## How to create a model facet set

The first step is to [[MoDisco/ProjectNature|create a MoDisco project]].

The second step is to [[MoDisco/QueryManager|create a query set]]. This query set will store boolean queries indicating if an object conforms to a facet.

Right-click on the MoDisco project and select New > Other....

Select Facet Model and press the Next button

Choose a name for your model facet set (My.facetSet in the example) and press Finish.

Open the "My.facetSet" file and open the Properties View.

Set the name of the facet set and make sure that the facet set name is the same as the containing file name ("My" in the example). The nsURI and prefix must also be filled.

Load the resources containing the meta-model extended by the facet set. To load a meta-model resource you must use the Load Meta-model Resource action.

In this example, we choose to use the Java meta-model.

Fill the Extended Package field with the ePackage containing the virtually extended meta-model.

Right click on the FacetSet element and choose New Child > Facet to create a facet.

Set the facet name and the class that the facet will extend.

To specify how to know if an object conforms to a facet, we have to provide a boolean query. To provide this query we have to load the model containing its description.

Right-click in the editor and choose Load MoDisco Resource:

The query has to be referred to using the MoDisco protocol ("modisco:/query/<querySetName>"). In the example, we use the "My" query set.

Once the query set resource is referenced, we just have to select the query describing the facet. In the example this query is named "isAbstract".

At this step, if we save the model, the error marker should disappear from the file's icon, indicating that the facet set model is now valid.

If the facet has specific attributes or references which can be calculated, we can declare them. In this example, we will declare an attribute indicating the number of abstract methods contained in the abstract class. To create a new facet attribute right-click on the facet element and select the New Child > FacetAttribute.

The attribute's type and name must be set. The "Value Query" field must be filled with a reference to a query which is used to calculate the attribute's value. This query must have the same type as the attribute and be applicable to the virtually extended class.

The facet set is now ready to be used.

## How to consult the MoDisco facet set catalog through the UI

If a facet set model is valid, it is registered in the facet set catalog. To consult the facet set catalog, we can use the "Facet Set" view.

To open this view select Windows > Show view > Other ... in the menu bar and choose Facet Sets in the list.

The "Facet Sets" view presents the available facet sets and their facets. For each facet set the location of its description model is pointed out.

## How to programmatically use the MoDisco facet set catalog

Here is an example of using the MoDisco facet API. For more information please refer to the JavaDoc.

    import org.eclipse.emf.ecore.EObject;
    import org.eclipse.gmt.modisco.infra.query.core.exception.ModelQueryException;
    import org.eclipse.gmt.modisco.infra.facet.Facet;
    import org.eclipse.gmt.modisco.infra.facet.FacetSet;
    import org.eclipse.gmt.modisco.infra.facet.core.FacetSetCatalog;
    import org.eclipse.gmt.modisco.infra.facet.core.exception.ModiscoFacetException;

    public class Example {

    	public Integer getNbAbstractMethod(EObject eObject)
    			throws ModelQueryException, ModiscoFacetException {
    		FacetSet facetSet = FacetSetCatalog.getSingleton().getFacetSet("My");
    		FacetContext context = new FacetContext();
    		context.addFacetSet(facetSet);
    		Facet facet = facetSet.getFacet("AbstractClassDeclaration");
    		if (context.isInstance(eObject, facet)) {
    			Object object = context.get(eObject, facet
    					.getEStructuralFeature("nbAbstractMethod"));
    			if (object instanceof Integer) {
    				Integer nbAbstractMethod = (Integer) object;
    				return nbAbstractMethod;
    			}
    		}
    		return null;
    	}
    }

## How to package a facet set in a plug-in

To package a facet set in a plug-in, an extension must be added in the plugin.xml file (contained by the facet set's project). The extension point to use is: org.eclipse.gmt.modisco.infra.facet.registration. Here is an example of a facet set declaration:

     <plugin>
          <extension
              point="org.eclipse.gmt.modisco.infra.facet.registration">
           <facetset
                 file="_example_jdkAndEclipseFacets.facetSet">
           </facetset>
        </extension>
     </plugin>

Thanks to this extension declaration, the MoDisco project is ready to be exported as a plug-in.

## Facet Meta-model Description

The facet meta-model extends the ecore meta-model and uses the query meta-model.

A FacetSet is a kind of EPackage. A FacetSet contains facets through the eClassifier reference. A facet is a kind of EClass.

For a facet instance, the eSuperType reference must be set to specify which class the facet virtually extends.

The facet class has one specific reference: conditionQuery. The conditionQuery reference points to the ModelQuery class. The model queries pointed to by the conditionQuery reference must return a Boolean. Those queries are used to specify how to decide whether an instance conforms to a facet. If the conditionQuery is empty then all the instances of the class referred to by the facet instance through the eSuperType reference conform to this facet.

A facet contains facetAttributes and facetReferences through the eStructuralFeature reference. The FacetAttribute and FacetReference classes have a common super class: FacetStructuralFeature. The FacetStructuralFeature has one reference named valueQuery pointing to the ModelQuery class. The valueQuery is used to compute the facet structural feature value. The facetAttribute and facetReference must have the same type as the query they refer to.

Category:MoDisco

## Updating This Document

This document is maintained in a collaborative wiki. If you wish to update or modify this document please visit http://wiki.eclipse.org/MoDisco/Components/FacetManager/Documentation/0.8