diff --git a/vlsisapd/src/dtr/src/PyTechno.cpp b/vlsisapd/src/dtr/src/PyTechno.cpp
index e5aeb0b2..32eb040c 100644
--- a/vlsisapd/src/dtr/src/PyTechno.cpp
+++ b/vlsisapd/src/dtr/src/PyTechno.cpp
@@ -12,6 +12,13 @@ void translator(DTRException const& e) {
     PyErr_SetString(PyExc_UserWarning, e.what());
 }
 
+
+// specify that Techno::getValue & Techno::getValueAsString methods have optional arguments
+BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(getValue_overloads        , getValue        , 1, 3);
+BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(getValueAsString_overloads, getValueAsString, 1, 3);
+// specify that Techno::addRule method has optional arguments
+BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(addRule_overloads, addRule, 3, 5);
+
 BOOST_PYTHON_MODULE(pyDTR) {
     // class DTR::Name
     class_<Name>("Name", init<std::string>())
@@ -19,7 +26,7 @@ BOOST_PYTHON_MODULE(pyDTR) {
     ;
 
     // class DTR::Rule
-    class_<Rule>("Rule", init<Name, double, Name, Name, Name, Name>())
+    class_<Rule>("Rule", init<Name, double, Name, Name, Name>())
         // accessors
         .def("getName"         , &Rule::getName         )
         .def("getType"         , &Rule::getType         )
@@ -28,27 +35,31 @@ BOOST_PYTHON_MODULE(pyDTR) {
         .def("getRef"          , &Rule::getRef          )
         .def("getLayer1"       , &Rule::getLayer1       )
         .def("getLayer2"       , &Rule::getLayer2       )
+
         // modifiers
         .def("setType"         , &Rule::setType         )
     ; 
 
     // class DTR::ARule derived from DTR::Rule
-    class_<ARule, bases<Rule> >("ARule", init<Name, double, Name, Name, Name, Name>())
+    class_<ARule, bases<Rule> >("ARule", init<Name, double, Name, Name, Name>())
     ;
 
     // class DTR::Techno
     class_<Techno>("Techno", init<Name, Name>())
+        // accessors
+        .def("getName"         , &Techno::getName)
+        .def("getUnit"         , &Techno::getUnit)
+        .def("getValue"        , &Techno::getValue, getValue_overloads())
+        .def("getValueAsString", &Techno::getValueAsString, getValueAsString_overloads())
+        
+        // modifiers
+        .def("addRule"         , &Techno::addRule , addRule_overloads()[return_value_policy<reference_existing_object>()])
+        .def("addARule"        , &Techno::addARule, return_value_policy<reference_existing_object>())
+
+        // others
         .def("readFromFile", &Techno::readFromFile, return_value_policy<manage_new_object>())
         .staticmethod("readFromFile")
-
-        .def("getName"         , &Techno::getName )
-        .def("getUnit"         , &Techno::getUnit )
-        .def("getValue"        , static_cast<double(Techno::*)(Name            )>(&Techno::getValue))
-        .def("getValue"        , static_cast<double(Techno::*)(Name, Name      )>(&Techno::getValue))
-        .def("getValue"        , static_cast<double(Techno::*)(Name, Name, Name)>(&Techno::getValue))
-        .def("getValueAsString", static_cast<string(Techno::*)(Name            )>(&Techno::getValueAsString))
-        .def("getValueAsString", static_cast<string(Techno::*)(Name, Name      )>(&Techno::getValueAsString))
-        .def("getValueAsString", static_cast<string(Techno::*)(Name, Name, Name)>(&Techno::getValueAsString))
+        .def("writeToFile" , &Techno::writeToFile)
     ;
 
