diff --git a/src/main/scala/com/normation/cfclerk/domain/TechniqueCategory.scala b/src/main/scala/com/normation/cfclerk/domain/TechniqueCategory.scala
index ed38385..e25ae12 100644
--- a/src/main/scala/com/normation/cfclerk/domain/TechniqueCategory.scala
+++ b/src/main/scala/com/normation/cfclerk/domain/TechniqueCategory.scala
@@ -170,23 +170,23 @@ sealed trait TechniqueCategory {
 }
 
 case class RootTechniqueCategory(
-  name : String,
-  description : String,
-  subCategoryIds: Set[SubTechniqueCategoryId] = Set(),
-  packageIds : SortedSet[TechniqueId] = SortedSet(),
-  isSystem : Boolean = false
+    name          : String
+  , description   : String
+  , subCategoryIds: Set[SubTechniqueCategoryId] = Set()
+  , packageIds    : SortedSet[TechniqueId] = SortedSet()
+  , isSystem      : Boolean = false
 ) extends TechniqueCategory with HashcodeCaching {
   type A = RootTechniqueCategoryId.type
   override lazy val id : A = RootTechniqueCategoryId
 }
 
 case class SubTechniqueCategory(
-  override val id : SubTechniqueCategoryId,
-  name : String,
-  description : String,
-  subCategoryIds: Set[SubTechniqueCategoryId] = Set(),
-  packageIds : SortedSet[TechniqueId] = SortedSet(),
-  isSystem : Boolean = false
+    override val id : SubTechniqueCategoryId
+  , name            : String
+  , description     : String
+  , subCategoryIds  : Set[SubTechniqueCategoryId] = Set()
+  , packageIds      : SortedSet[TechniqueId] = SortedSet()
+  , isSystem        : Boolean = false
 ) extends TechniqueCategory with HashcodeCaching {
   type A = SubTechniqueCategoryId
 }
diff --git a/src/main/scala/com/normation/cfclerk/services/TechniqueLibraryUpdateNotification.scala b/src/main/scala/com/normation/cfclerk/services/TechniqueLibraryUpdateNotification.scala
index 258d6e9..a5310c9 100644
--- a/src/main/scala/com/normation/cfclerk/services/TechniqueLibraryUpdateNotification.scala
+++ b/src/main/scala/com/normation/cfclerk/services/TechniqueLibraryUpdateNotification.scala
@@ -34,9 +34,37 @@
 
 package com.normation.cfclerk.services
 
-import com.normation.cfclerk.domain.TechniqueId
+import com.normation.cfclerk.domain.TechniqueName
+import com.normation.cfclerk.domain.TechniqueVersion
 import com.normation.eventlog.EventActor
 import com.normation.eventlog.ModificationId
+import com.normation.cfclerk.domain.TechniqueName
+
+
+sealed trait TechniqueVersionModType
+case object VersionDeleted extends TechniqueVersionModType
+case object VersionAdded extends TechniqueVersionModType
+case object VersionUpdated extends TechniqueVersionModType
+
+sealed trait TechniquesLibraryUpdateType {
+  val techniqueName: TechniqueName
+}
+
+/**
+ * All version of a technique were deleted, so the technique is
+ * full deleted
+ */
+case class TechniqueDeleted(techniqueName: TechniqueName, deletedVersion: Set[TechniqueVersion]) extends TechniquesLibraryUpdateType
+
+/**
+ * Some version of a technique were modified, either:
+ * - added,
+ * - deleted,
+ * - modified.
+ *
+ * One version can have only ONE state update.
+ */
+case class TechniqueUpdated(techniqueName: TechniqueName, diff: Map[TechniqueVersion, TechniqueVersionModType]) extends TechniquesLibraryUpdateType
 
 /**
  * A trait that allows its implementation to get notification
@@ -51,7 +79,13 @@ trait TechniquesLibraryUpdateNotification {
   /**
    * A name to identify that callback
    */
-  def name:String
+  def name: String
+
+  /**
+   * Order:
+   * higher value for order mean the callback will happen latter
+   */
+  def order: Int
 
   /**
    * That method will be called when techniques are updated.
@@ -60,6 +94,6 @@ trait TechniquesLibraryUpdateNotification {
    * Description is a log description to explain why techniques should be updated
    * (user action, commit, etc).
    */
-  def updatedTechniques(TechniqueIds:Seq[TechniqueId], modId: ModificationId, actor: EventActor, reason: Option[String]) : Unit
+  def updatedTechniques(techniqueIds: Map[TechniqueName, TechniquesLibraryUpdateType], modId: ModificationId, actor: EventActor, reason: Option[String]) : Unit
 
