diff --git a/li.strolch.agent/src/main/java/li/strolch/agent/api/ElementMap.java b/li.strolch.agent/src/main/java/li/strolch/agent/api/ElementMap.java
index 28f88461a..398ae3e9f 100644
--- a/li.strolch.agent/src/main/java/li/strolch/agent/api/ElementMap.java
+++ b/li.strolch.agent/src/main/java/li/strolch/agent/api/ElementMap.java
@@ -65,7 +65,7 @@ public interface ElementMap<T extends StrolchRootElement> {
 	public T getBy(StrolchTransaction tx, String type, String id);
 
 	/**
-	 * Returns the Element which is referenced by the given {@link StringParameter}. A reference {@link Parameter} must
+	 * Returns the element which is referenced by the given {@link StringParameter}. A reference {@link Parameter} must
 	 * have its interpretation set to the element type being referenced e.g. s
 	 * {@link StrolchConstants#INTERPRETATION_ORDER_REF} and the UOM must be set to the element's type and the value is
 	 * the id of the element
@@ -74,12 +74,15 @@ public interface ElementMap<T extends StrolchRootElement> {
 	 *            the {@link StrolchTransaction} instance
 	 * @param refP
 	 *            the {@link StringParameter} which references an element
+	 * @param assertExists
+	 *            if true, and element does not exist, then a {@link StrolchException} is thrown
+	 * 
 	 * @return the element found, or null if it does not exist
 	 * 
 	 * @throws StrolchException
 	 *             if the {@link StringParameter} is not a properly configured as a reference parameter
 	 */
-	public T getBy(StrolchTransaction tx, StringParameter refP) throws StrolchException;
+	public T getBy(StrolchTransaction tx, StringParameter refP, boolean assertExists) throws StrolchException;
 
 	/**
 	 * Returns all elements which are referenced by the given {@link StringListParameter}. A reference {@link Parameter}
@@ -91,6 +94,8 @@ public interface ElementMap<T extends StrolchRootElement> {
 	 *            the {@link StrolchTransaction} instance
 	 * @param refP
 	 *            the {@link StringListParameter} which references an element
+	 * @param assertExists
+	 *            if true, and element does not exist, then a {@link StrolchException} is thrown
 	 * 
 	 * @return the list of elements found, or the empty list if they do not exist. <b>Note:</b> Any missing elements are
 	 *         not returned!
@@ -98,7 +103,7 @@ public interface ElementMap<T extends StrolchRootElement> {
 	 * @throws StrolchException
 	 *             if the {@link StringParameter} is not a properly configured as a reference parameter
 	 */
-	public List<T> getBy(StrolchTransaction tx, StringListParameter refP) throws StrolchException;
+	public List<T> getBy(StrolchTransaction tx, StringListParameter refP, boolean assertExists) throws StrolchException;
 
 	public List<T> getAllElements(StrolchTransaction tx);
 
diff --git a/li.strolch.agent/src/main/java/li/strolch/agent/impl/AuditingElementMapFacade.java b/li.strolch.agent/src/main/java/li/strolch/agent/impl/AuditingElementMapFacade.java
index 479b4c783..7a5ef552d 100644
--- a/li.strolch.agent/src/main/java/li/strolch/agent/impl/AuditingElementMapFacade.java
+++ b/li.strolch.agent/src/main/java/li/strolch/agent/impl/AuditingElementMapFacade.java
@@ -105,57 +105,26 @@ public class AuditingElementMapFacade<T extends StrolchRootElement> implements E
 		return this.deletedAllByType;
 	}
 
-	/**
-	 * @param tx
-	 * @param type
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#hasType(li.strolch.persistence.api.StrolchTransaction, java.lang.String)
-	 */
 	@Override
 	public boolean hasType(StrolchTransaction tx, String type) {
 		return this.elementMap.hasType(tx, type);
 	}
 
-	/**
-	 * @param tx
-	 * @param type
-	 * @param id
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#hasElement(li.strolch.persistence.api.StrolchTransaction, java.lang.String,
-	 *      java.lang.String)
-	 */
 	@Override
 	public boolean hasElement(StrolchTransaction tx, String type, String id) {
 		return this.elementMap.hasElement(tx, type, id);
 	}
 
-	/**
-	 * @param tx
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#querySize(li.strolch.persistence.api.StrolchTransaction)
-	 */
 	@Override
 	public long querySize(StrolchTransaction tx) {
 		return this.elementMap.querySize(tx);
 	}
 
