diff --git a/src/backend/concrete_environment.cc b/src/backend/concrete_environment.cc
index 6538821..a445db4 100644
--- a/src/backend/concrete_environment.cc
+++ b/src/backend/concrete_environment.cc
@@ -59,7 +59,7 @@ ConcreteEnvironment::ConcreteEnvironment(const ConcreteEnvironment & c) :
 
 
 
-const std::vector<Process *>
+const std::vector<Process*>&
 ConcreteEnvironment::get_processes() const
 {
   return _processes;
@@ -67,7 +67,7 @@ ConcreteEnvironment::get_processes() const
 
 
 
-std::vector<Process *>
+std::vector<Process*>&
 ConcreteEnvironment::get_processes()
 {
   return _processes;
@@ -75,7 +75,7 @@ ConcreteEnvironment::get_processes()
 
 
 
-const std::map<int, Resource *>
+const std::map<int, Resource*>&
 ConcreteEnvironment::get_resources() const
 {
   return _resources;
@@ -83,7 +83,7 @@ ConcreteEnvironment::get_resources() const
 
 
 
-std::map<int, Resource *>
+std::map<int, Resource*>&
 ConcreteEnvironment::get_resources()
 {
   return _resources;
@@ -91,7 +91,7 @@ ConcreteEnvironment::get_resources()
 
 
 
-const std::vector<Request *>
+const std::vector<Request*>
 ConcreteEnvironment::get_request_queue(Resource * resource) const
 {
   std::vector<Request *> request_queue;
@@ -102,18 +102,18 @@ ConcreteEnvironment::get_request_queue(Resource * resource) const
 
 
 
-const ReadyQueue *
+const ReadyQueue&
 ConcreteEnvironment::get_sorted_queue() const
 {
-  return &_sched_queue;
+  return _sched_queue;
 }
 
 
 
-ReadyQueue *
+ReadyQueue&
 ConcreteEnvironment::get_sorted_queue()
 {
-  return &_sched_queue;
+  return _sched_queue;
 }
 
 
diff --git a/src/backend/concrete_environment.hh b/src/backend/concrete_environment.hh
index 5aefb85..71aca26 100644
--- a/src/backend/concrete_environment.hh
+++ b/src/backend/concrete_environment.hh
@@ -82,7 +82,7 @@ namespace sgpem
     ///
     /// \return a constant set of snapshots of processes
 
-    virtual const std::vector<Process *>
+    virtual const std::vector<Process*>&
     get_processes() const;
 
 
@@ -92,7 +92,7 @@ namespace sgpem
     /// \return a set of snapshots of processes
     /// \see get_processes()
 
-    virtual std::vector<Process *>
+    virtual std::vector<Process*>&
     get_processes();
 
 
@@ -116,7 +116,7 @@ namespace sgpem
     /// \return a indexed constant set of snapshot of resources.
     /// \see DynamicSybrequest::get_resource()
 
-    virtual const std::map<int, Resource *>
+    virtual const std::map<int, Resource*>&
     get_resources() const;
 
 
@@ -126,7 +126,7 @@ namespace sgpem
     /// \return an indexed set of snapshots of resources
     /// \see get_resources()
 
-    virtual std::map<int, Resource *>
+    virtual std::map<int, Resource*>&
     get_resources();
 
 
@@ -143,7 +143,7 @@ namespace sgpem
     /// \param resource the resource the requests are for
     /// \return the current ready requests queue.
 
-    virtual const std::vector<Request *>
+    virtual const std::vector<Request*>
     get_request_queue(Resource * resource) const;
 
 
@@ -156,7 +156,7 @@ namespace sgpem
     ///
     /// \return the current ready queue (constant).
 
-    virtual const ReadyQueue *
+    virtual const ReadyQueue&
     get_sorted_queue() const;
 
 
@@ -166,7 +166,7 @@ namespace sgpem
     /// \return the current ready queue.
     /// \see get_sorted_queue()
 
-    virtual ReadyQueue *
+    virtual ReadyQueue&
     get_sorted_queue();
 
 
diff --git a/src/backend/environment.hh b/src/backend/environment.hh
index 9286803..ef64390 100644
--- a/src/backend/environment.hh
+++ b/src/backend/environment.hh
@@ -62,7 +62,7 @@ namespace sgpem
     ///
     /// \return a constant set of snapshots of processes
 
-    virtual std::vector<Process *> const
+    virtual const std::vector<Process*>&
     get_processes() const = 0;
 
 
@@ -80,7 +80,7 @@ namespace sgpem
     ///
     /// \return an indexed constant set of snapshot of resources.
 
-    virtual std::map<int, Resource *> const
+    virtual const std::map<int, Resource*>&
     get_resources() const = 0;
 
 
@@ -91,7 +91,7 @@ namespace sgpem
     /// \param resource the resource the requests are for
     /// \return the current ready requests queue (constant).
 
-    virtual std::vector<Resource *> const
+    virtual const std::vector<Request*>
     get_request_queue(const Resource * resource) const = 0;
 
 
@@ -102,7 +102,7 @@ namespace sgpem
     /// of the CPU.
     /// \return the current ready queue (constant).
 
-    virtual const ReadyQueue *
+    virtual const ReadyQueue&
     get_sorted_queue() const = 0;
 
 
@@ -110,8 +110,7 @@ namespace sgpem
     /// The standard virtual destructor.
 
     virtual
-    ~Environment();
-
+    ~Environment() = 0;
   };
 
 }