diff --git a/src/doxygen.dox b/src/doxygen.dox
index e794bd331..4a7746672 100644
--- a/src/doxygen.dox
+++ b/src/doxygen.dox
@@ -72,6 +72,10 @@ with the *ASCIIDOC* tool and published at the [Lumiera website](http://Lumiera.o
     @ingroup steam
 */
 
+/** @defgroup fixture Fixture and low-level-Model
+    @ingroup steam
+*/
+
 /** @defgroup player Playback and Render Control
     @ingroup steam
 */
diff --git a/src/steam/common.hpp b/src/steam/common.hpp
index cd474c660..62bb5ba28 100644
--- a/src/steam/common.hpp
+++ b/src/steam/common.hpp
@@ -126,6 +126,19 @@ namespace steam {
   
   
   }//(End)namespace mobject
+  
+  
+  /**
+   * Fixture and low-level-Model.
+   * The shared data structure used as render nodes network.
+   * It is created or updated by the [Builder](\ref session::builder)
+   * after any relevant change of \ref Session contents, while used
+   * by the engine as work data structure for the render jobs.
+   */
+  namespace fixture {
+    
+  }
+  
 } //(End)namespace steam
 
 #endif /*STEAM_COMMON_H*/
diff --git a/src/steam/mobject/session/fixture.cpp b/src/steam/fixture/fixture.cpp
similarity index 93%
rename from src/steam/mobject/session/fixture.cpp
rename to src/steam/fixture/fixture.cpp
index fb1578308..78373f297 100644
--- a/src/steam/mobject/session/fixture.cpp
+++ b/src/steam/fixture/fixture.cpp
@@ -28,12 +28,11 @@
  */
 
 
-#include "steam/mobject/session/fixture.hpp"
+#include "steam/fixture/fixture.hpp"
 #include "include/logging.h"
 
 namespace steam {
-namespace mobject {
-namespace session {
+namespace fixture {
   
   
   
@@ -66,4 +65,4 @@ namespace session {
   
   
   
-}}} // namespace steam::mobject::session
+}} // namespace steam::fixture
diff --git a/src/steam/mobject/session/fixture.hpp b/src/steam/fixture/fixture.hpp
similarity index 89%
rename from src/steam/mobject/session/fixture.hpp
rename to src/steam/fixture/fixture.hpp
index dc579eabf..28a931c51 100644
--- a/src/steam/mobject/session/fixture.hpp
+++ b/src/steam/fixture/fixture.hpp
@@ -35,15 +35,17 @@
  ** of a more recent builder run. Ongoing render processes are also tracked per segment,
  ** which allows the individual calculation steps just to assume the data is "there".
  ** 
+ ** @ingroup fixture
+ ** 
  ** @todo WIP implementation of session core from 2010
  ** @todo as of 2016, this effort is considered stalled but basically valid
  */
 
 
-#ifndef MOBJECT_SESSION_FIXTURE_H
-#define MOBJECT_SESSION_FIXTURE_H
+#ifndef STEAM_FIXTURE_FIXTURE_H
+#define STEAM_FIXTURE_FIXTURE_H
 
-#include "steam/mobject/session/segmentation.hpp"
+#include "steam/fixture/segmentation.hpp"
 #include "steam/mobject/session/fork.hpp"
 #include "steam/mobject/explicitplacement.hpp"
 #include "steam/mobject/session/auto.hpp"
@@ -60,12 +62,14 @@ using std::unique_ptr;
 
 
 namespace steam {
-namespace mobject {
-namespace session {
+namespace fixture {
   
+  using mobject::session::Auto;
+  using mobject::ExplicitPlacement;
   
   
   /**
+   * @ingroup fixture
    * @todo 1/2012 Just a Placeholder. The real thing is not yet implemented.
    * @see http://lumiera.org/wiki/renderengine.html#Fixture
    */
@@ -86,7 +90,7 @@ namespace session {
       bool isValid()  const;
       
     private:
-      virtual bool validate() 
+      virtual bool validate()
         {
           TODO ("how to validate a Fixture?");
           return false;
@@ -94,11 +98,9 @@ namespace session {
       
     };
   
-  
-  
-  typedef shared_ptr<Fixture> PFix;
+  using PFixture = shared_ptr<Fixture>;
   
   
   