-}
\ No newline at end of file
+}
diff --git a/src/main/scala/com/normation/cfclerk/services/TechniqueReader.scala b/src/main/scala/com/normation/cfclerk/services/TechniqueReader.scala
index ca8ef0d..6be9657 100644
--- a/src/main/scala/com/normation/cfclerk/services/TechniqueReader.scala
+++ b/src/main/scala/com/normation/cfclerk/services/TechniqueReader.scala
@@ -48,7 +48,9 @@ case class TechniquesInfo(
   , techniques: Map[TechniqueName, SortedMap[TechniqueVersion, Technique]]
     //head of categories is the root category
   , subCategories: Map[SubTechniqueCategoryId, TechniqueCategory]
-) extends HashcodeCaching
+) extends HashcodeCaching {
+  val allCategories = Map[TechniqueCategoryId, TechniqueCategory]() ++ subCategories + (rootCategory.id -> rootCategory)
+}
 
 //a mutable version of TechniquesInfo, for internal use only !
 private[services] class InternalTechniquesInfo(
@@ -117,6 +119,6 @@ trait TechniqueReader {
    * If the sequence is empty, then nothing changed. Else, the list of Technique with
    * *any* change will be given
    */
-  def getModifiedTechniques : Seq[TechniqueId]
+  def getModifiedTechniques : Map[TechniqueName, TechniquesLibraryUpdateType]
 }
 
diff --git a/src/main/scala/com/normation/cfclerk/services/TechniqueRepository.scala b/src/main/scala/com/normation/cfclerk/services/TechniqueRepository.scala
index 35e4fce..82f87df 100644
--- a/src/main/scala/com/normation/cfclerk/services/TechniqueRepository.scala
+++ b/src/main/scala/com/normation/cfclerk/services/TechniqueRepository.scala
@@ -45,10 +45,6 @@ import scala.collection.SortedSet
  *
  *
  */
-/**
- * @author vincent
- *
- */
 trait TechniqueRepository {
 
   /**
@@ -70,6 +66,15 @@ trait TechniqueRepository {
 
   //  def packageDirectory : File
 
+
+  /*
+   * Return the full information about technique.
+   * That TechniquesInfo data structure is self-consistent by construction,
+   * so any category reference as a subcategory of an other is
+   * defined in the map, all techniques in categories is also accessible. etc.
+   */
+  def getTechniquesInfo(): TechniquesInfo
+
   /**
    * Return all the policies available
    */
diff --git a/src/main/scala/com/normation/cfclerk/services/UpdateTechniqueLibrary.scala b/src/main/scala/com/normation/cfclerk/services/UpdateTechniqueLibrary.scala
index 40d1bf2..712ab6b 100644
--- a/src/main/scala/com/normation/cfclerk/services/UpdateTechniqueLibrary.scala
+++ b/src/main/scala/com/normation/cfclerk/services/UpdateTechniqueLibrary.scala
@@ -38,6 +38,7 @@ import net.liftweb.common.Box
 import com.normation.cfclerk.domain.TechniqueId
 import com.normation.eventlog.EventActor
 import com.normation.eventlog.ModificationId
+import com.normation.cfclerk.domain.TechniqueName
 
 /**
  * A trait that allows to update the reference policy
@@ -49,11 +50,11 @@ trait UpdateTechniqueLibrary {
    * Update the lib, and return the list of
    * actually updated policy templates.
    */
-  def update(modId: ModificationId, actor:EventActor, reason: Option[String]) : Box[Seq[TechniqueId]]
+  def update(modId: ModificationId, actor:EventActor, reason: Option[String]) : Box[Map[TechniqueName, TechniquesLibraryUpdateType]]
 
   /**
    * Allows callbacks to be called on a Policy Template library update.
    */
   def registerCallback(callback:TechniquesLibraryUpdateNotification) : Unit
 
-}
\ No newline at end of file
+}
diff --git a/src/main/scala/com/normation/cfclerk/services/impl/FSTechniqueReader.scala b/src/main/scala/com/normation/cfclerk/services/impl/FSTechniqueReader.scala
index a8daf58..4fdfaf1 100644
--- a/src/main/scala/com/normation/cfclerk/services/impl/FSTechniqueReader.scala
+++ b/src/main/scala/com/normation/cfclerk/services/impl/FSTechniqueReader.scala
@@ -107,7 +107,7 @@ class FSTechniqueReader(
   }
 
