1 files changed, 15 insertions, 10 deletions

diff --git a/subprojects/language/src/main/java/tools/refinery/language/utils/ProblemUtil.java b/subprojects/language/src/main/java/tools/refinery/language/utils/ProblemUtil.java
index f70893e0..9daa8f61 100644
--- a/subprojects/language/src/main/java/tools/refinery/language/utils/ProblemUtil.java
+++ b/subprojects/language/src/main/java/tools/refinery/language/utils/ProblemUtil.java
@@ -1,5 +1,5 @@
 /*
- * SPDX-FileCopyrightText: 2021-2023 The Refinery Authors <https://refinery.tools/>
+ * SPDX-FileCopyrightText: 2021-2024 The Refinery Authors <https://refinery.tools/>
  *
  * SPDX-License-Identifier: EPL-2.0
  */
@@ -81,6 +81,9 @@ public final class ProblemUtil {
         }
 
         public static boolean hasMultiplicityConstraint(ReferenceDeclaration referenceDeclaration) {
+                if (referenceDeclaration.getReferenceType() instanceof DatatypeDeclaration) {
+                        return false;
+                }
                 var opposite = referenceDeclaration.getOpposite();
                 if (opposite != null && opposite.getKind() == ReferenceKind.CONTAINMENT) {
                         return false;
@@ -95,17 +98,19 @@ public final class ProblemUtil {
                 return true;
         }
 
-        public static int getArity(Relation relation) {
-                if (relation instanceof ClassDeclaration || relation instanceof EnumDeclaration) {
-                        return 1;
-                }
-                if (relation instanceof ReferenceDeclaration) {
-                        return 2;
+        public static boolean isTypeLike(Relation relation) {
+                if (relation instanceof ClassDeclaration || relation instanceof EnumDeclaration ||
+                                relation instanceof DatatypeDeclaration) {
+                        return true;
                 }
                 if (relation instanceof PredicateDefinition predicateDefinition) {
-                        return predicateDefinition.getParameters().size();
+                        return predicateDefinition.getParameters().size() == 1;
                 }
-                throw new IllegalArgumentException("Unknown Relation: " + relation);
+                return false;
+        }
+
+        public static boolean isContainmentReference(ReferenceDeclaration referenceDeclaration) {
+                return referenceDeclaration.getKind() == ReferenceKind.CONTAINMENT;
         }
 
         public static boolean isContainerReference(ReferenceDeclaration referenceDeclaration) {
@@ -116,7 +121,7 @@ public final class ProblemUtil {
                 return switch (kind) {
                         case CONTAINMENT -> false;
                         case CONTAINER -> true;
-                        case REFERENCE -> {
+                        case DEFAULT, REFERENCE -> {
                                 var opposite = referenceDeclaration.getOpposite();
                                 if (opposite == null) {
                                         yield false;