diff --git a/src/rdb/rdb/rdb.cc b/src/rdb/rdb/rdb.cc
index 2d77e5c46..807d0c668 100644
--- a/src/rdb/rdb/rdb.cc
+++ b/src/rdb/rdb/rdb.cc
@@ -60,16 +60,18 @@ namespace rdb
 //  type index specializations
 
 template <> RDB_PUBLIC int type_index_of<double> ()        { return 0; }
-template <> RDB_PUBLIC int type_index_of<std::string> ()   { return 1; }
-template <> RDB_PUBLIC int type_index_of<db::DPolygon> ()  { return 2; }
-template <> RDB_PUBLIC int type_index_of<db::DEdge> ()     { return 3; }
-template <> RDB_PUBLIC int type_index_of<db::DEdgePair> () { return 4; }
-template <> RDB_PUBLIC int type_index_of<db::DBox> ()      { return 5; }
-template <> RDB_PUBLIC int type_index_of<db::DPath> ()     { return 6; }
-template <> RDB_PUBLIC int type_index_of<db::DText> ()     { return 7; }
+template <> RDB_PUBLIC int type_index_of<int> ()           { return 1; }
+template <> RDB_PUBLIC int type_index_of<std::string> ()   { return 2; }
+template <> RDB_PUBLIC int type_index_of<db::DPolygon> ()  { return 3; }
+template <> RDB_PUBLIC int type_index_of<db::DEdge> ()     { return 4; }
+template <> RDB_PUBLIC int type_index_of<db::DEdgePair> () { return 5; }
+template <> RDB_PUBLIC int type_index_of<db::DBox> ()      { return 6; }
+template <> RDB_PUBLIC int type_index_of<db::DPath> ()     { return 7; }
+template <> RDB_PUBLIC int type_index_of<db::DText> ()     { return 8; }
 
 //  Explicit instantiations to make VC++ happy in debug mode
 template class RDB_PUBLIC Value<double>;
+template class RDB_PUBLIC Value<int>;
 template class RDB_PUBLIC Value<std::string>;
 template class RDB_PUBLIC Value<db::DPolygon>;
 template class RDB_PUBLIC Value<db::DEdge>;
@@ -85,6 +87,11 @@ template <> RDB_PUBLIC std::string Value<double>::to_string () const
   return "float: " + tl::to_string (m_value);
 }
 
+template <> RDB_PUBLIC std::string Value<int>::to_string () const
+{
+  return "int: " + tl::to_string (m_value);
+}
+
 template <> RDB_PUBLIC std::string Value<std::string>::to_string () const
 {
   return "text: " + tl::to_word_or_quoted_string (m_value);
@@ -127,6 +134,11 @@ template <> RDB_PUBLIC std::string Value<double>::to_display_string () const
   return tl::to_string (m_value);
 }
 
+template <> RDB_PUBLIC std::string Value<int>::to_display_string () const
+{
+  return tl::to_string (m_value);
+}
+
 template <> RDB_PUBLIC std::string Value<std::string>::to_display_string () const
 {
   return m_value;
@@ -169,6 +181,11 @@ template <> RDB_PUBLIC bool Value<double>::is_shape () const
   return false;
 }
 
+template <> RDB_PUBLIC bool Value<int>::is_shape () const
+{
+  return false;
+}
+
 template <> RDB_PUBLIC bool Value<std::string>::is_shape () const
 {
   return false;
@@ -420,7 +437,7 @@ Values::compare (const Values &other, const std::map<id_type, id_type> &tag_map,
     }
 
     id_type t2 = 0;
-    while (b != end () && b->tag_id () != 0) {
+    while (b != other.end () && b->tag_id () != 0) {
       auto j = rev_tag_map.find (b->tag_id ());
       if (j != rev_tag_map.end ()) {
         t2 = j->first;
@@ -438,18 +455,21 @@ Values::compare (const Values &other, const std::map<id_type, id_type> &tag_map,
     }
 
     if (a->get () && b->get ()) {
-      if (a->get ()->compare (b->get ())) {
+      if (rdb::ValueBase::compare (a->get (), b->get ())) {
         return true;
-      } else if (b->get ()->compare (a->get ())) {
+      } else if (rdb::ValueBase::compare (b->get (), a->get ())) {
         return false;
       }
     } else if ((a->get () != 0) != (b->get () != 0)) {
       return (a->get () != 0) < (b->get () != 0);
     }
 
+    ++a;
+    ++b;
+
   }
 
-  return false;
+  return b != other.end ();
 }
 
 std::string 
diff --git a/src/rdb/rdb/rdb.h b/src/rdb/rdb/rdb.h
index 936ab28e6..3541e6768 100644
--- a/src/rdb/rdb/rdb.h
+++ b/src/rdb/rdb/rdb.h
@@ -752,6 +752,14 @@ public:
     m_values.swap (other.m_values);
   }
 
