EMF Compare FAQ

Users

My model is compared as a text-file, how can EMF compare know what file it should handle ?

Q : My model is compared as a text-file, how can EMF compare know what file it should handle ?

A : EMF compare uses a content-type to know if it should be started or not. By default this content-type is composed of *.ecore and *.uml file but you may add your own extension using the Preferences view / Global / Content-types and adding your file extension in the "Model File" content-type.

Developpers

How can I programatically add my model file extension in EMF Compare so that it is called automatically ?

Q : How can I programatically add my model file extension in EMF Compare so that it is called automatically ?

A : Using the "Model File" content-type defined with EMF Compare, here is a sample from a plugin.xml:

 <extension
        point="org.eclipse.core.contenttype.contentTypes">
     <file-association
           content-type="org.eclipse.emf.compare.ui.contenttype.ModelContentType"
           file-extensions="uml13"
           file-names="*"/>
  </extension>

Is EMF Compare, as EMF, able to run outside of Eclipse ?

Q : Is EMF Compare able to compare "in-memory" objects, and can it be run without Eclispe ?

A: Yes, here is a snippet doing that:

 /**
 * This application will try and launch an headless model comparison.
 * 
 * @author Cedric Brun <a href="mailto:cedric.brun@obeo.fr">cedric.brun@obeo.fr</a>
 */
public final class ExampleLauncher {
	/**
	 * This class doesn't need to be instantiated.
	 */
	private ExampleLauncher() {
		// prevents instantiation
	}

	/**
	 * Launcher of this application.
	 * 
	 * @param args
	 *            Arguments of the launch.
	 */
	public static void main(String[] args) {
		if (args.length == 2 && new File(args[0]).canRead() && new File(args[1]).canRead()) {
			// Creates the resourceSet where we'll load the models
			final ResourceSet resourceSet = new ResourceSetImpl();
			try {
				// Loads the two models passed as arguments
				final EObject model1 = ModelUtils.load(new File(args[0]), resourceSet);
				final EObject model2 = ModelUtils.load(new File(args[1]), resourceSet);
				
				// Creates the match then the diff model for those two models
				final MatchModel match = new DifferencesServices().modelMatch(model1, model2, new NullProgressMonitor());
				final DiffModel diff = new DiffMaker().doDiff(match);
				
				// Prints the results
				try {
					System.out.println(ModelUtils.serialize(match));
					System.out.println(ModelUtils.serialize(diff));
				} catch (IOException e) {
					e.printStackTrace();
				}
				
//				System.out.println("saving diff as \"result.diff\"");
//				ModelUtils.save(diff, "result.diff");
//				System.out.println("saving match as \"result.match\"");
//				ModelUtils.save(match, "result.match");
				
				// Serializes the result as "result.emfdiff" in the directory this class has been called from.
				System.out.println("saving emfdiff as \"result.emfdiff\""); //$NON-NLS-1$
				final ModelInputSnapshot snapshot = DiffFactory.eINSTANCE.createModelInputSnapshot();
				snapshot.setDate(Calendar.getInstance().getTime());
				snapshot.setMatch(match);
				snapshot.setDiff(diff);
				ModelUtils.save(snapshot, "result.emfdiff"); //$NON-NLS-1$
			} catch (IOException e) {
				// shouldn't be thrown
				e.printStackTrace();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		} else {
			System.out.println("usage : Launcher <Model1> <Model2>"); //$NON-NLS-1$
		}
	}
}

What kind of "strategies" use EMF compare ?

Q : What kind of "strategies" use EMF compare ? On which research work is it based ?

A : The emf compare generic engine is based on several research work and on experimentations. The paper being the most "near" the emf compare behavior is probably "UMLDiff: An Algorithm for Object-OrientedDesign Differencing" by Zhenchang Xing and Eleni Stroulia. Other reseach work have been used and a lot of them use the same kind of general behavior: A comparison in 2 phases, the first being the matching phase and the second the differencing phase. The matching is done computing comparison metrics and getting an "overall" rank of matching for two nodes while browsing both versions of the model. These metrics may change considering the research work, here in the generic engine we use 4 metrics :

• type similarity : analysing the metamodel element
• name similarity : looking for an attribute which have chances to be the

name and comparing it

• value similarity : analysing the whole attributes values
• relations similarity : using the relations the element has with others.

Using these 4 metrics the comparison engine provide good correctness (most especially comparing models from DSM/DSL's metamodels) and efficiency when comparing big models (~=100 000 elements).

Once the matching phase is done, the matching model is browsed by the differencing engine computing "added", "deleted" or updated elements from that. If you save a comparison as an emfdiff model you'll be able to browse the match and diff model and you'll get the similarity ranking for each couple of elements.

We're open to suggestion to enhance this generic behavior but we are also open to other methods : we want this component to be a testbed for other algorithms and comparison techniques, any Eclipse plugin may contribute its own matching and differencing engine for generic or specific purpose and it would be quite interesting to compare the results from different engines on different models.

What evolution should we expect on the global EMF compare strategies ?

Q : What evolution should we expect on the global EMF compare strategies ?

A : We are trying to get better results with generic comparison algorithm through other methods coming from the research world. An initiative about model transformation/weaving and comparison is taking place in Europe an you may expect that the EMF compare implementation will evolve toward these works.

Model Transformation initiative