diff --git a/src/main/java/org/gcube/informationsystem/resourceregistry/resources/Access.java b/src/main/java/org/gcube/informationsystem/resourceregistry/resources/Access.java
index bd0ff36..e5cd142 100644
--- a/src/main/java/org/gcube/informationsystem/resourceregistry/resources/Access.java
+++ b/src/main/java/org/gcube/informationsystem/resourceregistry/resources/Access.java
@@ -14,8 +14,8 @@ import org.gcube.informationsystem.resourceregistry.api.Query;
 import org.gcube.informationsystem.resourceregistry.api.SchemaManagement;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.InvalidQueryException;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.ResourceRegistryException;
-import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.FacetNotFoundException;
-import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.ResourceNotFoundException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.facet.FacetNotFoundException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.resource.ResourceNotFoundException;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.schema.SchemaNotFoundException;
 import org.gcube.informationsystem.resourceregistry.api.rest.AccessPath;
 import org.gcube.informationsystem.resourceregistry.resources.impl.EntityManagementImpl;
diff --git a/src/main/java/org/gcube/informationsystem/resourceregistry/resources/EntityManager.java b/src/main/java/org/gcube/informationsystem/resourceregistry/resources/EntityManager.java
index e5fbab0..5ca23db 100644
--- a/src/main/java/org/gcube/informationsystem/resourceregistry/resources/EntityManager.java
+++ b/src/main/java/org/gcube/informationsystem/resourceregistry/resources/EntityManager.java
@@ -19,8 +19,8 @@ import org.gcube.informationsystem.resourceregistry.api.EntityManagement;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.ResourceRegistryException;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.context.ContextNotFoundException;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.EntityException;
-import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.FacetNotFoundException;
-import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.ResourceNotFoundException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.facet.FacetNotFoundException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.resource.ResourceNotFoundException;
 import org.gcube.informationsystem.resourceregistry.api.rest.EntityPath;
 import org.gcube.informationsystem.resourceregistry.resources.impl.EntityManagementImpl;
 import org.gcube.informationsystem.resourceregistry.resources.utils.ContextUtility;
diff --git a/src/main/java/org/gcube/informationsystem/resourceregistry/resources/impl/EntityManagementImpl.java b/src/main/java/org/gcube/informationsystem/resourceregistry/resources/impl/EntityManagementImpl.java
index b5b96d9..f961a52 100644
--- a/src/main/java/org/gcube/informationsystem/resourceregistry/resources/impl/EntityManagementImpl.java
+++ b/src/main/java/org/gcube/informationsystem/resourceregistry/resources/impl/EntityManagementImpl.java
@@ -30,8 +30,12 @@ import org.gcube.informationsystem.resourceregistry.api.EntityManagement;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.ResourceRegistryException;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.context.ContextException;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.context.ContextNotFoundException;
-import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.FacetNotFoundException;
-import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.ResourceNotFoundException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.EntityAlreadyPresentException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.EntityNotFoundException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.facet.FacetAlreadyPresentException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.facet.FacetNotFoundException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.resource.ResourceAlreadyPresentException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.resource.ResourceNotFoundException;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.schema.SchemaNotFoundException;
 import org.gcube.informationsystem.resourceregistry.context.SecurityContextMapper;
 import org.gcube.informationsystem.resourceregistry.context.SecurityContextMapper.PermissionMode;
@@ -145,23 +149,30 @@ public class EntityManagementImpl implements EntityManagement {
 	protected Vertex getEntity(OrientGraph orientGraph, JsonNode jsonNode,
 			UUID uuid, Class<? extends Entity> entityClass)
 			throws JsonParseException, JsonMappingException, IOException,
-			FacetNotFoundException, ResourceNotFoundException,
-			ResourceRegistryException {
+			EntityNotFoundException, ResourceRegistryException {
 
 		String classProperty = getClassProperty(jsonNode);
 
 		try {
 			SchemaManagementImpl.getTypeSchema(orientGraph, classProperty,
-					classProperty);
+					entityClass.getSimpleName());
 		} catch (SchemaNotFoundException e) {
 			throw e;
 		}
 
 		Header header = HeaderUtility.getHeader(jsonNode, false);
-		UUID resourceUUID = header.getUUID();
+		if (header != null) {
+			UUID resourceUUID = header.getUUID();
+			if (resourceUUID.compareTo(uuid) != 0) {
+				String error = String
+						.format("UUID provided in header (%s) differs from the one (%s) used to identify the %s instance",
+								resourceUUID.toString(), uuid.toString(),
+								classProperty);
+				throw new ResourceRegistryException(error);
 