+  /**
+   *  @brief Clears the values
+   */
+  void clear ()
+  {
+    m_values.clear ();
+  }
+
   /**
    *  @brief Convert the values collection to a string 
    */
diff --git a/src/rdb/unit_tests/rdbTests.cc b/src/rdb/unit_tests/rdbTests.cc
index 55e78c1f9..5665aa522 100644
--- a/src/rdb/unit_tests/rdbTests.cc
+++ b/src/rdb/unit_tests/rdbTests.cc
@@ -598,3 +598,226 @@ TEST(7)
 
 #endif
 }
+
+
+TEST(8_ApplyBasicEmptyValue)
+{
+  rdb::Database db1;
+  rdb::Category *cat1 = db1.create_category ("cat_name");
+  rdb::Cell *c1 = db1.create_cell ("cell");
+  rdb::Item *i1 = db1.create_item (c1->id (), cat1->id ());
+
+  rdb::Database db2;
+  db2.create_category ("dummy_cat");
+  rdb::Category *cat2 = db2.create_category ("cat_name");
+  db2.create_cell ("dummy_cell");
+  rdb::Cell *c2 = db2.create_cell ("cell");
+  rdb::Item *i2 = db2.create_item (c2->id (), cat2->id ());
+
+  rdb::id_type tag2 = db2.tags ().tag ("tag2").id ();
+  i2->add_tag (tag2);
+
+  EXPECT_EQ (i2->tag_str (), "tag2");
+  EXPECT_EQ (i1->tag_str (), "");
+
+  //  empty value apply
+  db1.apply (db2);
+
+  EXPECT_EQ (i1->tag_str (), "tag2");
+}
+
+TEST(9_ApplyBasicSomeValue)
+{
+  rdb::Database db1;
+  rdb::Category *cat1 = db1.create_category ("cat_name");
+  rdb::Cell *c1 = db1.create_cell ("cell");
+  rdb::Item *i1 = db1.create_item (c1->id (), cat1->id ());
+  i1->add_value (std::string ("abc"));
+
+  rdb::Database db2;
+  db2.create_category ("dummy_cat");
+  rdb::Category *cat2 = db2.create_category ("cat_name");
+  db2.create_cell ("dummy_cell");
+  rdb::Cell *c2 = db2.create_cell ("cell");
+  rdb::Item *i2 = db2.create_item (c2->id (), cat2->id ());
+
+  db2.tags ().tag ("dummy_tag");
+  rdb::id_type tag2 = db2.tags ().tag ("tag2").id ();
+  i2->add_tag (tag2);
+
+  EXPECT_EQ (i2->tag_str (), "tag2");
+  EXPECT_EQ (i1->tag_str (), "");
+
+  //  empty value apply
+  db1.apply (db2);
+
+  //  not applied (different value)
+  EXPECT_EQ (i1->tag_str (), "");
+
+  //  incorrect value
+  i2->add_value (17);
+
+  db1.apply (db2);
+
+  //  still not applied
+  EXPECT_EQ (i1->tag_str (), "");
+
+  //  correct value
+  i2->values ().clear ();
+  i2->add_value (std::string ("abc"));
+
+  db1.apply (db2);
+
+  //  now, the tag is applied
+  EXPECT_EQ (i1->tag_str (), "tag2");
+
+  //  too many values
+  i1->remove_tags ();
+  i2->add_value (17);
+
+  db1.apply (db2);
+
+  // not applied
+  EXPECT_EQ (i1->tag_str (), "");
+}
+
+TEST(10_ApplyTaggedValue)
+{
+  rdb::Database db1;
+  rdb::Category *cat1 = db1.create_category ("cat_name");
+  rdb::Cell *c1 = db1.create_cell ("cell");
+  rdb::Item *i1 = db1.create_item (c1->id (), cat1->id ());
+  rdb::id_type vtag11 = db1.tags ().tag ("vtag1").id ();
+  rdb::id_type vtag12 = db1.tags ().tag ("vtag2").id ();
+  i1->add_value (std::string ("abc"));
+
+  rdb::Database db2;
+  db2.create_category ("dummy_cat");
+  rdb::Category *cat2 = db2.create_category ("cat_name");
+  db2.create_cell ("dummy_cell");
+  rdb::Cell *c2 = db2.create_cell ("cell");
+  rdb::Item *i2 = db2.create_item (c2->id (), cat2->id ());
+  db2.tags ().tag ("dummy_tag");
+
+  rdb::id_type tag2 = db2.tags ().tag ("tag2").id ();
+  rdb::id_type vtag21 = db2.tags ().tag ("vtag1").id ();
+  i2->add_tag (tag2);