-	/**
-	 * @param tx
-	 * @param type
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#querySize(li.strolch.persistence.api.StrolchTransaction, java.lang.String)
-	 */
 	@Override
 	public long querySize(StrolchTransaction tx, String type) {
 		return this.elementMap.querySize(tx, type);
 	}
 
-	/**
-	 * @param tx
-	 * @param type
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#getTemplate(li.strolch.persistence.api.StrolchTransaction, java.lang.String)
-	 */
 	@Override
 	public T getTemplate(StrolchTransaction tx, String type) {
 		T template = this.elementMap.getTemplate(tx, type);
@@ -164,14 +133,6 @@ public class AuditingElementMapFacade<T extends StrolchRootElement> implements E
 		return template;
 	}
 
-	/**
-	 * @param tx
-	 * @param type
-	 * @param id
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#getBy(li.strolch.persistence.api.StrolchTransaction, java.lang.String,
-	 *      java.lang.String)
-	 */
 	@Override
 	public T getBy(StrolchTransaction tx, String type, String id) {
 		T element = this.elementMap.getBy(tx, type, id);
@@ -180,35 +141,22 @@ public class AuditingElementMapFacade<T extends StrolchRootElement> implements E
 		return element;
 	}
 
-	/**
-	 * @param tx
-	 * @param refP
-	 * @return
-	 * @throws StrolchException
-	 * @see li.strolch.agent.api.ElementMap#getBy(li.strolch.persistence.api.StrolchTransaction,
-	 *      li.strolch.model.parameter.StringParameter)
-	 */
 	@Override
-	public T getBy(StrolchTransaction tx, StringParameter refP) throws StrolchException {
-		T element = this.elementMap.getBy(tx, refP);
+	public T getBy(StrolchTransaction tx, StringParameter refP, boolean assertExists) throws StrolchException {
+		T element = this.elementMap.getBy(tx, refP, assertExists);
 		if (this.observeAccessReads)
 			this.read.add(element);
 		return element;
 	}
 
 	@Override
-	public List<T> getBy(StrolchTransaction tx, StringListParameter refP) throws StrolchException {
-		List<T> elements = this.elementMap.getBy(tx, refP);
+	public List<T> getBy(StrolchTransaction tx, StringListParameter refP, boolean assertExists) throws StrolchException {
+		List<T> elements = this.elementMap.getBy(tx, refP, assertExists);
 		if (this.observeAccessReads)
 			this.read.addAll(elements);
 		return elements;
 	}
 
-	/**
-	 * @param tx
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#getAllElements(li.strolch.persistence.api.StrolchTransaction)
-	 */
 	@Override
 	public List<T> getAllElements(StrolchTransaction tx) {
 		List<T> elements = this.elementMap.getAllElements(tx);
@@ -217,13 +165,6 @@ public class AuditingElementMapFacade<T extends StrolchRootElement> implements E
 		return elements;
 	}
 
-	/**
-	 * @param tx
-	 * @param type
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#getElementsBy(li.strolch.persistence.api.StrolchTransaction,
-	 *      java.lang.String)
-	 */
 	@Override
 	public List<T> getElementsBy(StrolchTransaction tx, String type) {
 		List<T> elements = this.elementMap.getElementsBy(tx, type);
@@ -232,67 +173,33 @@ public class AuditingElementMapFacade<T extends StrolchRootElement> implements E
 		return elements;
 	}
 
-	/**
-	 * @param tx
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#getTypes(li.strolch.persistence.api.StrolchTransaction)
-	 */
 	@Override
 	public Set<String> getTypes(StrolchTransaction tx) {
 		return this.elementMap.getTypes(tx);
 	}
 
-	/**
-	 * @param tx
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#getAllKeys(li.strolch.persistence.api.StrolchTransaction)
-	 */
 	@Override
 	public Set<String> getAllKeys(StrolchTransaction tx) {
 		return this.elementMap.getAllKeys(tx);
 	}
 
-	/**
-	 * @param tx
-	 * @param type
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#getKeysBy(li.strolch.persistence.api.StrolchTransaction, java.lang.String)
-	 */
 	@Override
 	public Set<String> getKeysBy(StrolchTransaction tx, String type) {
 		return this.elementMap.getKeysBy(tx, type);
 	}
 
