diff --git a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/ActionStatus.java b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/ActionStatus.java
index d38bc4f75..2b5daed2e 100644
--- a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/ActionStatus.java
+++ b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/ActionStatus.java
@@ -50,7 +50,7 @@ public interface ActionStatus extends TenantAwareBaseEntity {
     short getDownloadProgressPercent();
 
     /**
-     * @return list of message entries that can be added to the
+     * @return immutable list of message entries that in the
      *         {@link ActionStatus}.
      */
     List<String> getMessages();
diff --git a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/DistributionSetTag.java b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/DistributionSetTag.java
index 05089d138..9507e29b2 100644
--- a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/DistributionSetTag.java
+++ b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/DistributionSetTag.java
@@ -17,8 +17,8 @@ import java.util.List;
 public interface DistributionSetTag extends Tag {
 
     /**
-     * @return {@link List} of {@link DistributionSet}s this {@link Tag} is
-     *         assigned to.
+     * @return immutable {@link List} of {@link DistributionSet}s this
+     *         {@link Tag} is assigned to.
      */
     List<DistributionSet> getAssignedToDistributionSet();
 
diff --git a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/DistributionSetType.java b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/DistributionSetType.java
index cf5da40b2..57420bbad 100644
--- a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/DistributionSetType.java
+++ b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/DistributionSetType.java
@@ -27,15 +27,15 @@ public interface DistributionSetType extends NamedEntity {
     boolean isDeleted();
 
     /**
-     * @return set of {@link SoftwareModuleType}s that need to be in a
+     * @return immutable set of {@link SoftwareModuleType}s that need to be in a
      *         {@link DistributionSet} of this type to be
      *         {@link DistributionSet#isComplete()}.
      */
     Set<SoftwareModuleType> getMandatoryModuleTypes();
 
     /**
-     * @return set of optional {@link SoftwareModuleType}s that can be in a
-     *         {@link DistributionSet} of this type.
+     * @return immutable set of optional {@link SoftwareModuleType}s that can be
+     *         in a {@link DistributionSet} of this type.
      */
     Set<SoftwareModuleType> getOptionalModuleTypes();
 
diff --git a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/Rollout.java b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/Rollout.java
index 37185a8e2..72d7e7c53 100644
--- a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/Rollout.java
+++ b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/Rollout.java
@@ -38,7 +38,7 @@ public interface Rollout extends NamedEntity {
     void setDistributionSet(DistributionSet distributionSet);
 
     /**
-     * @return list of deployment groups of the rollout.
+     * @return immutable list of deployment groups of the rollout.
      */
     List<RolloutGroup> getRolloutGroups();
 
diff --git a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/SoftwareModule.java b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/SoftwareModule.java
index 3c3a24fd0..e3bf1468f 100644
--- a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/SoftwareModule.java
+++ b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/SoftwareModule.java
@@ -11,6 +11,10 @@ package org.eclipse.hawkbit.repository.model;
 import java.util.List;
 import java.util.Optional;
 
+/**
+ * Software package as sub element of a {@link DistributionSet}.
+ *
+ */
 public interface SoftwareModule extends NamedVersionedEntity {
 
     /**
@@ -40,12 +44,12 @@ public interface SoftwareModule extends NamedVersionedEntity {
     Optional<LocalArtifact> getLocalArtifactByFilename(String fileName);
 
     /**
-     * @return the artifacts
+     * @return immutable list of all artifacts
      */
     List<Artifact> getArtifacts();
 
     /**
-     * @return local artifacts only
+     * @return immutable list of local artifacts only
      */
     List<LocalArtifact> getLocalArtifacts();
 
@@ -104,7 +108,8 @@ public interface SoftwareModule extends NamedVersionedEntity {
     List<SoftwareModuleMetadata> getMetadata();
 
     /**
-     * @return the assignedTo
+     * @return immutable list of {@link DistributionSet}s the module is assigned
+     *         to
      */
     List<DistributionSet> getAssignedTo();
 
diff --git a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/Target.java b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/Target.java
index c09b28a2f..c07a8c224 100644
--- a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/Target.java
+++ b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/Target.java
@@ -32,12 +32,12 @@ public interface Target extends NamedEntity {
     String getControllerId();
 
     /**
-     * @return assigned {@link TargetTag}s.
+     * @return immutable set of assigned {@link TargetTag}s.
      */
     Set<TargetTag> getTags();
 
     /**
-     * @return {@link Action} history of the {@link Target}.
+     * @return immutable {@link Action} history of the {@link Target}.
      */
     List<Action> getActions();
 
@@ -64,4 +64,19 @@ public interface Target extends NamedEntity {
      */
     void setSecurityToken(String token);
 
+    /**
+     * @param tag
+     *            to add
+     * @return <code>true</code> if tag could be added sucessfully (i.e. was not
+     *         already in the list).
+     */
+    public boolean addTag(TargetTag tag);
+
+    /**
+     * @param tag
+     *            to remove
+     * @return <code>true</code> if tag was in the list and removed
+     */
+    public boolean removeTag(TargetTag tag);
+
 }
diff --git a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/TargetTag.java b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/TargetTag.java
index f222e9e90..afe0ff59a 100644
--- a/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/TargetTag.java
+++ b/hawkbit-repository/hawkbit-repository-api/src/main/java/org/eclipse/hawkbit/repository/model/TargetTag.java
@@ -17,7 +17,7 @@ import java.util.List;
 public interface TargetTag extends Tag {
 
     /**
-     * @return {@link List} of targets assigned to this {@link Tag}.
+     * @return immutable {@link List} of targets assigned to this {@link Tag}.
      */
     List<Target> getAssignedToTargets();
 
diff --git a/hawkbit-repository/hawkbit-repository-jpa/src/main/java/org/eclipse/hawkbit/repository/jpa/JpaTargetManagement.java b/hawkbit-repository/hawkbit-repository-jpa/src/main/java/org/eclipse/hawkbit/repository/jpa/JpaTargetManagement.java
index 67c28216d..b9085c601 100644
--- a/hawkbit-repository/hawkbit-repository-jpa/src/main/java/org/eclipse/hawkbit/repository/jpa/JpaTargetManagement.java
+++ b/hawkbit-repository/hawkbit-repository-jpa/src/main/java/org/eclipse/hawkbit/repository/jpa/JpaTargetManagement.java
@@ -343,7 +343,7 @@ public class JpaTargetManagement implements TargetManagement {
 
         // all are already assigned -> unassign
         if (alreadyAssignedTargets.size() == allTargets.size()) {
-            alreadyAssignedTargets.forEach(target -> ((JpaTarget) target).removeTag(tag));
+            alreadyAssignedTargets.forEach(target -> target.removeTag(tag));
             final TargetTagAssignmentResult result = new TargetTagAssignmentResult(0, 0, alreadyAssignedTargets.size(),
                     Collections.emptyList(), alreadyAssignedTargets, tag);
 
@@ -385,6 +385,7 @@ public class JpaTargetManagement implements TargetManagement {
     }
 
     private List<Target> unAssignTag(final Collection<Target> targets, final TargetTag tag) {
+        @SuppressWarnings({ "unchecked", "rawtypes" })
         final Collection<JpaTarget> toUnassign = (Collection) targets;
 
         toUnassign.forEach(target -> target.removeTag(tag));