diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index cae7a916..67e3c0a0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -165,7 +165,7 @@ jobs:
     needs: tests
     runs-on: ubuntu-latest
     env:
-      ONTOLOGY_GIT_TAG: v3.8.4
+      ONTOLOGY_GIT_TAG: v3.9.0
       ELASTIC_HOST: http://localhost:9200
       ELASTIC_FILEPATH: https://github.com/medizininformatik-initiative/fhir-ontology-generator/releases/download/TAGPLACEHOLDER/
       ELASTIC_FILENAME: elastic.zip
diff --git a/docker-compose.yml b/docker-compose.yml
index 59c273d0..debf362a 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -139,7 +139,7 @@ services:
     environment:
       ES_HOST: http://dataportal-elastic
       ES_PORT: 9200
-      ONTO_GIT_TAG: v3.8.4
+      ONTO_GIT_TAG: v3.9.0
       ONTO_REPO: https://github.com/medizininformatik-initiative/fhir-ontology-generator/releases/download
       DOWNLOAD_FILENAME: elastic.zip
       EXIT_ON_EXISTING_INDICES: false
diff --git a/pom.xml b/pom.xml
index ea2d9f2c..7ff334a0 100644
--- a/pom.xml
+++ b/pom.xml
@@ -27,7 +27,7 @@
     <java.version>17</java.version>
     <mockwebserver.version>5.1.0</mockwebserver.version>
     <okhttp3.version>4.10.0</okhttp3.version>
-    <ontology-tag>v3.8.4</ontology-tag>
+    <ontology-tag>v3.9.0</ontology-tag>
   </properties>
 
   <dependencies>
diff --git a/src/main/java/de/numcodex/feasibility_gui_backend/terminology/api/AttributeDefinition.java b/src/main/java/de/numcodex/feasibility_gui_backend/terminology/api/AttributeDefinition.java
index 1ab0b8ac..76137531 100644
--- a/src/main/java/de/numcodex/feasibility_gui_backend/terminology/api/AttributeDefinition.java
+++ b/src/main/java/de/numcodex/feasibility_gui_backend/terminology/api/AttributeDefinition.java
@@ -22,11 +22,13 @@ public record AttributeDefinition(
     @JsonProperty(value = "precision", required = true, defaultValue = "0") double precision,
     @JsonProperty(value = "min") Double min,
     @JsonProperty(value = "max") Double max,
-    @JsonProperty("referencedCriteriaSet") String referencedCriteriaSet,
-    @JsonProperty("referencedValueSet") String referencedValueSet
+    @JsonProperty("referencedCriteriaSet") List<String> referencedCriteriaSets,
+    @JsonProperty("referencedValueSet") List<String> referencedValueSets
 ) {
     public AttributeDefinition {
         selectableConcepts = (selectableConcepts == null) ? List.of() : selectableConcepts;
         allowedUnits = (allowedUnits == null) ? List.of() : allowedUnits;
+        referencedCriteriaSets = (referencedCriteriaSets == null) ? List.of() : referencedCriteriaSets;
+        referencedValueSets = (referencedValueSets == null) ? List.of() : referencedValueSets;
     }
 }
\ No newline at end of file
diff --git a/src/main/resources/static/v3/api-docs/swagger.yaml b/src/main/resources/static/v3/api-docs/swagger.yaml
index cac1e89f..a1a6d2bc 100644
--- a/src/main/resources/static/v3/api-docs/swagger.yaml
+++ b/src/main/resources/static/v3/api-docs/swagger.yaml
@@ -1442,13 +1442,17 @@ components:
           examples:
             - 1
         referencedCriteriaSet:
-          type: string
-          examples:
-            - http://fdpg.mii.cds/CriteriaSet/Diagnose/icd-10-gm
+          type: array
+          items:
+            type: string
+            examples:
+              - http://fdpg.mii.cds/CriteriaSet/Diagnose/icd-10-gm
         referencedValueSet:
-          type: string
-          examples:
-            - http://hl7.org/fhir/sid/icd-o-3
+          type: array
+          items:
+            type: string
+            examples:
+              - http://hl7.org/fhir/sid/icd-o-3
         type:
           type: string
           examples:
diff --git a/src/test/java/de/numcodex/feasibility_gui_backend/terminology/api/AttributeDefinitionTest.java b/src/test/java/de/numcodex/feasibility_gui_backend/terminology/api/AttributeDefinitionTest.java
index 6e751cba..f85e0529 100644
--- a/src/test/java/de/numcodex/feasibility_gui_backend/terminology/api/AttributeDefinitionTest.java
+++ b/src/test/java/de/numcodex/feasibility_gui_backend/terminology/api/AttributeDefinitionTest.java
@@ -23,8 +23,8 @@ void testConstructorWithValues() {
         .precision(0.0)
         .min(0.0)
         .max(0.0)
-        .referencedCriteriaSet(null)
-        .referencedValueSet(null)
+        .referencedCriteriaSets(null)
+        .referencedValueSets(null)
         .build();
 
     assertNotNull(attributeDefinition);
@@ -47,8 +47,8 @@ public void testConstructorWithNull() {
         .precision(0.0)
         .min(0.0)
         .max(0.0)
-        .referencedCriteriaSet(null)
-        .referencedValueSet(null)
+        .referencedCriteriaSets(null)
+        .referencedValueSets(null)
       .build();
 
     assertNotNull(attributeDefinition);
diff --git a/src/test/java/de/numcodex/feasibility_gui_backend/terminology/v5/TerminologyRestControllerIT.java b/src/test/java/de/numcodex/feasibility_gui_backend/terminology/v5/TerminologyRestControllerIT.java
index e550dff2..e82c7243 100644
--- a/src/test/java/de/numcodex/feasibility_gui_backend/terminology/v5/TerminologyRestControllerIT.java
+++ b/src/test/java/de/numcodex/feasibility_gui_backend/terminology/v5/TerminologyRestControllerIT.java
@@ -237,8 +237,8 @@ private AttributeDefinition createAttributeDefinition() {
             .attributeCode(createTermCode())
             .type(ValueDefinitonType.CONCEPT)
             .optional(false)
-            .referencedCriteriaSet("http://my.reference.criteria/set")
-            .referencedValueSet("http://my.reference.value/set")
+            .referencedCriteriaSets(List.of("http://my.reference.criteria/set"))
+            .referencedValueSets(List.of("http://my.reference.value/set"))
             .comparator(Comparator.EQUAL)
             .precision(1.0)
             .selectableConcepts(List.of(createTermCode()))