a syntax has been specified, models can be serialized to text files.

One advantage of TCS is that text can also be parsed into models. It is therefore possible to use the same specification to enable the definition of models with any text editor.

How do I launch transformations programmatically?

The ATL development environment (ATL Development Tools, or ADT) provides several means to launch transformations:

  • by specifying a launch configuration,
  • by writing an ant script using the AM3 Ant Tasks.

However, in some cases, it is necessary to launch an ATL transformation from Java code. The AtlLauncher class can be used for this purpose. The KM3Projector class of the KM3 plugin contains example usages of the AtlLauncher class (e.g. the getEcoreFromKM3 method).

Remark 1: the AtlCompiler class may be used to compile ATL transformations into .asm files executable on the ATL Virtual Machine.

Remark 2: There may be problem when using MDR as model handler, as it shown in KM3Projector class. Call to initMDR() method should be done only once when your class is constructed. This is because if you load your model in this way: getMDRModelHandler().loadModel("model.xmi", getSomeMetamodel(), mod.openStream()); method getSomeMetamodel() will return reference to metamodel which is initialized in initMDR(). If some of your methods later call initMDR() your initial metamodel reference will be lost and someMetamodel variable will get reference to new metamodel. Result of your transformation will be output model file, because input model has lost his metamodel reference.

How do I use extern parameters in ATL transformations?

Using an XML file

A solution is to save transformation parameters in a extern XML model. In the transformation, you will use an helper to get parameters from your model. The wanted parameters model will be chosen in the transformation launch configuration or in the AM3 Ant Tasks.

The following code is a simple parameters XML file:

<parameters>
	<param name="source" value="KM3"/>
	<param name="target" value="ATL"/>
</parameters>

In the transformation header, you add the parameters model and its metamodel XML.km3 :

module AMW2ATL;
create OUT : ATL from source : MOF, target : MOF, parameters : XML;

From parameters model, the following helper is used to get value attribute select in the param entities according to the given name:

helper def : getParameter(name : String) : String =
	XML!Element.allInstancesFrom('parameters')->select(e |
		e.name = 'param'
	)->select(e |
		e.getAttrVal('name') = name
	)->first().getAttrVal('value');

To used the previous helper (due to the getAttrVal call), you need to used XMLHelpers.asm ATL Library and add in the transformation:

uses XMLHelpers;

The following code, it is a simple example to show how to used getParameter helper:

helper def : sourceValue  : String = thisModule.getParameter('source');

In AM3 Ant Tasks, you need to add the parameters model, the XML.km3 metamodel and the XMLHelpers.asm library. For this you need parameters.xml model in ecore. See the following example:

<am3.loadModel modelHandler="EMF" name="KM3" metamodel="MOF" path="uri:http://www.eclipse.org/gmt/2005/KM3"/>

<am3.loadModel modelHandler="EMF" name="XML" metamodel="KM3" path="XML.km3">
	<injector name="ebnf">
		<param name="name" value="KM3" />
	</injector>
</am3.loadModel>

<am3.loadModel modelHandler="EMF" name="Parameters" metamodel="XML" path="Parameters.xml">
	<injector name="xml"/>
</am3.loadModel>

<am3.atl path="myTransformation.atl">
	<inModel name="source" model="left"/>
	<inModel name="target" model="right"/>
	<inModel name="MOF" model="%EMF"/>

	<inModel name="parameters" model="Parameters"/>
	<inModel name="XML" model="XML"/>
	<library name="XMLHelpers" path="XMLHelpers.asm"/>

	<inModel name="ATL" model="ATL"/>
	<outModel name="OUT" model="ATLmodel" metamodel="ATL"/>
</am3.atl>

<am3.saveModel model="ATLmodel" path="ATLmodel.ecore"/>	

Instead of AM3 Ant Tasks, if you use ATL launch configuration then you need to inject XML.km3 metamodel and parameters.xml into ecore model. Moreover, you need to add XMLHelpers.asm ATL library.

How can I specify a Virtual Machine operation in Java?

It is possible to add new Java operations to the ATL Virtual Machine (VM). These operations can then be called like helpers.

The org.eclipse.gmt.atl.oclquery.core plugin offers the org.eclipse.gmt.atl.oclquery.core.ATLVMTools class to create instances of org.atl.engine.vm.Operation and to register them in the ATL VM.

This is used in org.eclipse.gmt.atl.oclquery.core.OclEvaluator to redefine the dumpASM method of ASMEmitter. The process to register operations on OCL primitive types (e.g. Boolean, Integer, String) is similar.

How can I tune the XML output of ATL?

The ATL Virtual Machine can write target models to XML files in two different ways:

  • XMI writing is delegated to the model handler used to handle the model (e.g., EMF, MDR).

It is usually not possible to change the target format in this case because XMI support in each model handler implements a precise mapping from a metamodel to an XML Schema. However, different model handlers may produce different XMI files (e.g., XMI 2.0 with EMF, XMI 1.2 with MDR).

  • Target models can be extracted into XML files using custom XML Schemas.

To do this, the target model is first transformed into a model conforming to a specific XML metamodel. The resulting XML model can then be extracted into an XML document. An example can be found in the Table2SVGPieChart transformation scenario: the target SVG model is transformed into an XML model that can then be extracted (see documentation of scenario for more details and README.txt in zip file for directions). The process of transforming a model to XML then extracting it can be automated using ant tasks. This is also illustrated by the Table2SVGPieChart scenario (see build.xml in the zip file).

Remarks:

  • You always obtain XMI files (and thus non-customizable XML output) after running a launch configuration.

To obtain a custom XML file, you need to use the XML extractor (see build.xml in the zip file of Table2SVGPieChart for directions).

How can I handle arbitrary XML documents?

Arbitrary XML documents can be used as source or target of ATL transformations. However, this cannot be done directly (see previous section) but rather through injectors and extractors.

The XML injector can be executed from the contextual menu on files with the .xml extension, or from the am3.loadModel ant task. An example of using the XML injector is given in the how to use external parameter section.

The XML extractor can be executed from the contextual menu on files with the .ecore extension, or from the am3.saveModel ant task.

The XML injector is implemented in XMLInjector, which extends Injector.

The XML extractor is implemented in XMLExtractor, which extends Extractor.

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