     // DTRException translator
diff --git a/vlsisapd/src/dtr/src/Techno.cpp b/vlsisapd/src/dtr/src/Techno.cpp
index 346de4e1..ffba92ce 100644
--- a/vlsisapd/src/dtr/src/Techno.cpp
+++ b/vlsisapd/src/dtr/src/Techno.cpp
@@ -34,26 +34,18 @@ namespace {
 namespace DTR {
 Techno::Techno(Name name, Name unit) : _name(name), _unit(unit) {}
 
-Rule* Techno::addRule (Name name, double value, Name valueStr, Name ref, Name layer1, Name layer2) {
-    Rule* rule = new Rule(name, value, valueStr, ref, layer1, layer2);
+Rule* Techno::addRule (Name name, double value, Name ref, Name layer1, Name layer2) {
+    Rule* rule = new Rule(name, value, ref, layer1, layer2);
     _rules.push_back(rule);
     return rule;
 }
 
-ARule* Techno::addARule (Name name, double value, Name valueStr, Name ref, Name layer1, Name layer2) {
-    ARule* arule = new ARule(name, value, valueStr, ref, layer1, layer2);
+ARule* Techno::addARule (Name name, double value, Name ref, Name layer1, Name layer2) {
+    ARule* arule = new ARule(name, value, ref, layer1, layer2);
     _rules.push_back(arule);
     return arule;
 }
 
-double Techno::getValue(Name name) {
-    return getValue(name, Name(""), Name(""));
-}
-
-double Techno::getValue(Name name, Name layer) {
-    return getValue(name, layer, Name(""));
-}
-
 double Techno::getValue(Name name, Name layer1, Name layer2) {
     bool testL1   = (layer1 == Name("")) ? false : true;
     bool testL2   = (layer2 == Name("")) ? false : true;
@@ -86,14 +78,6 @@ double Techno::getValue(Name name, Name layer1, Name layer2) {
     throw DTRException(error);
 }
 
-string Techno::getValueAsString(Name name) {
-    return getValueAsString(name, Name(""), Name(""));
-}
-
-string Techno::getValueAsString(Name name, Name layer) {
-    return getValueAsString(name, layer, Name(""));
-}
-
 string Techno::getValueAsString(Name name, Name layer1, Name layer2) {
     bool testL1   = (layer1 == Name("")) ? false : true;
     bool testL2   = (layer2 == Name("")) ? false : true;
@@ -176,21 +160,18 @@ Techno* Techno::readFromFile(const string filePath) {
                                 Name layer1 ((const char*)layer1C);
                                 Name layer2 ((const char*)layer2C);
                                 double value = ::getValue<double>(valueC);
-                                Name valueStr ((const char*)valueC);
-                                rule = techno->addRule(name, value, valueStr, ref, layer1, layer2);
+                                rule = techno->addRule(name, value, ref, layer1, layer2);
                             } else if (nameC && layerC && valueC && refC) {// rule with only one layer
                                 Name name  ((const char*)nameC);
                                 Name ref   ((const char*)refC);
                                 Name layer ((const char*)layerC);
                                 double value = ::getValue<double>(valueC);
-                                Name valueStr ((const char*)valueC);
-                                rule = techno->addRule(name, value, valueStr, ref, layer);
+                                rule = techno->addRule(name, value, ref, layer);
                             } else if (nameC && valueC && refC) { // rule without layer
                                 Name name ((const char*)nameC);
                                 Name ref  ((const char*)refC);
                                 double value = ::getValue<double>(valueC);
-                                Name valueStr ((const char*)valueC);
-                                rule = techno->addRule(name, value, valueStr, ref);
+                                rule = techno->addRule(name, value, ref);
                             } else { // invalid case
                                 throw DTRException("[ERROR] properties of 'rule' node must be ('name', 'value', 'ref') or ('name', 'layer', 'value', 'ref') or ('name', 'layer1', 'layer2', 'value', 'ref').");
                                 return NULL;
@@ -211,8 +192,7 @@ Techno* Techno::readFromFile(const string filePath) {
                                 Name layer2 ((const char*)layer2C);
                                 Name ref    ((const char*)refC);
                                 double value = ::getValue<double>(valueC);
-                                Name valueStr ((const char*)valueC);
-                                techno->addARule(name, value, valueStr, ref, layer1, layer2);
+                                techno->addARule(name, value, ref, layer1, layer2);
                             } else {
                                 throw DTRException("[ERROR] 'arule' node must have 'name', 'layer1', 'layer2', 'value' and 'ref' properties.");
                                 return NULL;
diff --git a/vlsisapd/src/dtr/src/vlsisapd/dtr/Rules.h b/vlsisapd/src/dtr/src/vlsisapd/dtr/Rules.h
index cf1dedfc..659b8db1 100644
--- a/vlsisapd/src/dtr/src/vlsisapd/dtr/Rules.h
+++ b/vlsisapd/src/dtr/src/vlsisapd/dtr/Rules.h
@@ -10,13 +10,23 @@
 #ifndef __DTR_RULES_H__
 #define __DTR_RULES_H__
 