-}}} // namespace steam::mobject::session
-#endif
+}} // namespace steam::fixture
+#endif /*STEAM_FIXTURE_FIXTURE_H*/
diff --git a/src/steam/mobject/session/segment.cpp b/src/steam/fixture/segment.cpp
similarity index 90%
rename from src/steam/mobject/session/segment.cpp
rename to src/steam/fixture/segment.cpp
index b977c41c3..b852145dc 100644
--- a/src/steam/mobject/session/segment.cpp
+++ b/src/steam/fixture/segment.cpp
@@ -26,17 +26,16 @@
  ** @todo 2016 likely to stay, but expect some extensive rework
  */
 
-#include "steam/mobject/session/segment.hpp"
+#include "steam/fixture/segment.hpp"
 #include "steam/mobject/explicitplacement.hpp"
 
 
 
 namespace steam {
-namespace mobject {
-namespace session {
+namespace fixture {
   
   /** */
   
   
   
-}}} // namespace steam::mobject::session
+}} // namespace steam::fixture
diff --git a/src/steam/mobject/session/segment.hpp b/src/steam/fixture/segment.hpp
similarity index 91%
rename from src/steam/mobject/session/segment.hpp
rename to src/steam/fixture/segment.hpp
index b288da305..a6dd17cb3 100644
--- a/src/steam/mobject/session/segment.hpp
+++ b/src/steam/fixture/segment.hpp
@@ -28,8 +28,8 @@
  */
 
 
-#ifndef MOBJECT_SESSION_SEGMENT_H
-#define MOBJECT_SESSION_SEGMENT_H
+#ifndef STEAM_FIXTURE_SEGMENT_H
+#define STEAM_FIXTURE_SEGMENT_H
 
 #include <list>
 
@@ -40,9 +40,9 @@
 using std::list;
 
 namespace steam {
-namespace mobject {
-namespace session {
+namespace fixture {
   
+  using mobject::ExplicitPlacement;
   
   /**
    * For the purpose of building and rendering, the fixture (for each timeline)
@@ -50,6 +50,7 @@ namespace session {
    * For each segment there is a RenderGraph (unit of the render engine) which
    * is able to render all ExitNodes for this segment.
    * 
+   * @ingroup fixture
    * @todo 1/2012 Just a Placeholder. The real thing is not yet implemented.
    * @see http://lumiera.org/wiki/renderengine.html#Fixture
    */
@@ -71,5 +72,5 @@ namespace session {
   
   
   
-}}} // namespace steam::mobject::session
-#endif
+}} // namespace steam::fixture
+#endif /*STEAM_FIXTURE_SEGMENT_H*/
diff --git a/src/steam/mobject/session/segmentation.cpp b/src/steam/fixture/segmentation.cpp
similarity index 88%
rename from src/steam/mobject/session/segmentation.cpp
rename to src/steam/fixture/segmentation.cpp
index 9f5fd0608..1258e0674 100644
--- a/src/steam/mobject/session/segmentation.cpp
+++ b/src/steam/fixture/segmentation.cpp
@@ -1,5 +1,5 @@
 /*
-  Segementation  -  Partitioning of a timeline for organising the render graph.
+  Segmentation  -  Partitioning of a timeline for organising the render graph.
 
   Copyright (C)         Lumiera.org
     2008,               Hermann Vosseler <Ichthyostega@web.de>
@@ -27,14 +27,13 @@
  */
 
 #include "lib/error.hpp"
-#include "steam/mobject/session/segmentation.hpp"
-#include "steam/mobject/builder/fixture-change-detector.hpp"
+#include "steam/fixture/segmentation.hpp"
+//#include "steam/mobject/builder/fixture-change-detector.hpp"  ///////////TODO
 
 
 
 namespace steam {
-namespace mobject {
-namespace session {
+namespace fixture {
   
   namespace error = lumiera::error;
   
@@ -79,4 +78,4 @@ namespace session {
   
   
   
-}}} // namespace steam::mobject::session
+}} // namespace steam::fixture
diff --git a/src/steam/mobject/session/segmentation.hpp b/src/steam/fixture/segmentation.hpp
similarity index 93%
rename from src/steam/mobject/session/segmentation.hpp
rename to src/steam/fixture/segmentation.hpp
index 32bcf0e71..fb6a4d087 100644
--- a/src/steam/mobject/session/segmentation.hpp
+++ b/src/steam/fixture/segmentation.hpp
@@ -43,11 +43,11 @@
  */
 
 
-#ifndef MOBJECT_SESSION_SEGMENTATION_H
-#define MOBJECT_SESSION_SEGMENTATION_H
+#ifndef STEAM_FIXTURE_SEGMENTATION_H
+#define STEAM_FIXTURE_SEGMENTATION_H
 