-	/**
-	 * @param tx
-	 * @param element
-	 * @see li.strolch.agent.api.ElementMap#add(li.strolch.persistence.api.StrolchTransaction,
-	 *      li.strolch.model.StrolchRootElement)
-	 */
 	@Override
 	public void add(StrolchTransaction tx, T element) {
 		this.elementMap.add(tx, element);
 		this.created.add(element);
 	}
 
-	/**
-	 * @param tx
-	 * @param elements
-	 * @see li.strolch.agent.api.ElementMap#addAll(li.strolch.persistence.api.StrolchTransaction, java.util.List)
-	 */
 	@Override
 	public void addAll(StrolchTransaction tx, List<T> elements) {
 		this.elementMap.addAll(tx, elements);
 		this.created.addAll(elements);
 	}
 
-	/**
-	 * @param tx
-	 * @param element
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#update(li.strolch.persistence.api.StrolchTransaction,
-	 *      li.strolch.model.StrolchRootElement)
-	 */
 	@Override
 	public T update(StrolchTransaction tx, T element) {
 		T replaced = this.elementMap.update(tx, element);
@@ -301,12 +208,6 @@ public class AuditingElementMapFacade<T extends StrolchRootElement> implements E
 
 	}
 
-	/**
-	 * @param tx
-	 * @param elements
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#updateAll(li.strolch.persistence.api.StrolchTransaction, java.util.List)
-	 */
 	@Override
 	public List<T> updateAll(StrolchTransaction tx, List<T> elements) {
 		List<T> replaced = this.elementMap.updateAll(tx, elements);
@@ -314,34 +215,18 @@ public class AuditingElementMapFacade<T extends StrolchRootElement> implements E
 		return replaced;
 	}
 
-	/**
-	 * @param tx
-	 * @param element
-	 * @see li.strolch.agent.api.ElementMap#remove(li.strolch.persistence.api.StrolchTransaction,
-	 *      li.strolch.model.StrolchRootElement)
-	 */
 	@Override
 	public void remove(StrolchTransaction tx, T element) {
 		this.elementMap.remove(tx, element);
 		this.deleted.add(element);
 	}
 
-	/**
-	 * @param tx
-	 * @param elements
-	 * @see li.strolch.agent.api.ElementMap#removeAll(li.strolch.persistence.api.StrolchTransaction, java.util.List)
-	 */
 	@Override
 	public void removeAll(StrolchTransaction tx, List<T> elements) {
 		this.elementMap.removeAll(tx, elements);
 		this.deleted.addAll(elements);
 	}
 
-	/**
-	 * @param tx
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#removeAll(li.strolch.persistence.api.StrolchTransaction)
-	 */
 	@Override
 	public long removeAll(StrolchTransaction tx) {
 		long removed = this.elementMap.removeAll(tx);
@@ -349,12 +234,6 @@ public class AuditingElementMapFacade<T extends StrolchRootElement> implements E
 		return removed;
 	}
 
-	/**
-	 * @param tx
-	 * @param type
-	 * @return
-	 * @see li.strolch.agent.api.ElementMap#removeAllBy(li.strolch.persistence.api.StrolchTransaction, java.lang.String)
-	 */
 	@Override
 	public long removeAllBy(StrolchTransaction tx, String type) {
 		long removed = this.elementMap.removeAllBy(tx, type);
diff --git a/li.strolch.agent/src/main/java/li/strolch/agent/impl/CachedElementMap.java b/li.strolch.agent/src/main/java/li/strolch/agent/impl/CachedElementMap.java
index d6fd1dfc3..2f28bc4b3 100644
--- a/li.strolch.agent/src/main/java/li/strolch/agent/impl/CachedElementMap.java
+++ b/li.strolch.agent/src/main/java/li/strolch/agent/impl/CachedElementMap.java
@@ -107,15 +107,21 @@ public abstract class CachedElementMap<T extends StrolchRootElement> implements
 	protected abstract void assertIsRefParam(Parameter<?> refP);
 
 	@Override
-	public T getBy(StrolchTransaction tx, StringParameter refP) throws StrolchException {
+	public T getBy(StrolchTransaction tx, StringParameter refP, boolean assertExists) throws StrolchException {
 		assertIsRefParam(refP);
 		String type = refP.getUom();
 		String id = refP.getValue();
-		return getBy(tx, type, id);
+		T element = getBy(tx, type, id);
+		if (assertExists && element == null) {
+			String msg = "The element for refP {0} with id {1} does not exist!"; //$NON-NLS-1$
+			msg = MessageFormat.format(msg, refP.getLocator(), id);
+			throw new StrolchException(msg);
+		}
+		return element;
 	}
 