   //we never know when to read again
-  override def getModifiedTechniques : Seq[TechniqueId] = Seq()
+  override def getModifiedTechniques : Map[TechniqueName, TechniquesLibraryUpdateType] = Map()
 
   /**
    * Read the policies
@@ -359,4 +359,4 @@ class FSTechniqueReader(
 
     doc
   }
-}
\ No newline at end of file
+}
diff --git a/src/main/scala/com/normation/cfclerk/services/impl/GitTechniqueReader.scala b/src/main/scala/com/normation/cfclerk/services/impl/GitTechniqueReader.scala
index aeab96e..f3d7ceb 100644
--- a/src/main/scala/com/normation/cfclerk/services/impl/GitTechniqueReader.scala
+++ b/src/main/scala/com/normation/cfclerk/services/impl/GitTechniqueReader.scala
@@ -71,6 +71,7 @@ import org.eclipse.jgit.diff.DiffEntry
 import scala.collection.JavaConversions._
 import org.eclipse.jgit.diff.DiffFormatter
 import org.eclipse.jgit.errors.MissingObjectException
+import org.eclipse.jgit.diff.DiffEntry.ChangeType
 
 /**
  *
@@ -185,9 +186,9 @@ class GitTechniqueReader(
 
   private[this] var nextTechniquesInfoCache : (ObjectId,TechniquesInfo) = (revisionProvider.currentRevTreeId, currentTechniquesInfoCache)
   //a non empty list IS the indicator of differences between current and next
-  private[this] var modifiedTechniquesCache : Seq[TechniqueId] = Seq()
+  private[this] var modifiedTechniquesCache : Map[TechniqueName, TechniquesLibraryUpdateType] = Map()
 
-  override def getModifiedTechniques : Seq[TechniqueId] = {
+  override def getModifiedTechniques : Map[TechniqueName, TechniquesLibraryUpdateType] = {
     val nextId = revisionProvider.getAvailableRevTreeId
     if(nextId == nextTechniquesInfoCache._1) modifiedTechniquesCache
     else reader.synchronized { //update next and calculate diffs
@@ -199,32 +200,78 @@ class GitTechniqueReader(
 
       val diffFmt = new DiffFormatter(null)
       diffFmt.setRepository(repo.db)
-      val diffPathEntries : Set[TechniquePath] =
+      val diffPathEntries : Set[(TechniquePath, ChangeType)] =
         diffFmt.scan(revisionProvider.currentRevTreeId,nextId).flatMap { diffEntry =>
-          Seq(toTechniquePath(diffEntry.getOldPath), toTechniquePath(diffEntry.getNewPath))
+          Seq( (toTechniquePath(diffEntry.getOldPath), diffEntry.getChangeType), (toTechniquePath(diffEntry.getNewPath), diffEntry.getChangeType))
         }.toSet
       diffFmt.release
 
-      val modifiedTechniquePath = scala.collection.mutable.Set[TechniquePath]()
       /*
        * now, group diff entries by TechniqueId to find which were updated
        * we take into account any modifications, as anything among a
        * delete, rename, copy, add, modify must be accepted and the matching
        * datetime saved.
        */
-      diffPathEntries.foreach { path =>
-        allKnownTechniquePaths.find { TechniquePath =>
-          path.path.startsWith(TechniquePath.path)
-        }.foreach { TechniquePath =>
-          modifiedTechniquePath += TechniquePath
-        } //else nothing
+      val modifiedTechnique : Set[(TechniqueId, ChangeType)] = diffPathEntries.flatMap { case (path, changeType) =>
+        allKnownTechniquePaths.find { techniquePath =>
+          path.path.startsWith(techniquePath.path)
+        }.map { techniquePath =>
+          val parts = techniquePath.path.split("/")
+          val id = TechniqueId(TechniqueName(parts(parts.size - 2)), TechniqueVersion(parts(parts.size - 1)))
+
+          (id, changeType)
+        }
       }
 