 
-#include "steam/mobject/session/segment.hpp"
+#include "steam/fixture/segment.hpp"
 
 #include <list>
 
@@ -55,8 +55,7 @@ using std::list;
 
 
 namespace steam {
-namespace mobject {
-namespace session {
+namespace fixture {
   
   
   /**
@@ -65,6 +64,7 @@ namespace session {
    * The Segmentation defines and maintains this partitioning. Furthermore,
    * it is the general entry point for accessing the correct part of the engine
    * responsible for a given timeline time point.
+   * @ingroup fixture
    * @see SegmentationTool actually calculating the Segmentation
    * 
    * @todo 1/2012 Just a Placeholder. The real thing is not yet implemented.
@@ -84,5 +84,5 @@ namespace session {
   
   
   
-}}} // namespace steam::mobject::session
-#endif
+}} // namespace steam::fixture
+#endif /*STEAM_FIXTURE_SEGMENTATION_H*/
diff --git a/src/steam/mobject/builder/segmentation-tool.cpp b/src/steam/mobject/builder/segmentation-tool.cpp
index 11840742d..10a030c36 100644
--- a/src/steam/mobject/builder/segmentation-tool.cpp
+++ b/src/steam/mobject/builder/segmentation-tool.cpp
@@ -37,7 +37,7 @@ namespace builder {
   using mobject::Buildable;
   using session::Clip;
   using session::Effect;
-  using session::Fixture;
+  using fixture::Fixture;
   
                                       /////////////////////////////////TICKET #414
   
diff --git a/src/steam/mobject/builder/segmentation-tool.hpp b/src/steam/mobject/builder/segmentation-tool.hpp
index fd70efa17..28d176e41 100644
--- a/src/steam/mobject/builder/segmentation-tool.hpp
+++ b/src/steam/mobject/builder/segmentation-tool.hpp
@@ -37,8 +37,8 @@
 
 #include "steam/mobject/builder/applicable-builder-target-types.hpp"
 
-#include "steam/mobject/session/segmentation.hpp"
-#include "steam/mobject/session/fixture.hpp"   //////TODO really on the header??
+#include "steam/fixture/segmentation.hpp"
+#include "steam/fixture/fixture.hpp"   //////TODO really on the header??
 
 
 #include <list>
@@ -63,7 +63,7 @@ namespace builder {
     {
       
     public:
-      SegmentationTool (session::Fixture &) ;
+      SegmentationTool (fixture::Fixture &) ;
       
       void treat (mobject::session::Clip& clip) ;
       void treat (mobject::session::Effect& effect) ;
@@ -75,7 +75,7 @@ namespace builder {
       bool empty()  const;
       
     private:
-      typedef mobject::session::Segment Segment;
+      using Segment = fixture::Segment;
       
       /** Partitioning of the Timeline to be created by this tool. */
       //session::Segmentation& segments_;
diff --git a/src/steam/mobject/builder/toolfactory.cpp b/src/steam/mobject/builder/toolfactory.cpp
index 2f54cd953..b1b532dca 100644
--- a/src/steam/mobject/builder/toolfactory.cpp
+++ b/src/steam/mobject/builder/toolfactory.cpp
@@ -43,21 +43,21 @@ namespace builder {
   struct BuildProcessState
     {
       
-      session::Fixture & fixedTimeline_;
+      fixture::Fixture & fixedTimeline_;
       unique_ptr<engine::RenderGraph> procSegment_;
       
       unique_ptr<SegmentationTool> segmentation_;
       unique_ptr<NodeCreatorTool> fabrication_;
       
       
-      BuildProcessState (session::Fixture& theTimeline)
+      BuildProcessState (fixture::Fixture& theTimeline)
         : fixedTimeline_(theTimeline),
           procSegment_(new engine::RenderGraph())
         { }
       
     };
   
-  ToolFactory::ToolFactory (session::Fixture& theFixture)
+  ToolFactory::ToolFactory (fixture::Fixture& theFixture)
     : state_(new BuildProcessState (theFixture))
   {
     ENSURE (state_->fixedTimeline_.isValid());
diff --git a/src/steam/mobject/builder/toolfactory.hpp b/src/steam/mobject/builder/toolfactory.hpp
index e86778549..ddab9e901 100644
--- a/src/steam/mobject/builder/toolfactory.hpp
+++ b/src/steam/mobject/builder/toolfactory.hpp
@@ -33,7 +33,7 @@
 #ifndef MOBJECT_BUILDER_TOOLFACTORY_H
 #define MOBJECT_BUILDER_TOOLFACTORY_H
 
