String extendingFieldClass = "java.lang.String";
String extendingFieldLabelValue = "Attribute B2.1";
String extendingFieldDescriptionValue = "First attribute of B2";
int extendingFieldPositionValue = 1;
ObjectPropertyTO extendingProp = new ObjectPropertyTO(extendingFieldName, extendingFieldClass, false, true);
extendingProp.addAnnotation(annotationDefs.get(AnnotationDefinitionTO.LABEL_ANNOTATION), AnnotationDefinitionTO.VALUE_PARAM, extendingFieldLabelValue);
extendingProp.addAnnotation(annotationDefs.get(AnnotationDefinitionTO.DESCRIPTION_ANNOTATION), AnnotationDefinitionTO.VALUE_PARAM, extendingFieldDescriptionValue);
extendingProp.addAnnotation(annotationDefs.get(AnnotationDefinitionTO.POSITION_ANNOTATION), AnnotationDefinitionTO.VALUE_PARAM, extendingFieldPositionValue);
extending.setProperties(Arrays.asList(extendingProp));
GenerationResult result = modelerService.saveModel(dataModel, project);