+  i2->add_value (std::string ("abc"), vtag21);
+
+  //  empty tag vs. vtag1
+  db1.apply (db2);
+
+  //  not applied (empty tag vs. tagged)
+  EXPECT_EQ (i1->tag_str (), "");
+
+  //  vtag2 vs. vtag1
+  i1->values ().clear ();
+  i1->add_value (std::string ("abc"), vtag12);
+
+  db1.apply (db2);
+
+  //  not applied (different tags)
+  EXPECT_EQ (i1->tag_str (), "");
+
+  //  vtag1 vs. vtag1
+  i1->values ().clear ();
+  i1->add_value (std::string ("abc"), vtag11);
+
+  db1.apply (db2);
+
+  //  this time it is applied (same tag)
+  EXPECT_EQ (i1->tag_str (), "tag2");
+}
+
+TEST(11_ApplyWrongCat)
+{
+  rdb::Database db1;
+  rdb::Category *cat1 = db1.create_category ("cat_name");
+  rdb::Cell *c1 = db1.create_cell ("cell");
+  rdb::Item *i1 = db1.create_item (c1->id (), cat1->id ());
+
+  rdb::Database db2;
+  db2.create_category ("dummy_cat");
+  rdb::Category *cat2 = db2.create_category ("xcat_name");
+  db2.create_cell ("dummy_cell");
+  rdb::Cell *c2 = db2.create_cell ("cell");
+  rdb::Item *i2 = db2.create_item (c2->id (), cat2->id ());
+
+  rdb::id_type tag2 = db2.tags ().tag ("tag2").id ();
+  i2->add_tag (tag2);
+
+  EXPECT_EQ (i2->tag_str (), "tag2");
+  EXPECT_EQ (i1->tag_str (), "");
+
+  //  empty value apply
+  db1.apply (db2);
+
+  EXPECT_EQ (i1->tag_str (), "");
+}
+
+TEST(12_ApplyWrongCell)
+{
+  rdb::Database db1;
+  rdb::Category *cat1 = db1.create_category ("cat_name");
+  rdb::Cell *c1 = db1.create_cell ("cell");
+  rdb::Item *i1 = db1.create_item (c1->id (), cat1->id ());
+
+  rdb::Database db2;
+  db2.create_category ("dummy_cat");
+  rdb::Category *cat2 = db2.create_category ("cat_name");
+  db2.create_cell ("dummy_cell");
+  rdb::Cell *c2 = db2.create_cell ("xcell");
+  rdb::Item *i2 = db2.create_item (c2->id (), cat2->id ());
+
+  rdb::id_type tag2 = db2.tags ().tag ("tag2").id ();
+  i2->add_tag (tag2);
+
+  EXPECT_EQ (i2->tag_str (), "tag2");
+  EXPECT_EQ (i1->tag_str (), "");
+
+  //  empty value apply
+  db1.apply (db2);
+
+  EXPECT_EQ (i1->tag_str (), "");
+}
+
+TEST(13_ApplyIgnoreUnknownTag)
+{
+  rdb::Database db1;
+  rdb::Category *cat1 = db1.create_category ("cat_name");
+  rdb::Cell *c1 = db1.create_cell ("cell");
+  rdb::Item *i1 = db1.create_item (c1->id (), cat1->id ());
+  rdb::id_type vtag11 = db1.tags ().tag ("vtag1").id ();
+  i1->add_value (std::string ("abc"), vtag11);
+
+  rdb::Database db2;
+  db2.create_category ("dummy_cat");
+  rdb::Category *cat2 = db2.create_category ("cat_name");
+  db2.create_cell ("dummy_cell");
+  rdb::Cell *c2 = db2.create_cell ("cell");
+  rdb::Item *i2 = db2.create_item (c2->id (), cat2->id ());
+  db2.tags ().tag ("dummy_tag");
+
+  rdb::id_type tag2 = db2.tags ().tag ("tag2").id ();
+  rdb::id_type vtag21 = db2.tags ().tag ("vtag1").id ();
+  rdb::id_type vtag22 = db2.tags ().tag ("vtag2").id ();
+  i2->add_tag (tag2);
+
+  //  same tags, different values
+  i2->add_value (std::string ("xyz"), vtag21);
+
+  db1.apply (db2);
+
+  //  not applied
+  EXPECT_EQ (i1->tag_str (), "");
+
+  //  different tags without mapping
+  i2->values ().clear ();
+  i2->add_value (std::string ("xyz"), vtag22);
+
+  //  values with incompatible tags are ignored -> tag2 is applied
+  db1.apply (db2);
+
+  EXPECT_EQ (i1->tag_str (), "tag2");
+}
+