diff --git a/include/XPath/impl/xpath_expression.hpp b/include/XPath/impl/xpath_expression.hpp
index 897dfe9c..389ed03f 100644
--- a/include/XPath/impl/xpath_expression.hpp
+++ b/include/XPath/impl/xpath_expression.hpp
@@ -48,30 +48,58 @@ public:
 
   XPathValue<string_type, string_adaptor> evaluate(const DOM::Node<string_type, string_adaptor>& context) const
   {
-    ExecutionContext<string_type, string_adaptor> executionContext;
-    return evaluate(context, executionContext);
+    return evaluate(context, StaticExecutionContext());
   } // evaluate
+  virtual bool evaluateAsBool(const DOM::Node<string_type, string_adaptor>& context) const 
+  { 
+    return evaluateAsBool(context, StaticExecutionContext()); 
+  }
+  virtual double evaluateAsNumber(const DOM::Node<string_type, string_adaptor>& context) const 
+  { 
+    return evaluateAsNumber(context, StaticExecutionContext()); 
+  }
+  virtual string_type evaluateAsString(const DOM::Node<string_type, string_adaptor>& context) const 
+  { 
+    return evaluateAsString(context, StaticExecutionContext()); 
+  }
+  virtual NodeSet<string_type, string_adaptor> evaluateAsNodeSet(const DOM::Node<string_type, string_adaptor>& context) const 
+  { 
+    return evaluateAsNodeSet(context, StaticExecutionContext()); 
+  }
 
-  virtual bool evaluateAsBool(const DOM::Node<string_type, string_adaptor>& context) const { return evaluate(context).asBool(); }
-  virtual double evaluateAsNumber(const DOM::Node<string_type, string_adaptor>& context) const { return evaluate(context).asNumber(); }
-  virtual string_type evaluateAsString(const DOM::Node<string_type, string_adaptor>& context) const { return evaluate(context).asString(); }
-  virtual NodeSet<string_type, string_adaptor> evaluateAsNodeSet(const DOM::Node<string_type, string_adaptor>& context) const { return evaluate(context).asNodeSet(); }
-
-  virtual XPathValue<string_type, string_adaptor> evaluate(const DOM::Node<string_type, string_adaptor>& context, 
+   virtual XPathValue<string_type, string_adaptor> evaluate(const DOM::Node<string_type, string_adaptor>& context, 
                                               const ExecutionContext<string_type, string_adaptor>& executionContext) const = 0;
 
   virtual bool evaluateAsBool(const DOM::Node<string_type, string_adaptor>& context, 
-															const ExecutionContext<string_type, string_adaptor>& executionContext) const { return evaluate(context, executionContext).asBool(); }
+															const ExecutionContext<string_type, string_adaptor>& executionContext) const 
+  { 
+    return evaluate(context, executionContext).asBool(); 
+  }
   virtual double evaluateAsNumber(const DOM::Node<string_type, string_adaptor>& context, 
-                                  const ExecutionContext<string_type, string_adaptor>& executionContext) const { return evaluate(context, executionContext).asNumber(); }
+                                  const ExecutionContext<string_type, string_adaptor>& executionContext) const 
+  { 
+    return evaluate(context, executionContext).asNumber(); 
+  }
   virtual string_type evaluateAsString(const DOM::Node<string_type, string_adaptor>& context, 
-                                       const ExecutionContext<string_type, string_adaptor>& executionContext) const { return evaluate(context, executionContext).asString(); }
+                                       const ExecutionContext<string_type, string_adaptor>& executionContext) const 
+  { 
+    return evaluate(context, executionContext).asString(); 
+  }
   virtual NodeSet<string_type, string_adaptor> evaluateAsNodeSet(const DOM::Node<string_type, string_adaptor>& context, 
-                                                 const ExecutionContext<string_type, string_adaptor>& executionContext) const { return evaluate(context, executionContext).asNodeSet(); }
+                                                 const ExecutionContext<string_type, string_adaptor>& executionContext) const 
+  {
+    return evaluate(context, executionContext).asNodeSet(); 
+  }
 
   virtual void scan(impl::Expression_scanner<string_type, string_adaptor>& scanner) const { scanner.scan(this); }
 
 private:
+  static const ExecutionContext<string_type, string_adaptor>& StaticExecutionContext() 
+  {
+    static ExecutionContext<string_type, string_adaptor> executionContext;
+    return executionContext;
+  } // StaticExecutionContext
+
   XPathExpression_impl(const XPathExpression_impl&);
   bool operator==(const XPathExpression_impl&);
   XPathExpression_impl& operator=(const XPathExpression_impl&);
diff --git a/include/XPath/impl/xpath_value.hpp b/include/XPath/impl/xpath_value.hpp
index a2101314..31701ca6 100644
--- a/include/XPath/impl/xpath_value.hpp
+++ b/include/XPath/impl/xpath_value.hpp
@@ -14,8 +14,43 @@ namespace Arabica
 namespace XPath
 {
 
