diff --git a/src/main/java/org/gcube/informationsystem/discovery/RegistrationProvider.java b/src/main/java/org/gcube/informationsystem/discovery/RegistrationProvider.java
index 41cb96d..c34c553 100644
--- a/src/main/java/org/gcube/informationsystem/discovery/RegistrationProvider.java
+++ b/src/main/java/org/gcube/informationsystem/discovery/RegistrationProvider.java
@@ -8,6 +8,8 @@ import java.util.Collection;
  * returning the list of packages containing the interfaces
  * representing the model.
  * 
+ * Any registration provider MUST have a constructor with no arguments
+ * 
  * @author Luca Frosini (ISTI - CNR)
  */
 public interface RegistrationProvider {
diff --git a/src/main/java/org/gcube/informationsystem/discovery/knowledge/AddElementToTreeAction.java b/src/main/java/org/gcube/informationsystem/discovery/knowledge/AddElementToTreeAction.java
index 32b67b5..dee5550 100644
--- a/src/main/java/org/gcube/informationsystem/discovery/knowledge/AddElementToTreeAction.java
+++ b/src/main/java/org/gcube/informationsystem/discovery/knowledge/AddElementToTreeAction.java
@@ -3,9 +3,13 @@
  */
 package org.gcube.informationsystem.discovery.knowledge;
 
+import org.gcube.informationsystem.base.reference.AccessType;
 import org.gcube.informationsystem.base.reference.Element;
 import org.gcube.informationsystem.discovery.DiscoveredElementAction;
 import org.gcube.informationsystem.tree.Tree;
+import org.gcube.informationsystem.types.TypeMapper;
+import org.gcube.informationsystem.types.reference.Type;
+import org.gcube.informationsystem.types.reference.entities.ResourceType;
 
 /**
  * @author Luca Frosini (ISTI - CNR)
@@ -21,6 +25,19 @@ public class AddElementToTreeAction implements DiscoveredElementAction<Element>
 	@Override
 	public void analizeElement(Class<Element> e) throws Exception {
 		tree.addNode(e);
+		Type type = TypeMapper.createTypeDefinition(e);
+		createUsageKnowledge(type);
+	}
+	
+	protected void createUsageKnowledge(Type type) {
+		if (type.getAccessType() != AccessType.RESOURCE) {
+			return;
+		}
+		ResourceType rt = (ResourceType) type;
+		UsageKnowledge fk = UsageKnowledge.getFacetKnowledge();
+		fk.addAll(rt.getFacets());
+		UsageKnowledge rk = UsageKnowledge.getResourceKnowledge();
+		rk.addAll(rt.getResources());
 	}
 
 }
diff --git a/src/main/java/org/gcube/informationsystem/discovery/knowledge/ModelKnowledge.java b/src/main/java/org/gcube/informationsystem/discovery/knowledge/ModelKnowledge.java
index 0423e01..8ca876c 100644
--- a/src/main/java/org/gcube/informationsystem/discovery/knowledge/ModelKnowledge.java
+++ b/src/main/java/org/gcube/informationsystem/discovery/knowledge/ModelKnowledge.java
@@ -12,31 +12,46 @@ import org.gcube.informationsystem.discovery.Discovery;
 import org.gcube.informationsystem.discovery.RegistrationProvider;
 import org.gcube.informationsystem.serialization.ElementMappingAction;
 import org.gcube.informationsystem.tree.Tree;
-import org.gcube.informationsystem.types.TypeMapper;
-import org.gcube.informationsystem.types.knowledge.AddTypeToTreeAction;
-import org.gcube.informationsystem.types.knowledge.TypeInformation;
-import org.gcube.informationsystem.types.reference.Type;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /**
  * @author Luca Frosini (ISTI - CNR)
  */
 public class ModelKnowledge {
 	
+	private static final Logger logger = LoggerFactory.getLogger(ModelKnowledge.class);
+	
+	protected boolean created;
+	
 	public static ModelKnowledge getInstance() {
 		return new ModelKnowledge();
 	}
 	
 	protected Map<AccessType, Tree<Class<Element>>> trees;
-	protected Map<AccessType, Tree<Type>> typeTrees;
 	protected Map<AccessType, Discovery<? extends Element>> discoveries;
 	
 	protected ModelKnowledge() {
 		this.trees = new HashMap<>();
-		this.typeTrees = new HashMap<>();
 		this.discoveries = new HashMap<>();
+		this.created = false;
 	}
 	
-	public void createKnowledge() throws Exception {
+	public synchronized void createKnowledge(boolean force) throws Exception {
+		if(force) {
+			this.created = false;
+			logger.info("Going to force Knowledge recreation");
+		}
+		
+		createKnowledge();
+	}
+	
+	public synchronized void createKnowledge() throws Exception {	
+		
+		if(created) {
+			logger.trace("Knowledge has been already created.");
+			return;
+		}
 		
 		AccessType[] modelTypes = AccessType.getModelTypes();
 		
@@ -48,7 +63,6 @@ public class ModelKnowledge {
 		}
 		
 		ClassInformation classInformation = new ClassInformation();
-		TypeInformation typeInformation = new TypeInformation();
 		
 		for(AccessType accessType : modelTypes) {
 			
@@ -57,31 +71,22 @@ public class ModelKnowledge {
 			trees.put(accessType, tree);
 			AddElementToTreeAction aetta = new AddElementToTreeAction(tree);
 			
