diff --git a/Makefile.am b/Makefile.am
index a8ef0cd..9d3bf3b 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -161,6 +161,7 @@ src_backend_libbackend_la_SOURCES = \
 		src/backend/global_preferences.cc \
 		src/backend/history.cc \
 		src/backend/history_observer.cc \
+		src/backend/holt_graph.cc \
 		src/backend/invalid_plugin_exception.cc \
 		src/backend/key_file.cc \
 		src/backend/module.cc \
@@ -198,6 +199,7 @@ pkginclude_HEADERS += \
 		src/backend/global_preferences.hh \
 		src/backend/history.hh \
 		src/backend/history_observer.hh \
+		src/backend/holt_graph.hh \
 		src/backend/invalid_plugin_exception.hh \
 		src/backend/key_file.hh \
 		src/backend/module.hh \
diff --git a/src/backend/holt_graph.cc b/src/backend/holt_graph.cc
new file mode 100644
index 0000000..6e9b9f3
--- /dev/null
+++ b/src/backend/holt_graph.cc
@@ -0,0 +1,88 @@
+// src/backend/holt_graph.cc - Copyright 2005, 2006, University
+//               of Padova, dept. of Pure and Applied
+//               Mathematics
+//
+// This file is part of SGPEMv2.
+//
+// This is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// SGPEMv2 is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with SGPEMv2; if not, write to the Free Software
+// Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+
+#include "holt_graph.hh"
+
+#include "history.hh"
+#include "process.hh"
+#include "thread.hh"
+
+using namespace sgpem;
+using namespace std;
+
+void 
+HoltGraph::update(const History& changed_history)
+{
+  const Environment& env = changed_history.get_last_environment();
+  const Environment::Processes& processes = env.get_processes();
+
+  _resources.clear();
+  _active_threads.clear();
+  _active_requests.clear();
+  
+  for(unsigned int pi = 0; pi < processes.size(); ++pi)
+  {
+    vector<Thread*> threads = processes[pi]->get_threads();
+
+    for(unsigned int ti = 0; ti < threads.size(); ++ti)
+    {
+      vector<Request*> requests = threads[ti]->get_requests();
+
+      for(unsigned int ri = 0; ri < requests.size(); ++ri)
+      {
+	Request& r = *requests[ri];
+
+	if(r.get_state() == Request::state_allocated)
+	{
+	  _active_requests.push_back(&r);
+	  _active_threads.insert(&r.get_thread());
+
+	  vector<SubRequest*> subrequests = r.get_subrequests();
+
+	  for(unsigned int sri = 0; sri < subrequests.size(); ++sri)
+	  {
+	    Environment::resource_key_t key = subrequests[sri]->get_resource_key();
+
+	    _resources.insert(env.get_resources().find(key)->second);
+	  }
+	}
+      }
+    }
+  }
+}
+
+HoltGraph::Resources
+HoltGraph::get_resources() const
+{
+  return Resources(_resources.begin(), _resources.end());
+}
+
+HoltGraph::Threads
+HoltGraph::get_active_threads() const
+{
+  return Threads(_active_threads.begin(), _active_threads.end());
+}
+
+HoltGraph::Requests
+HoltGraph::get_active_requests() const
+{
+  return _active_requests;
+}
+
diff --git a/src/backend/holt_graph.hh b/src/backend/holt_graph.hh
new file mode 100644
index 0000000..ce934ec
--- /dev/null
+++ b/src/backend/holt_graph.hh
@@ -0,0 +1,64 @@
+// src/backend/holt_graph.hh - Copyright 2005, 2006, University
+//               of Padova, dept. of Pure and Applied
+//               Mathematics
+//
+// This file is part of SGPEMv2.
+//
+// This is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 2 of the License, or
+// (at your option) any later version.
+//
+// SGPEMv2 is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with SGPEMv2; if not, write to the Free Software
+// Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+
+#ifndef HOLT_GRAPH_HH
+#define HOLT_GRAPH_HH 1
+
+namespace sgpem
+{
+  class Resource;
+  class Thread;
+  class Request;
+}
+
+#include "history_observer.hh"
+
+#include <set>
+#include <vector>
+
+namespace sgpem
+{
+  class HoltGraph;
+
+  class SG_DLLEXPORT HoltGraph : public HistoryObserver
+  {
+  public:
+    typedef std::vector<const Resource*> Resources;
+    typedef std::vector<const Thread*> Threads;
+    typedef std::vector<const Request*> Requests;
+    
+    HoltGraph();
+    
+    virtual void update(const History& changed_history);
+
+    Resources get_resources() const;
+    Threads get_active_threads() const;
+    Requests get_active_requests() const;
+
+  private:
+    std::set<const Resource*> _resources;
+    std::set<const Thread*> _active_threads;
+    Requests _active_requests;
+  }; // class HistoryObserver
+
+}//~ namespace sgpem
+
+#endif //HOLT_GRAPH_HH
+