+template<class string_type, class string_adaptor>
+class Value_base : public XPathValue_impl<string_type, string_adaptor>, public XPathExpression_impl<string_type, string_adaptor>
+{
+protected:
+  Value_base() { }
+  ~Value_base() { }
+
+public:
+  virtual bool evaluateAsBool(const DOM::Node<string_type, string_adaptor>& context) { return asBool(); }
+  virtual double evaluateAsNumber(const DOM::Node<string_type, string_adaptor>& context) { return asNumber(); }
+  virtual string_type evaluateAsString(const DOM::Node<string_type, string_adaptor>& context) { return asString(); }
+  virtual NodeSet<string_type, string_adaptor> evaluateAsNodeSet(const DOM::Node<string_type, string_adaptor>& context) { return asNodeSet(); }
+
+  virtual bool evaluateAsBool(const DOM::Node<string_type, string_adaptor>& context, 
+															const ExecutionContext<string_type, string_adaptor>& executionContext) const 
+  { 
+    return asBool(); 
+  }
+  virtual double evaluateAsNumber(const DOM::Node<string_type, string_adaptor>& context, 
+                                  const ExecutionContext<string_type, string_adaptor>& executionContext) const 
+  { 
+    return asNumber(); 
+  }
+  virtual string_type evaluateAsString(const DOM::Node<string_type, string_adaptor>& context, 
+                                       const ExecutionContext<string_type, string_adaptor>& executionContext) const 
+  { 
+    return asString(); 
+  }
+  virtual NodeSet<string_type, string_adaptor> evaluateAsNodeSet(const DOM::Node<string_type, string_adaptor>& context, 
+                                                 const ExecutionContext<string_type, string_adaptor>& executionContext) const 
+  {
+    return asNodeSet(); 
+  }
+}; // class Value_base
+
 template<class string_type, class string_adaptor = Arabica::default_string_adaptor<string_type> >
-class BoolValue : public XPathValue_impl<string_type, string_adaptor>, public XPathExpression_impl<string_type, string_adaptor>
+class BoolValue : public Value_base<string_type, string_adaptor>
 {
 public:
   BoolValue(bool value) :
@@ -28,10 +63,6 @@ public:
   {
     return XPathValue<string_type, string_adaptor>(new BoolValue(value_));
   } // evaluate
-  virtual bool evaluateAsBool(const DOM::Node<string_type, string_adaptor>& context) { return asBool(); }
-  virtual double evaluateAsNumber(const DOM::Node<string_type, string_adaptor>& context) { return asNumber(); }
-  virtual string_type evaluateAsString(const DOM::Node<string_type, string_adaptor>& context) { return asString(); }
-  virtual NodeSet<string_type, string_adaptor> evaluateAsNodeSet(const DOM::Node<string_type, string_adaptor>& context) { return asNodeSet(); }
 
   virtual bool asBool() const { return value_; }
   virtual double asNumber() const { return value_ ? 1 : 0; }
@@ -45,7 +76,7 @@ private:
 }; // class BoolValue
 
 template<class string_type, class string_adaptor = Arabica::default_string_adaptor<string_type> >
-class NumericValue : public XPathValue_impl<string_type, string_adaptor>, public XPathExpression_impl<string_type, string_adaptor>
+class NumericValue : public Value_base<string_type, string_adaptor>
 {
 public:
   NumericValue(double value) :
@@ -58,10 +89,6 @@ public:
   {
     return createValue(value_);
   } // evaluate
-  virtual bool evaluateAsBool(const DOM::Node<string_type, string_adaptor>& context) { return asBool(); }
-  virtual double evaluateAsNumber(const DOM::Node<string_type, string_adaptor>& context) { return asNumber(); }
-  virtual string_type evaluateAsString(const DOM::Node<string_type, string_adaptor>& context) { return asString(); }
-  virtual NodeSet<string_type, string_adaptor> evaluateAsNodeSet(const DOM::Node<string_type, string_adaptor>& context) { return asNodeSet(); }
 
   virtual bool asBool() const 
   { 
@@ -89,7 +116,7 @@ private:
 }; // class NumberValue
 
 template<class string_type, class string_adaptor = Arabica::default_string_adaptor<string_type> >
-class StringValue : public XPathValue_impl<string_type, string_adaptor>, public XPathExpression_impl<string_type, string_adaptor>
+class StringValue : public Value_base<string_type, string_adaptor>
 {
 public:
   StringValue(const char* value) :
@@ -104,10 +131,6 @@ public:
   {
     return XPathValue<string_type, string_adaptor>(new StringValue(value_));
   } // evaluate
-  virtual bool evaluateAsBool(const DOM::Node<string_type, string_adaptor>& context) { return asBool(); }
-  virtual double evaluateAsNumber(const DOM::Node<string_type, string_adaptor>& context) { return asNumber(); }
-  virtual string_type evaluateAsString(const DOM::Node<string_type, string_adaptor>& context) { return asString(); }
-  virtual NodeSet<string_type, string_adaptor> evaluateAsNodeSet() const { return asNodeSet(); }
 
   virtual bool asBool() const { return !string_adaptor::empty(value_); }
   virtual double asNumber() const 
@@ -124,7 +147,7 @@ private:
 }; // class StringValue
 
 template<class string_type, class string_adaptor = Arabica::default_string_adaptor<string_type> >
-class NodeSetValue : public XPathValue_impl<string_type, string_adaptor>, public XPathExpression_impl<string_type, string_adaptor>
+class NodeSetValue : public Value_base<string_type, string_adaptor>
 {
 public:
   NodeSetValue(const NodeSet<string_type, string_adaptor>& set) : set_(set) { }
@@ -139,10 +162,6 @@ public:
   {
     return XPathValue<string_type, string_adaptor>(this);
   } // evaluate
-  virtual bool evaluateAsBool(const DOM::Node<string_type, string_adaptor>& context) const{ return asBool(); }
-  virtual double evaluateAsNumber(const DOM::Node<string_type, string_adaptor>& context) const { return asNumber(); }
-  virtual string_type evaluateAsString(const DOM::Node<string_type, string_adaptor>& context) const { return asString(); }
-  virtual const NodeSet<string_type, string_adaptor>& evaluateAsNodeSet() const { return asNodeSet(); }
 
   virtual bool asBool() const 
   {