-			Type type = TypeMapper.createTypeDefinition(clz);
-			Tree<Type> typeTree = new Tree<>(type, typeInformation);
-			typeTrees.put(accessType, typeTree);
-			AddTypeToTreeAction attta = new AddTypeToTreeAction(typeTree);
-			
-			
 			Discovery<? extends Element> discovery = new Discovery<>(clz);
 			discoveries.put(accessType, discovery);
 			discovery.addPackages(allPackages);
 			discovery.addDiscoveredElementActions(new ElementMappingAction());
 			discovery.addDiscoveredElementActions(aetta);
-			discovery.addDiscoveredElementActions(attta);
 			
 			discovery.discover();
 			
 		}
 		
+		this.created = true;
+		
 	}
 	
-	public Tree<Class<Element>> getClassesTree(AccessType accessType) {
+	public synchronized Tree<Class<Element>> getClassesTree(AccessType accessType) {
 		return trees.get(accessType);
 	}
-
-	public Tree<Type> getTypesTree(AccessType accessType) {
-		return typeTrees.get(accessType);
-	}
 	
 }
diff --git a/src/main/java/org/gcube/informationsystem/types/knowledge/UsageKnowledge.java b/src/main/java/org/gcube/informationsystem/discovery/knowledge/UsageKnowledge.java
similarity index 96%
rename from src/main/java/org/gcube/informationsystem/types/knowledge/UsageKnowledge.java
rename to src/main/java/org/gcube/informationsystem/discovery/knowledge/UsageKnowledge.java
index 2e256a3..511c1d3 100644
--- a/src/main/java/org/gcube/informationsystem/types/knowledge/UsageKnowledge.java
+++ b/src/main/java/org/gcube/informationsystem/discovery/knowledge/UsageKnowledge.java
@@ -1,4 +1,4 @@
-package org.gcube.informationsystem.types.knowledge;
+package org.gcube.informationsystem.discovery.knowledge;
 
 import java.util.Collection;
 import java.util.LinkedHashMap;
diff --git a/src/main/java/org/gcube/informationsystem/types/knowledge/AddTypeToTreeAction.java b/src/main/java/org/gcube/informationsystem/types/knowledge/AddTypeToTreeAction.java
deleted file mode 100644
index d27716b..0000000
--- a/src/main/java/org/gcube/informationsystem/types/knowledge/AddTypeToTreeAction.java
+++ /dev/null
@@ -1,44 +0,0 @@
-/**
- * 
- */
-package org.gcube.informationsystem.types.knowledge;
-
-import org.gcube.informationsystem.base.reference.AccessType;
-import org.gcube.informationsystem.base.reference.Element;
-import org.gcube.informationsystem.discovery.DiscoveredElementAction;
-import org.gcube.informationsystem.tree.Tree;
-import org.gcube.informationsystem.types.TypeMapper;
-import org.gcube.informationsystem.types.reference.Type;
-import org.gcube.informationsystem.types.reference.entities.ResourceType;
-
-/**
- * @author Luca Frosini (ISTI - CNR)
- */
-public class AddTypeToTreeAction implements DiscoveredElementAction<Element> {
-
-	protected Tree<Type> tree;
-	
-	public AddTypeToTreeAction(Tree<Type> tree) {
-		this.tree = tree;
-	}
-	
-	@Override
-	public void analizeElement(Class<Element> e) throws Exception {
-		Type type = TypeMapper.createTypeDefinition(e);
-		tree.addNode(type);
-		createUsageKnowledge(type);
-	}
-	
-	
-	protected void createUsageKnowledge(Type type) {
-		if (type.getAccessType() != AccessType.RESOURCE) {
-			return;
-		}
-		ResourceType rt = (ResourceType) type;
-		UsageKnowledge fk = UsageKnowledge.getFacetKnowledge();
-		fk.addAll(rt.getFacets());
-		UsageKnowledge rk = UsageKnowledge.getResourceKnowledge();
-		rk.addAll(rt.getResources());
-	}
-
-}
diff --git a/src/main/java/org/gcube/informationsystem/types/knowledge/TypeInformation.java b/src/main/java/org/gcube/informationsystem/types/knowledge/TypeInformation.java
deleted file mode 100644
index d6d96d5..0000000
--- a/src/main/java/org/gcube/informationsystem/types/knowledge/TypeInformation.java
+++ /dev/null
@@ -1,27 +0,0 @@
-package org.gcube.informationsystem.types.knowledge;
-
-import java.util.HashSet;
-import java.util.Set;
-
-import org.gcube.informationsystem.tree.NodeInformation;
-import org.gcube.informationsystem.types.reference.Type;
-
-/**
- * @author Luca Frosini (ISTI - CNR)
- */
-public class TypeInformation implements NodeInformation<Type> {
-
-	@Override
-	public String getIdentifier(Type type) {
-		return type.getName();
-	}
-
-	@Override
-	public Set<String> getParentIdentifiers(Type root, Type type) {
-		if(getIdentifier(type).compareTo(getIdentifier(root))==0) {
-			return new HashSet<>();
-		}
-		return type.getSuperClasses();
-	}
-
-}