-		Vertex vertex = getEntity(orientGraph, resourceUUID, classProperty,
-				entityClass);
+			}
+		}
+		Vertex vertex = getEntity(orientGraph, uuid, classProperty, entityClass);
 
 		return vertex;
 	}
@@ -536,7 +547,8 @@ public class EntityManagementImpl implements EntityManagement {
 
 	private Vertex createVertexEntity(OrientGraph orientGraph,
 			String entityType, Class<? extends Entity> entity,
-			String jsonRepresentation) throws ResourceRegistryException {
+			String jsonRepresentation) throws EntityAlreadyPresentException,
+			ResourceRegistryException {
 
 		logger.trace("Going to create {} for {} ({}) using {}",
 				Vertex.class.getSimpleName(),
@@ -566,6 +578,29 @@ public class EntityManagementImpl implements EntityManagement {
 
 			OrientVertex vertex = orientGraph.addVertex("class:" + entityType);
 
+			try {
+				UUID uuid = org.gcube.informationsystem.impl.utils.Utility
+						.getUUIDFromJsonNode(jsonNode);
+				
+				Vertex v = getEntity(orientGraph, jsonNode, uuid, entity);
+				if(v!=null){
+					String error = String.format("An %s with UUID %s already exist", entity.getSimpleName(), uuid.toString());
+					if (Facet.class.isAssignableFrom(entity)) {
+						throw new FacetAlreadyPresentException(error);
+					}
+					if (Resource.class.isAssignableFrom(entity)) {
+						throw new ResourceAlreadyPresentException(error);
+					}
+					
+					throw new EntityAlreadyPresentException(error);
+				}
+				 
+			} catch (EntityAlreadyPresentException e) {
+				throw e;
+			} catch (Exception e) {
+				// no header or no header with uuid is provided and it is fine
+			}
+
 			Header entityHeader = HeaderUtility.getHeader(jsonNode, true);
 			if (entityHeader != null) {
 				vertex.setProperty(Entity.HEADER_PROPERTY, entityHeader);
@@ -600,7 +635,8 @@ public class EntityManagementImpl implements EntityManagement {
 					Utility.toJsonString((OrientVertex) vertex, true));
 
 			return vertex;
-
+		} catch (ResourceRegistryException e) {
+			throw e;
 		} catch (Exception e) {
 			logger.trace("Error while creating {} for {} ({}) using {}",
 					Vertex.class.getSimpleName(), entity.getClass()
@@ -787,7 +823,7 @@ public class EntityManagementImpl implements EntityManagement {
 
 	@Override
 	public String createFacet(String facetType, String jsonRepresentation)
-			throws ResourceRegistryException {
+			throws FacetAlreadyPresentException, ResourceRegistryException {
 		OrientGraph orientGraph = null;
 
 		try {
@@ -1161,7 +1197,7 @@ public class EntityManagementImpl implements EntityManagement {
 
 	@Override
 	public String createResource(String resourceType, String jsonRepresentation)
-			throws ResourceRegistryException {
+			throws ResourceAlreadyPresentException, ResourceRegistryException {
 
 		logger.debug("Trying to create {} using {}", resourceType,
 				jsonRepresentation);
@@ -1415,15 +1451,30 @@ public class EntityManagementImpl implements EntityManagement {
 		}
 	}
 
+	@Override
 	public boolean addResourceToContext(UUID uuid)
 			throws ResourceNotFoundException, ContextNotFoundException,
 			ResourceRegistryException {
 		return addEntityToContext(Resource.class, uuid);
 	}
 
+	@Override
 	public boolean addFacetToContext(UUID uuid) throws FacetNotFoundException,
 			ContextNotFoundException, ResourceRegistryException {
 		return addEntityToContext(Facet.class, uuid);
 	}
 
