diff --git a/plugins/org.eclipse.ocl.pivot/src/org/eclipse/ocl/pivot/options/PivotValidationOptions.java b/plugins/org.eclipse.ocl.pivot/src/org/eclipse/ocl/pivot/options/PivotValidationOptions.java
index 2ad92a2..2814b68 100644
--- a/plugins/org.eclipse.ocl.pivot/src/org/eclipse/ocl/pivot/options/PivotValidationOptions.java
+++ b/plugins/org.eclipse.ocl.pivot/src/org/eclipse/ocl/pivot/options/PivotValidationOptions.java
@@ -38,10 +38,12 @@
 			PivotPlugin.PLUGIN_ID, "missing.safe.navigation", StatusCodes.Severity.IGNORE, StatusCodes.Severity.class); //$NON-NLS-1$
 
 	/**
+	 * Specify the interpretation of default multiplicities; true for Ecore-like optional [?]. false for UML-like required [1].
+	 *
 	 * @since 1.16
 	 */
 	public static final @NonNull BooleanOption OptionalDefaultMultiplicity = new BooleanOption(
-		PivotPlugin.PLUGIN_ID, "optional.default.multiplicity", true); //$NON-NLS-1$
+		PivotPlugin.PLUGIN_ID, "optional.default.multiplicity", false); //$NON-NLS-1$
 
 	public static final @NonNull EnumeratedOption<StatusCodes.Severity> RedundantSafeNavigation = new EnumeratedOption<StatusCodes.Severity>(
 			PivotPlugin.PLUGIN_ID, "redundant.safe.navigation", StatusCodes.Severity.IGNORE, StatusCodes.Severity.class); //$NON-NLS-1$
diff --git a/plugins/org.eclipse.ocl.xtext.base/src/org/eclipse/ocl/xtext/base/cs2as/CS2ASConversion.java b/plugins/org.eclipse.ocl.xtext.base/src/org/eclipse/ocl/xtext/base/cs2as/CS2ASConversion.java
index ae19355..615de1d 100644
--- a/plugins/org.eclipse.ocl.xtext.base/src/org/eclipse/ocl/xtext/base/cs2as/CS2ASConversion.java
+++ b/plugins/org.eclipse.ocl.xtext.base/src/org/eclipse/ocl/xtext/base/cs2as/CS2ASConversion.java
@@ -1114,7 +1114,11 @@
 	public void refreshRequiredType(@NonNull TypedElement pivotElement, @NonNull TypedRefCS csTypeRef) {
 		org.eclipse.ocl.pivot.Class type = PivotUtil.getPivot(org.eclipse.ocl.pivot.Class.class, csTypeRef);
 		Boolean isRequired = converter.isRequired(csTypeRef);
-		getHelper().setType(pivotElement, type, isRequired != Boolean.FALSE);
+		if (isRequired == null) {
+			boolean defaultIsOptional = getEnvironmentFactory().getValue(PivotValidationOptions.OptionalDefaultMultiplicity) == Boolean.TRUE;
+			isRequired = !defaultIsOptional;
+		}
+		getHelper().setType(pivotElement, type, isRequired.booleanValue());
 	}
 
 	public void refreshTemplateSignature(@NonNull TemplateableElementCS csTemplateableElement, @NonNull TemplateableElement pivotTemplateableElement) {