diff --git a/.github/workflows/maven.yml b/.github/workflows/maven.yml
index 8b52c48..8aa754a 100644
--- a/.github/workflows/maven.yml
+++ b/.github/workflows/maven.yml
@@ -13,7 +13,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Set up JDK 11
-      uses: actions/setup-java@v2
+      uses: actions/setup-java@v3
       with:
         distribution: 'temurin'
         java-version: '11'
diff --git a/repository/src/main/resources/xsd/repository.xsd b/repository/src/main/resources/xsd/repository.xsd
index f5c0c02..6cfc286 100644
--- a/repository/src/main/resources/xsd/repository.xsd
+++ b/repository/src/main/resources/xsd/repository.xsd
@@ -198,13 +198,13 @@
 				<xs:element name="metadata" type="dcterms:elementOrRefinementContainer"/>
 				<xs:element ref="fixr:categories" minOccurs="0"/>
 				<xs:element ref="fixr:sections" minOccurs="0"/>
-				<xs:element ref="fixr:datatypes"/>
+				<xs:element ref="fixr:datatypes" minOccurs="0"/>
 				<xs:element ref="fixr:codeSets" minOccurs="0"/>
-				<xs:element ref="fixr:fields"/>
+				<xs:element ref="fixr:fields" minOccurs="0"/>
 				<xs:element ref="fixr:actors" minOccurs="0"/>
 				<xs:element ref="fixr:components" minOccurs="0"/>
 				<xs:element ref="fixr:groups" minOccurs="0"/>
-				<xs:element ref="fixr:messages"/>
+				<xs:element ref="fixr:messages" minOccurs="0"/>
 				<xs:element ref="fixr:concepts" minOccurs="0"/>
 				<xs:element ref="fixr:scenarios" minOccurs="0"/>
 				<xs:element name="annotation" type="fixr:annotation" minOccurs="0"/>