+      //now, build the actual modification by techniques:
+      val techniqueMods = modifiedTechnique.groupBy( _._1.name ).map { case (name, mods) =>
+        //deduplicate mods by ids:
+        val versionsMods: Map[TechniqueVersion, TechniqueVersionModType] = mods.groupBy( _._1.version).map { case(version, pairs) =>
+          val modTypes = pairs.map( _._2 ).toSet
+
+          //merge logic
+          //delete + add (+mod) => have to check if still present
+          //delete (+ mod) => delete
+          //add (+ mod) => add
+          //other: mod
+          if(modTypes.contains(ChangeType.DELETE)) {
+            if(modTypes.contains(ChangeType.ADD)) {
+              if(currentTechniquesInfoCache.techniquesCategory.isDefinedAt(TechniqueId(name, version))) {
+                //it was present before mod, so can't have been added first, so
+                //it was deleted then added (certainly a move), so it is actually mod
+                (version, VersionUpdated)
+              } else {
+                //it was not here, so was added then deleted, so it's a noop.
+                //not sure we want to trace that ? As a deletion perhaps ?
+                (version, VersionDeleted)
+              }
+            } else {
+              (version, VersionDeleted)
+            }
+          } else if(modTypes.contains(ChangeType.ADD)) {
+            //add
+            (version, VersionAdded)
+          } else {
+            //mod
+            (version, VersionUpdated)
+          }
+        }.toMap
+
+        //now, build the technique mod.
+        //distinguish the case where all mod are deletion AND they represent the whole set of known version
+        //from other case (just simple updates)
+
+        if(versionsMods.values.forall( _ == VersionDeleted)
+           && currentTechniquesInfoCache.techniques.get(name).map( _.size) == Some(versionsMods.size)
+        ) {
+          (name, TechniqueDeleted(name, versionsMods.keySet))
+        } else {
+          (name, TechniqueUpdated(name, versionsMods))
+        }
+      }.toMap
+
       //Ok, now rebuild Technique !
-      modifiedTechniquesCache = modifiedTechniquePath.map { s =>
-        val parts = s.path.split("/")
-        TechniqueId(TechniqueName(parts(parts.size - 2)), TechniqueVersion(parts(parts.size - 1)))
-      }.toSeq
+      modifiedTechniquesCache = techniqueMods
       nextTechniquesInfoCache = (nextId, nextTechniquesInfo)
       modifiedTechniquesCache
     }
@@ -362,7 +409,7 @@ class GitTechniqueReader(
       if(modifiedTechniquesCache.nonEmpty) {
         currentTechniquesInfoCache = nextTechniquesInfoCache._2
         revisionProvider.setCurrentRevTreeId(nextTechniquesInfoCache._1)
-        modifiedTechniquesCache = Seq()
+        modifiedTechniquesCache = Map()
       }
       currentTechniquesInfoCache
     }
diff --git a/src/main/scala/com/normation/cfclerk/services/impl/TechniqueRepositoryImpl.scala b/src/main/scala/com/normation/cfclerk/services/impl/TechniqueRepositoryImpl.scala
index b8aed33..ccda9db 100644
--- a/src/main/scala/com/normation/cfclerk/services/impl/TechniqueRepositoryImpl.scala
+++ b/src/main/scala/com/normation/cfclerk/services/impl/TechniqueRepositoryImpl.scala
@@ -56,7 +56,7 @@ class TechniqueRepositoryImpl(
   /**
    * Callback to call on PTLib update
    */
-  private[this] val callbacks = scala.collection.mutable.Buffer(refLibCallbacks:_*)
+  private[this] var callbacks = refLibCallbacks.sortBy( _.order )
 
 
   /*
@@ -86,19 +86,27 @@ class TechniqueRepositoryImpl(
 
 
   /**
-   * Register a new callback
+   * Register a new callback with a order.
+   * Sort by order after each registration
    */
   override def registerCallback(callback:TechniquesLibraryUpdateNotification) : Unit = {
-    callbacks.append(callback)
+    callbacks = (callbacks :+ callback).sortBy( _.order )
   }
 
-  override def update(modId: ModificationId, actor:EventActor, reason: Option[String]) : Box[Seq[TechniqueId]] = {
+  override def update(modId: ModificationId, actor:EventActor, reason: Option[String]) : Box[Map[TechniqueName, TechniquesLibraryUpdateType]] = {
     try {
       val modifiedPackages = techniqueReader.getModifiedTechniques
       if (modifiedPackages.nonEmpty || /* first time init */ null == techniqueInfosCache) {
         logger.info("Reloading technique library, " + {
           if (modifiedPackages.isEmpty) "no modified techniques found"
-          else "found modified technique(s): " + modifiedPackages.mkString(", ")
+          else {
+            val details = modifiedPackages.values.map {
+              case TechniqueDeleted(name, versions) => s"['${name}': deleted (${versions.mkString(", ")})]"
+              case TechniqueUpdated(name, mods)     => s"['${name}': updated (${mods.map(x => s"${x._1}: ${x._2}").mkString(", ")})]"
+            }
+
+            "found modified technique(s): " + details.mkString(", ")
+          }
         })
         techniqueInfosCache = techniqueReader.readTechniques
 
