diff --git a/hurricane/src/hurricane/DataBase.cpp b/hurricane/src/hurricane/DataBase.cpp
index abbbadde..64e9c818 100644
--- a/hurricane/src/hurricane/DataBase.cpp
+++ b/hurricane/src/hurricane/DataBase.cpp
@@ -53,6 +53,8 @@ void DataBase::_postCreate()
 void DataBase::_preDestroy()
 // ************************
 {
+  cerr << "DataBase::_preDestroy()" << endl;
+
     UpdateSession::open();
     Inherit::_preDestroy();
 
diff --git a/hurricane/src/hurricane/Layer.cpp b/hurricane/src/hurricane/Layer.cpp
index b348c771..62712475 100644
--- a/hurricane/src/hurricane/Layer.cpp
+++ b/hurricane/src/hurricane/Layer.cpp
@@ -202,10 +202,10 @@ namespace Hurricane {
 
   void Layer::_preDestroy ()
   {
-    DBo::_preDestroy();
-
     _technology->_getLayerMaskMap().erase(_mask);
     _technology->_getLayerMap()._remove(this);
+
+    DBo::_preDestroy ();
   }
 
 
diff --git a/hurricane/src/hurricane/NetExternalComponents.cpp b/hurricane/src/hurricane/NetExternalComponents.cpp
index 2c00288e..5657019f 100644
--- a/hurricane/src/hurricane/NetExternalComponents.cpp
+++ b/hurricane/src/hurricane/NetExternalComponents.cpp
@@ -9,17 +9,16 @@
 // ****************************************************************************************************
 
 #include "hurricane/Error.h"
-#include "hurricane/Relation.h"
 #include "hurricane/Net.h"
 
 #include "hurricane/NetExternalComponents.h"
 
 namespace Hurricane {
 
-static Name ExternalComponentsRelationName("ExternalComponentsRelation");
+  const Name NetExternalComponents::_name = "ExternalComponentsRelation";
 
-static StandardRelation* getExternalComponentsRelation(const Net* net) {
-    Property* property = net->getProperty(ExternalComponentsRelationName);
+  StandardRelation* NetExternalComponents::getRelation(const Net* net) {
+    Property* property = net->getProperty(_name);
     if (!property) {
         return NULL;
     } else {
@@ -35,7 +34,7 @@ Components NetExternalComponents::get(const Net* net) {
         throw Error("Impossible to retrieve external components on non external net "
                 + net->getName()._getString());
     
-    StandardRelation* externalComponentsRelation = getExternalComponentsRelation(net);
+    StandardRelation* externalComponentsRelation = getRelation(net);
     if (!externalComponentsRelation)
         return Components();
     return externalComponentsRelation->getSlaveOwners().getSubSet<Component*>();
@@ -46,9 +45,9 @@ void NetExternalComponents::setExternal(Component* component) {
     if (!net->isExternal())
         throw Error("Impossible to set as external a component member of non external net "
                 + net->getName()._getString());
-    StandardRelation* externalComponentsRelation = getExternalComponentsRelation(net);
+    StandardRelation* externalComponentsRelation = getRelation(net);
     if (!externalComponentsRelation)
-        externalComponentsRelation = StandardRelation::create(net, ExternalComponentsRelationName);
+        externalComponentsRelation = StandardRelation::create(net, _name);
     component->put(externalComponentsRelation);
 }
 
diff --git a/hurricane/src/hurricane/Technology.cpp b/hurricane/src/hurricane/Technology.cpp
index 4835b235..ebbab660 100644
--- a/hurricane/src/hurricane/Technology.cpp
+++ b/hurricane/src/hurricane/Technology.cpp
@@ -311,11 +311,14 @@ void Technology::_postCreate()
 void Technology::_preDestroy()
 // **************************
 {
-    Inherit::_preDestroy();
 
-    for_each_layer(layer, getLayers()) layer->destroy(); end_for;
+    while ( !_layerMap.isEmpty() ) {
+      _layerMap.getElements().getFirst()->destroy();
+    }
+  //for_each_layer(layer, getLayers()) layer->destroy(); end_for;
 
     _dataBase->_setTechnology(NULL);
+    DBo::_preDestroy();
 }
 
 void Technology::_insertInLayerMaskMap ( Layer* layer )
diff --git a/hurricane/src/hurricane/hurricane/NetExternalComponents.h b/hurricane/src/hurricane/hurricane/NetExternalComponents.h
index 7dc8435d..63e5197b 100644
--- a/hurricane/src/hurricane/hurricane/NetExternalComponents.h
+++ b/hurricane/src/hurricane/hurricane/NetExternalComponents.h
@@ -12,14 +12,19 @@
 #define HURRICANE_NET_EXTERNAL_COMPONENTS
 
 #include "hurricane/Component.h"
+#include "hurricane/Relation.h"
 
 namespace Hurricane {
 
-class NetExternalComponents {
+  class NetExternalComponents {
     public:
-        static Components get(const Net* net);
-        static void setExternal(Component* component);
-};
+      static Components        get         ( const Net* );
+      static void              setExternal ( Component* );
+    protected:
+      static StandardRelation* getRelation ( const Net* );
+    private:
+      static const Name  _name;
+  };
 
 } // End of Hurricane namespace.