+#include <string>
+#include <sstream>
+
 #include "vlsisapd/dtr/Name.h"
 
 namespace DTR {
+template <typename T>
+std::string to_string(T const& value) {
+    std::stringstream sstr;
+    sstr << value;
+    return sstr.str();
+}
+
 class Rule {
     public:
-    Rule(Name name, double value, Name valueStr, Name ref, Name layer1, Name layer2)
-        : _name(name), _type(Name("")), _value(value), _valueStr(valueStr), _ref(ref), _layer1(layer1), _layer2(layer2) {};
+    Rule(Name name, double value, Name ref, Name layer1, Name layer2)
+        : _name(name), _type(Name("")), _value(value), _valueStr(to_string(value)), _ref(ref), _layer1(layer1), _layer2(layer2) {};
     
     // accessors
     inline Name   getName();
@@ -43,8 +53,8 @@ class Rule {
 
 class ARule : public Rule {
     public:
-    ARule(Name name, double value, Name valueStr, Name ref, Name layer1, Name layer2)
-        : Rule(name, value, valueStr, ref, layer1, layer2) {};
+    ARule(Name name, double value, Name ref, Name layer1, Name layer2)
+        : Rule(name, value, ref, layer1, layer2) {};
 };
     
 inline Name   Rule::getName()   { return _name;   };
diff --git a/vlsisapd/src/dtr/src/vlsisapd/dtr/Techno.h b/vlsisapd/src/dtr/src/vlsisapd/dtr/Techno.h
index 9808cd6a..e3edb351 100644
--- a/vlsisapd/src/dtr/src/vlsisapd/dtr/Techno.h
+++ b/vlsisapd/src/dtr/src/vlsisapd/dtr/Techno.h
@@ -28,16 +28,11 @@ class Techno {
     inline Name getUnit();
     inline std::vector<Rule*>&  getRules();
 
-    Rule*  addRule (Name name, double value, Name valueStr, Name ref, Name layer1=Name(""), Name layer2=Name(""));
-    ARule* addARule(Name name, double value, Name valueStr, Name ref, Name layer1         , Name layer2);
+    Rule*  addRule (Name name, double value, Name ref, Name layer1=Name(""), Name layer2=Name(""));
+    ARule* addARule(Name name, double value, Name ref, Name layer1         , Name layer2);
 
-    double getValue(Name name);
-    double getValue(Name name, Name layer);
-    double getValue(Name name, Name layer1, Name layer2);
-    
-    std::string getValueAsString(Name name);
-    std::string getValueAsString(Name name, Name layer);
-    std::string getValueAsString(Name name, Name layer1, Name layer2);
+    double getValue(Name name, Name layer1=Name(""), Name layer2=Name(""));
+    std::string getValueAsString(Name name, Name layer1=Name(""), Name layer2=Name(""));
     
     bool writeToFile(std::string filePath);
     static Techno* readFromFile(const std::string filePath);