-#include "steam/mobject/session/fixture.hpp"
+#include "steam/fixture/fixture.hpp"
 #include "steam/mobject/builder/segmentation-tool.hpp"
 #include "steam/mobject/builder/nodecreatortool.hpp"
 #include "steam/mobject/builder/mould.hpp"
@@ -63,7 +63,7 @@ namespace builder {
     public:
       /** prepare a builder tool kit for dealing with the given Fixture,
        *  which is a snapshot of some timeline made explicit. */
-      ToolFactory (session::Fixture&);
+      ToolFactory (fixture::Fixture&);
       
       /** prepare a tool for properly segmenting the Fixture */
       SegmentationTool &  configureSegmentation ();
diff --git a/src/steam/mobject/builderfacade.cpp b/src/steam/mobject/builderfacade.cpp
index 2b83410b2..593e4b7df 100644
--- a/src/steam/mobject/builderfacade.cpp
+++ b/src/steam/mobject/builderfacade.cpp
@@ -28,7 +28,7 @@
 
 #include "steam/mobject/builder/common.hpp"
 #include "steam/mobject/builderfacade.hpp"
-#include "steam/mobject/session/fixture.hpp"
+#include "steam/fixture/fixture.hpp"
 
 namespace steam {
 namespace mobject {
diff --git a/src/steam/mobject/explicitplacement.hpp b/src/steam/mobject/explicitplacement.hpp
index 800da48e2..608bc3bfb 100644
--- a/src/steam/mobject/explicitplacement.hpp
+++ b/src/steam/mobject/explicitplacement.hpp
@@ -57,6 +57,7 @@ namespace mobject {
    * contains only ExplicitPlacement objects and is processed
    * by the Builder to create the render engine  node network.
    *
+   * @ingroup fixture
    * @see Placement#resolve factory method for deriving an ExplicitPlacement 
    */
   class ExplicitPlacement : public Placement<MObject>
diff --git a/src/steam/mobject/session.hpp b/src/steam/mobject/session.hpp
index 8ef74aa5b..0f2bb6564 100644
--- a/src/steam/mobject/session.hpp
+++ b/src/steam/mobject/session.hpp
@@ -67,14 +67,16 @@ namespace asset {
   class Timeline;    typedef lib::P<Timeline> PTimeline;
   class Sequence;    typedef lib::P<Sequence> PSequence;
 }
+namespace fixture {
+    class Fixture;
+    using PFixture = std::shared_ptr<Fixture>;
+}
 
 namespace mobject {
   
   namespace session { 
     class SessManager;
     class ElementQuery;
-    class Fixture;
-    typedef std::shared_ptr<Fixture> PFix;
   }
   
   typedef session::SessManager& PSess;  ///< acts as a "PImpl" smart ptr
@@ -137,7 +139,7 @@ namespace mobject {
       
       virtual MObjectRef getRoot()                     = 0;
       
-      virtual session::PFix& getFixture ()             = 0;
+      virtual fixture::PFixture& getFixture ()         = 0;
       virtual void rebuildFixture ()                   = 0;
       
     };
diff --git a/src/steam/mobject/session/session-impl.cpp b/src/steam/mobject/session/session-impl.cpp
index 431b8aa2d..4242c1710 100644
--- a/src/steam/mobject/session/session-impl.cpp
+++ b/src/steam/mobject/session/session-impl.cpp
@@ -54,7 +54,7 @@ namespace session {
              , timelineRegistry_
              , sequenceRegistry_ )
     , contents_( MObject::create (defaultsManager_))
-    , fixture_(new Fixture)
+    , fixture_(new fixture::Fixture)
     {
       INFO (session, "new Session created.");
     }
@@ -141,7 +141,7 @@ namespace session {
 
   
   
-  PFix&
+  PFixture&
   SessionImpl::getFixture ()
   {
     return fixture_;
diff --git a/src/steam/mobject/session/session-impl.hpp b/src/steam/mobject/session/session-impl.hpp
index 4528a2856..b90175e82 100644
--- a/src/steam/mobject/session/session-impl.hpp
+++ b/src/steam/mobject/session/session-impl.hpp
@@ -47,7 +47,7 @@
 #define STEAM_MOBJECT_SESSION_SESSIONIMPL_H
 
