Difference between revisions of "EMF/Generating Dynamic Ecore from XML Schema"

Latest revision as of 05:24, 13 December 2010

EMF and XML - An Introduction
In this Wiki document, I have tried to document the steps involved in generating Ecore using XML Schema, loading an XML file into an Ecore model, and so on.

1. Convert a given XSD into Ecore
2. Load an XML according to the generated Ecore
3. Display the loaded model using a TreeViewer

For this code to execute, you need to include the following plugins as dependencies

• org.eclipse.emf.ecore
• org.eclipse.xsd
• org.eclipse.emf.ecore.xmi
• org.eclipse.emf.edit.ui

Convert a XSD into Ecore

The following code snippet would enable you to load an existing XSD and convert it into an Ecore.

    XSDEcoreBuilder xsdEcoreBuilder = new XSDEcoreBuilder();
    ResourceSet resourceSet = new ResourceSetImpl();
    Collection eCorePackages = xsdEcoreBuilder.generate(URI.createFileURI("D:/model/example.xsd"));

Note: Running this code could get you a NullPointerException or schema FileNotFoundException with running on a 1.4 Sun JVM. This is due to the ever popular Crimsom DOM bug. Please refer to the following link to find a workaround to this problem.Manifestation of Crimsom DOM Bug

For these loaded Ecores to be available, we need to register them to the package registry.

    for (Iterator iter = eCorePackages.iterator(); iter.hasNext();) {
	EPackage element = (EPackage) iter.next();
	resourceSet.getPackageRegistry().put(element.getNsURI(), element);	
    }

Load an XML into the Ecore

    HashMap options = new HashMap();
    options.put(XMLResource.OPTION_EXTENDED_META_DATA, Boolean.TRUE);
    Resource resource = resourceSet.createResource(URI.createFileURI("D:/model/example.xml"));
    resource.load(options);

Note: The XML file should contain an xsi:schemaLocation. EMF provides this a built-in feature wherein if the XML knows its schema, EMF would build the model from the schema and load the XML without having to perform Step 1.Convert XSD into Ecore.

If no schemaLocation is specified, at least the namespace should be specified so that it may search for the package in the package registry registered with the same namespace and load the XML according to that Ecore model.

If neither a schemaLocation nor namespace are not provided, XML would be loaded with a default schema provided by EMF which would consider all the nodes as xsd:anyType.

Since some of the XML Schema specific contructs are not represented directly in Ecore, they are represented as Ecore Annotations. These annotations are termed as ExtendedMetaData and to query them we need to use the ExtendedMetaData APIs. Therefore to load an XML which contains the schemaLocation we need to provide the loading option XMLResource.OPTION_EXTENDED_META_DATA as true as shown in the code above.

Display using a TreeViewer

    List factories = new ArrayList();
    factories.add(new ResourceItemProviderAdapterFactory());
    factories.add(new ReflectiveItemProviderAdapterFactory());
    
    ComposedAdapterFactory adapterFactory = new ComposedAdapterFactory(factories);

    TreeViewer tViewer = new TreeViewer(parent);
    tViewer.setContentProvider(new AdapterFactoryContentProvider(adapterFactory));
    tViewer.setLabelProvider(new AdapterFactoryLabelProvider(adapterFactory));
    tViewer.setInput(resourceSet);

Further Reading
Discover the Eclipse Modeling Framework (EMF) and Its Dynamic Capabilities
Newsgroup Msg11109
Binding XML to Java
--Annamalai.chockalingam.gmail.com 18:06, 10 February 2007 (EST)