+	@Override
+	public boolean removeResourceFromContext(UUID uuid)
+			throws ResourceNotFoundException, ContextNotFoundException,
+			ResourceRegistryException {
+		throw new UnsupportedOperationException();
+	}
+
+	@Override
+	public boolean removeFacetFromContext(UUID uuid)
+			throws FacetNotFoundException, ContextNotFoundException,
+			ResourceRegistryException {
+		throw new UnsupportedOperationException();
+	}
 }
diff --git a/src/main/java/org/gcube/informationsystem/resourceregistry/resources/utils/HeaderUtility.java b/src/main/java/org/gcube/informationsystem/resourceregistry/resources/utils/HeaderUtility.java
index fc07703..3aee908 100644
--- a/src/main/java/org/gcube/informationsystem/resourceregistry/resources/utils/HeaderUtility.java
+++ b/src/main/java/org/gcube/informationsystem/resourceregistry/resources/utils/HeaderUtility.java
@@ -78,6 +78,8 @@ public class HeaderUtility {
 			}
 			HeaderOrient header = null;
 			if(creation){
+				// If an header is provided MUST contains and UUID otherwise is
+				// an invalid request so that let that an exception is raised
 				UUID uuid = UUID.fromString(headerNode.get(Header.UUID_PROPERTY).asText());
 				header = (HeaderOrient) createHeader(uuid);
 			}else{
diff --git a/src/test/java/org/gcube/informationsystem/resourceregistry/EntityManagementFactory.java b/src/test/java/org/gcube/informationsystem/resourceregistry/EntityManagementFactory.java
index ef443c6..bf920a9 100644
--- a/src/test/java/org/gcube/informationsystem/resourceregistry/EntityManagementFactory.java
+++ b/src/test/java/org/gcube/informationsystem/resourceregistry/EntityManagementFactory.java
@@ -5,8 +5,8 @@ import java.util.UUID;
 import org.gcube.informationsystem.resourceregistry.api.EntityManagement;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.ResourceRegistryException;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.context.ContextNotFoundException;
-import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.FacetNotFoundException;
-import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.ResourceNotFoundException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.facet.FacetNotFoundException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.resource.ResourceNotFoundException;
 import org.glassfish.hk2.api.Factory;
 
 public class EntityManagementFactory implements Factory<EntityManagement> {
@@ -129,6 +129,22 @@ public class EntityManagementFactory implements Factory<EntityManagement> {
 				return null;
 			}
 
+			@Override
+			public boolean removeResourceFromContext(UUID uuid)
+					throws ResourceNotFoundException, ContextNotFoundException,
+					ResourceRegistryException {
+				// TODO Auto-generated method stub
+				return false;
+			}
+
+			@Override
+			public boolean removeFacetFromContext(UUID uuid)
+					throws FacetNotFoundException, ContextNotFoundException,
+					ResourceRegistryException {
+				// TODO Auto-generated method stub
+				return false;
+			}
+
 		};
 	}
 
diff --git a/src/test/java/org/gcube/informationsystem/resourceregistry/resources/impl/EntityManagementImplTest.java b/src/test/java/org/gcube/informationsystem/resourceregistry/resources/impl/EntityManagementImplTest.java
index c4e6d0b..0d6f7c3 100644
--- a/src/test/java/org/gcube/informationsystem/resourceregistry/resources/impl/EntityManagementImplTest.java
+++ b/src/test/java/org/gcube/informationsystem/resourceregistry/resources/impl/EntityManagementImplTest.java
@@ -43,7 +43,7 @@ import org.gcube.informationsystem.model.relation.ConsistsOf;
 import org.gcube.informationsystem.model.relation.IsIdentifiedBy;
 import org.gcube.informationsystem.model.relation.Relation;
 import org.gcube.informationsystem.model.relation.isrelatedto.Hosts;
-import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.FacetNotFoundException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.facet.FacetNotFoundException;
 import org.junit.Assert;
 import org.junit.Test;
 import org.slf4j.Logger;
diff --git a/src/test/java/org/gcube/informationsystem/resourceregistry/resources/impl/MultiContextTest.java b/src/test/java/org/gcube/informationsystem/resourceregistry/resources/impl/MultiContextTest.java
index 2258dff..1ee6327 100644
--- a/src/test/java/org/gcube/informationsystem/resourceregistry/resources/impl/MultiContextTest.java
+++ b/src/test/java/org/gcube/informationsystem/resourceregistry/resources/impl/MultiContextTest.java
@@ -42,7 +42,7 @@ import org.gcube.informationsystem.model.relation.consistsof.HasVolatileMemory;
 import org.gcube.informationsystem.model.relation.isrelatedto.Hosts;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.ResourceRegistryException;
 import org.gcube.informationsystem.resourceregistry.api.exceptions.context.ContextNotFoundException;
-import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.ResourceNotFoundException;
+import org.gcube.informationsystem.resourceregistry.api.exceptions.entity.resource.ResourceNotFoundException;
 import org.junit.Assert;
 import org.junit.Test;
 import org.slf4j.Logger;