@@ -142,6 +150,8 @@ class TechniqueRepositoryImpl(
     }).toMap
   }
 
+  override def getTechniquesInfo() = techniqueInfosCache
+
   override def getTechniqueVersions(name: TechniqueName): SortedSet[TechniqueVersion] = {
     SortedSet[TechniqueVersion]() ++ techniqueInfosCache.techniques.get(name).toSeq.flatMap(_.keySet)
   }
@@ -174,7 +184,11 @@ class TechniqueRepositoryImpl(
   }
 
   override def getLastTechniqueByName(policyName: TechniqueName): Option[Technique] = {
-    techniqueInfosCache.techniques.get(policyName).map { versions => versions.last._2 }
+    for {
+      versions <- techniqueInfosCache.techniques.get(policyName)
+    } yield {
+      versions.last._2
+    }
   }
 
   //////////////////////////////////// categories /////////////////////////////
diff --git a/src/test/scala/com/normation/cfclerk/services/DummyTechniqueReader.scala b/src/test/scala/com/normation/cfclerk/services/DummyTechniqueReader.scala
index fcd008d..c269ed8 100644
--- a/src/test/scala/com/normation/cfclerk/services/DummyTechniqueReader.scala
+++ b/src/test/scala/com/normation/cfclerk/services/DummyTechniqueReader.scala
@@ -75,6 +75,6 @@ class DummyTechniqueReader(policies:Seq[Technique]=Seq(Technique(TechniqueId(Tec
   def getMetadataContent[T](techniqueId: TechniqueId)(useIt : Option[InputStream] => T) : T = useIt(None)
   def getReportingDetailsContent[T](techniqueId: TechniqueId)(useIt : Option[InputStream] => T) : T = useIt(None)
   def getTemplateContent[T](templateName: Cf3PromisesFileTemplateId)(useIt : Option[InputStream] => T) : T = useIt(None)
-  def getModifiedTechniques : Seq[TechniqueId] = Seq()
+  def getModifiedTechniques : Map[TechniqueName, TechniquesLibraryUpdateType] = Map()
 
 }
diff --git a/src/test/scala/com/normation/cfclerk/services/DummyTechniqueRepository.scala b/src/test/scala/com/normation/cfclerk/services/DummyTechniqueRepository.scala
index 986e7cf..2ec1a3b 100644
--- a/src/test/scala/com/normation/cfclerk/services/DummyTechniqueRepository.scala
+++ b/src/test/scala/com/normation/cfclerk/services/DummyTechniqueRepository.scala
@@ -87,21 +87,8 @@ class DummyTechniqueRepository(policies: Seq[Technique] = Seq()) extends Techniq
 
   def getByName(policyName: TechniqueName) = ???
 
-//  def getVariables(policyName: TechniqueId, includeSystemVar: Boolean = false): Seq[VariableSpec] =
-//    policyName.name.value match {
-//      case "policy1" =>
-//        List(InputVariableSpec("$variable1", "a variable1"))
-//      case "policy2" =>
-//        val variable = InputVariableSpec("$variable2", "a variable2", multivalued = true)
-//        List(variable, InputVariableSpec("$variable22", "a variable22"))
-//      case "policy3" =>
-//        List(InputVariableSpec("$variable3", "a variable3"))
-//      case "policy4" =>
-//        List(InputVariableSpec("$variable4", "an variable4"))
-//      case "foo" =>
-//        List(InputVariableSpec("$bar", "bar"))
-//    }
-//
+  def getTechniquesInfo = ???
+
   override def getTechniqueVersions(name:TechniqueName) : SortedSet[TechniqueVersion] = SortedSet.empty[TechniqueVersion]
 
   def manageDependencies(chosenTemplate: Seq[Cf3PromisesFileTemplateId] , includeExternalDependencies : Boolean = true) : Seq[Cf3PromisesFileTemplateId] = {
@@ -114,4 +101,4 @@ class DummyTechniqueRepository(policies: Seq[Technique] = Seq()) extends Techniq
   def getParents_TechniqueCategory(id: TechniqueCategoryId): Box[List[TechniqueCategory]] = null
   def getParentTechniqueCategory_forTechnique(id: TechniqueId): Box[TechniqueCategory] = null
 
-}
\ No newline at end of file
+}