 #include "steam/mobject/session.hpp"
-#include "steam/mobject/session/fixture.hpp"
+#include "steam/fixture/fixture.hpp"
 #include "steam/mobject/session/placement-index.hpp"
 #include "steam/mobject/session/session-services.hpp"
 #include "steam/mobject/session/session-interface-modules.hpp"
@@ -67,6 +67,7 @@ namespace steam {
 namespace mobject {
 namespace session {
   
+  using fixture::PFixture;
   
   
   /**
@@ -78,7 +79,7 @@ namespace session {
     {
       PlacementIndex contents_;
       
-      PFix fixture_;
+      PFixture fixture_;
       
       
       
@@ -88,10 +89,10 @@ namespace session {
       virtual MObjectRef attach (PMO const& placement)  override;
       virtual bool       detach (PMO const& placement)  override;
       
-      virtual MObjectRef getRoot()  override;
+      virtual MObjectRef getRoot()   override;
 
-      virtual PFix& getFixture()    override;
-      virtual void rebuildFixture() override;
+      virtual PFixture& getFixture() override;
+      virtual void rebuildFixture()  override;
       
     protected: /* == management API === */
       SessionImpl ();
diff --git a/tests/core/steam/engine/mock-dispatcher.hpp b/tests/core/steam/engine/mock-dispatcher.hpp
index e71c058ec..f36588e41 100644
--- a/tests/core/steam/engine/mock-dispatcher.hpp
+++ b/tests/core/steam/engine/mock-dispatcher.hpp
@@ -31,7 +31,7 @@
 
 ////#include "steam/engine/procnode.hpp"
 //#include "steam/play/dummy-play-connection.hpp"
-#include "steam/mobject/session/segmentation.hpp"
+#include "steam/fixture/segmentation.hpp"
 #include "steam/mobject/model-port.hpp"
 #include "steam/engine/dispatcher.hpp"
 #include "steam/engine/job-ticket.hpp"
@@ -82,7 +82,7 @@ namespace test   {
   using std::make_tuple;
   using std::deque;
   ///////////////////////////////////////////////////////////////////////////////////////////////////////////TICKET #1294 : organisation of namespaces / includes??
-  using steam::mobject::session::Segmentation;
+  using fixture::Segmentation;
   
   namespace { // used internally
     
diff --git a/tests/core/steam/mobject/session/deletecliptest.cpp b/tests/core/steam/mobject/session/deletecliptest.cpp
index a3e126a24..f84b6af8f 100644
--- a/tests/core/steam/mobject/session/deletecliptest.cpp
+++ b/tests/core/steam/mobject/session/deletecliptest.cpp
@@ -35,15 +35,15 @@
 
 
 //using std::string;
+using std::dynamic_pointer_cast;     //////////////////// TODO only temp
 
 using proc_interface::AssetManager;
 using proc_interface::PAsset;
 using proc_interface::IDA;
 
-using std::dynamic_pointer_cast;        /// TODO only temp
 
 
-namespace steam    {
+namespace steam   {
 namespace mobject {
 namespace session {
 namespace test    {
diff --git a/tests/core/steam/mobject/session/session-modify-parts-test.cpp b/tests/core/steam/mobject/session/session-modify-parts-test.cpp
index ba71723cc..b32ceea58 100644
--- a/tests/core/steam/mobject/session/session-modify-parts-test.cpp
+++ b/tests/core/steam/mobject/session/session-modify-parts-test.cpp
@@ -27,7 +27,7 @@
 
 #include "lib/test/run.hpp"
 #include "steam/mobject/session.hpp"
-#include "steam/mobject/session/fixture.hpp"             // TODO only temporarily needed
+#include "steam/fixture/fixture.hpp"             // TODO only temporarily needed
 //#include "steam/assetmanager.hpp"          //////??
 //#include "steam/asset/timeline.hpp"
 #include "steam/asset/sequence.hpp"
diff --git a/tests/core/steam/mobject/session/session-structure-test.cpp b/tests/core/steam/mobject/session/session-structure-test.cpp
index 3f0f636f9..8c8c83f8b 100644
--- a/tests/core/steam/mobject/session/session-structure-test.cpp
+++ b/tests/core/steam/mobject/session/session-structure-test.cpp
@@ -27,7 +27,7 @@
 
 #include "lib/test/run.hpp"
 #include "steam/mobject/session.hpp"
-#include "steam/mobject/session/fixture.hpp"             // TODO only temporarily needed
+#include "steam/fixture/fixture.hpp"             // TODO only temporarily needed
 #include "steam/assetmanager.hpp"          //////??
 #include "steam/asset/timeline.hpp"
 #include "steam/asset/sequence.hpp"