 	@Override
-	public List<T> getBy(StrolchTransaction tx, StringListParameter refP) throws StrolchException {
+	public List<T> getBy(StrolchTransaction tx, StringListParameter refP, boolean assertExists) throws StrolchException {
 		assertIsRefParam(refP);
 
 		List<T> elements = new ArrayList<>();
@@ -124,8 +130,15 @@ public abstract class CachedElementMap<T extends StrolchRootElement> implements
 
 		for (String id : ids) {
 			T element = getBy(tx, type, id);
-			if (element != null)
+			if (element != null) {
 				elements.add(element);
+			} else if (assertExists) {
+				if (assertExists && element == null) {
+					String msg = "The element for refP {0} with id {1} does not exist!"; //$NON-NLS-1$
+					msg = MessageFormat.format(msg, refP.getLocator(), id);
+					throw new StrolchException(msg);
+				}
+			}
 		}
 
 		return elements;
diff --git a/li.strolch.agent/src/main/java/li/strolch/agent/impl/TransactionalElementMap.java b/li.strolch.agent/src/main/java/li/strolch/agent/impl/TransactionalElementMap.java
index 59f52b50a..ef00f1cf2 100644
--- a/li.strolch.agent/src/main/java/li/strolch/agent/impl/TransactionalElementMap.java
+++ b/li.strolch.agent/src/main/java/li/strolch/agent/impl/TransactionalElementMap.java
@@ -1,5 +1,6 @@
 package li.strolch.agent.impl;
 
+import java.text.MessageFormat;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Set;
@@ -56,15 +57,21 @@ public abstract class TransactionalElementMap<T extends StrolchRootElement> impl
 	protected abstract void assertIsRefParam(Parameter<?> refP);
 
 	@Override
-	public T getBy(StrolchTransaction tx, StringParameter refP) throws StrolchException {
+	public T getBy(StrolchTransaction tx, StringParameter refP, boolean assertExists) throws StrolchException {
 		assertIsRefParam(refP);
 		String type = refP.getUom();
 		String id = refP.getValue();
-		return getBy(tx, type, id);
+		T element = getBy(tx, type, id);
+		if (assertExists && element == null) {
+			String msg = "The element for refP {0} with id {1} does not exist!"; //$NON-NLS-1$
+			msg = MessageFormat.format(msg, refP.getLocator(), id);
+			throw new StrolchException(msg);
+		}
+		return element;
 	}
 
 	@Override
-	public List<T> getBy(StrolchTransaction tx, StringListParameter refP) throws StrolchException {
+	public List<T> getBy(StrolchTransaction tx, StringListParameter refP, boolean assertExists) throws StrolchException {
 		assertIsRefParam(refP);
 
 		List<T> elements = new ArrayList<>();
@@ -73,8 +80,15 @@ public abstract class TransactionalElementMap<T extends StrolchRootElement> impl
 
 		for (String id : ids) {
 			T element = getBy(tx, type, id);
-			if (element != null)
+			if (element != null) {
 				elements.add(element);
+			} else if (assertExists) {
+				if (assertExists && element == null) {
+					String msg = "The element for refP {0} with id {1} does not exist!"; //$NON-NLS-1$
+					msg = MessageFormat.format(msg, refP.getLocator(), id);
+					throw new StrolchException(msg);
+				}
+			}
 		}
 
 		return elements;
diff --git a/li.strolch.agent/src/main/java/li/strolch/persistence/api/AbstractTransaction.java b/li.strolch.agent/src/main/java/li/strolch/persistence/api/AbstractTransaction.java
index 9ec9ae206..ce99a91a4 100644
--- a/li.strolch.agent/src/main/java/li/strolch/persistence/api/AbstractTransaction.java
+++ b/li.strolch.agent/src/main/java/li/strolch/persistence/api/AbstractTransaction.java
@@ -395,17 +395,17 @@ public abstract class AbstractTransaction implements StrolchTransaction {
 
 	@Override
 	public Order getOrderBy(StringParameter refP, boolean assertExists) throws StrolchException {
-		Order order = getOrderMap().getBy(this, refP);
-		if (assertExists && order == null) {
-			String msg = "No Order exists with the id {0} with type {1} for refP {2}";
-			throw new StrolchException(MessageFormat.format(msg, refP.getValue(), refP.getUom(), refP.getLocator()));
-		}
-		return order;
+		return getOrderMap().getBy(this, refP, assertExists);
 	}
 
 	@Override
 	public List<Order> getOrdersBy(StringListParameter refP) throws StrolchException {
-		return getOrderMap().getBy(this, refP);
+		return getOrderMap().getBy(this, refP, false);
+	}
+
+	@Override
+	public List<Order> getOrdersBy(StringListParameter refP, boolean assertExists) throws StrolchException {
+		return getOrderMap().getBy(this, refP, assertExists);
 	}
 
 	@Override
@@ -430,17 +430,17 @@ public abstract class AbstractTransaction implements StrolchTransaction {
 
 	@Override
 	public Resource getResourceBy(StringParameter refP, boolean assertExists) throws StrolchException {
-		Resource resource = getResourceMap().getBy(this, refP);
-		if (assertExists && resource == null) {
-			String msg = "No Resource exists with the id {0} with type {1} for refP {2}";
-			throw new StrolchException(MessageFormat.format(msg, refP.getValue(), refP.getUom(), refP.getLocator()));
-		}
-		return resource;
+		return getResourceMap().getBy(this, refP, assertExists);
 	}
 
 	@Override
 	public List<Resource> getResourcesBy(StringListParameter refP) throws StrolchException {
-		return getResourceMap().getBy(this, refP);
+		return getResourceMap().getBy(this, refP, false);
+	}
+
+	@Override
+	public List<Resource> getResourcesBy(StringListParameter refP, boolean assertExists) throws StrolchException {
+		return getResourceMap().getBy(this, refP, assertExists);
 	}
 
 	@Override
diff --git a/li.strolch.agent/src/main/java/li/strolch/persistence/api/StrolchTransaction.java b/li.strolch.agent/src/main/java/li/strolch/persistence/api/StrolchTransaction.java
index 1edd1aa80..0f4743806 100644
--- a/li.strolch.agent/src/main/java/li/strolch/persistence/api/StrolchTransaction.java
+++ b/li.strolch.agent/src/main/java/li/strolch/persistence/api/StrolchTransaction.java
@@ -580,6 +580,24 @@ public interface StrolchTransaction extends AutoCloseable {
 	 */
 	public List<Resource> getResourcesBy(StringListParameter refP) throws StrolchException;
 
+	/**
+	 * Returns all {@link Resource Resources} which are referenced by the given {@link StringListParameter}. A reference
+	 * {@link Parameter} must have its interpretation set to {@link StrolchConstants#INTERPRETATION_RESOURCE_REF} and
+	 * the UOM must be set to the resource's type and the value is the id of the resource
+	 * 
+	 * @param refP
+	 *            the {@link StringListParameter} which references a list of {@link Resource Resources}
+	 * @param assertExists
+	 *            if true, and resource does not exist, then a {@link StrolchException} is thrown
+	 * 
+	 * @return the resources referenced by the parameter, or the empty list if they do not exist. <b>Note:</b> Any
+	 *         missing resources are not returned!
+	 * 
+	 * @throws StrolchException
+	 *             if the {@link StringListParameter} is not a properly configured as a reference parameter
+	 */
+	public List<Resource> getResourcesBy(StringListParameter refP, boolean assertExists) throws StrolchException;
+
 	/**
 	 * Returns the {@link Order} with the given type and id, or null if it does not exist
 	 * 
@@ -657,4 +675,22 @@ public interface StrolchTransaction extends AutoCloseable {
 	 *             if the {@link StringListParameter} is not a properly configured as a reference parameter
 	 */
 	public List<Order> getOrdersBy(StringListParameter refP) throws StrolchException;
+
+	/**
+	 * Returns all {@link Order Orders} which are referenced by the given {@link StringListParameter}. A reference
+	 * {@link Parameter} must have its interpretation set to {@link StrolchConstants#INTERPRETATION_ORDER_REF} and the
+	 * UOM must be set to the order's type and the value is the id of the order
+	 * 
+	 * @param refP
+	 *            the {@link StringListParameter} which references a list of {@link Order Orders}
+	 * @param assertExists
+	 *            if true, and order does not exist, then a {@link StrolchException} is thrown
+	 * 
+	 * @return the orders referenced by the parameter, or the empty list if they do not exist. <b>Note:</b> Any missing
+	 *         orders are not returned!
+	 * 
+	 * @throws StrolchException
+	 *             if the {@link StringListParameter} is not a properly configured as a reference parameter
+	 */
+	public List<Order> getOrdersBy(StringListParameter refP, boolean assertExists) throws StrolchException;
 }