From 2aa3cabf1b737e225178230882ee9aadfd817ce0 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 28 Mar 2013 16:04:48 +0200
Subject: Add changelog support for add/drop index/foreign key

Also diagnose changes to primary keys and establish the 'alters'
association.
---
 odb/relational/changelog.cxx             | 357 +++++++++++++++++++++++++++++--
 odb/semantics/relational/changelog.cxx   |  84 +++++++-
 odb/semantics/relational/changeset.cxx   |  10 +-
 odb/semantics/relational/changeset.hxx   |   4 +-
 odb/semantics/relational/column.cxx      |  29 ++-
 odb/semantics/relational/column.hxx      |  58 +++--
 odb/semantics/relational/elements.cxx    |  38 +++-
 odb/semantics/relational/elements.hxx    |  95 +++++++-
 odb/semantics/relational/elements.txx    |  39 +++-
 odb/semantics/relational/foreign-key.cxx |  81 ++++++-
 odb/semantics/relational/foreign-key.hxx |  48 +++++
 odb/semantics/relational/index.cxx       |  75 ++++++-
 odb/semantics/relational/index.hxx       |  48 ++++-
 odb/semantics/relational/key.cxx         |   4 +-
 odb/semantics/relational/key.hxx         |  14 +-
 odb/semantics/relational/model.cxx       |   4 +-
 odb/semantics/relational/name.hxx        |  12 ++
 odb/semantics/relational/table.cxx       |  33 ++-
 odb/semantics/relational/table.hxx       |  18 +-
 odb/traversal/relational/foreign-key.hxx |   3 +
 odb/traversal/relational/index.hxx       |   2 +
 21 files changed, 927 insertions(+), 129 deletions(-)

diff --git a/odb/relational/changelog.cxx b/odb/relational/changelog.cxx
index 530c3a0..2208078 100644
--- a/odb/relational/changelog.cxx
+++ b/odb/relational/changelog.cxx
@@ -26,7 +26,10 @@ namespace relational
       // diff
       //
 
-      struct diff_table: trav_rel::column
+      struct diff_table: trav_rel::column,
+                         trav_rel::primary_key,
+                         trav_rel::foreign_key,
+                         trav_rel::index
       {
         enum mode_type {mode_add, mode_drop};
 
@@ -43,20 +46,28 @@ namespace relational
             if (column* oc = other.find<column> (c.name ()))
             {
               if (c.type () != oc->type ())
-                diagnose_unsupported (c, "type");
+                diagnose_column (c, "type", oc->type (), c.type ());
 
               if (c.null () != oc->null ())
               {
                 alter_column& ac (g.new_node<alter_column> (c.id ()));
+
+                // Set the alters edge.
+                //
+                column* b (at.lookup<column, drop_column> (c.name ()));
+                assert (b != 0);
+                g.new_edge<alters> (ac, *b);
+
                 ac.null (c.null ());
                 g.new_edge<unames> (at, ac, c.name ());
               }
 
               if (c.default_ () != oc->default_ ())
-                diagnose_unsupported (c, "default value");
+                diagnose_column (
+                  c, "default value", oc->default_ (), c.default_ ());
 
               if (c.options () != oc->options ())
-                diagnose_unsupported (c, "options");
+                diagnose_column (c, "options", oc->options (), c.options ());
             }
             else
             {
@@ -66,7 +77,7 @@ namespace relational
           }
           else
           {
-            if (other.find<sema_rel::column> (c.name ()) == 0)
+            if (other.find<column> (c.name ()) == 0)
             {
               drop_column& dc (g.new_node<drop_column> (c.id ()));
               g.new_edge<unames> (at, dc, c.name ());
@@ -74,27 +85,244 @@ namespace relational
           }
         }
 
+        virtual void
+        traverse (sema_rel::primary_key& pk)
+        {
+          using sema_rel::primary_key;
+
+          if (mode == mode_add)
+          {
+            if (primary_key* opk = other.find<primary_key> (pk.name ()))
+            {
+              if (pk.auto_ () != opk->auto_ ())
+                diagnose_primary_key (pk, "auto kind");
+
+              if (pk.contains_size () != opk->contains_size ())
+                diagnose_primary_key (pk, "member set");
+
+              for (primary_key::contains_size_type i (0);
+                   i != pk.contains_size (); ++i)
+              {
+                sema_rel::contains& c (pk.contains_at (i));
+                sema_rel::contains& oc (opk->contains_at (i));
+
+                if (c.column ().name () != oc.column ().name ())
+                  diagnose_primary_key (pk, "member set");
+              }
+            }
+            else
+            {
+              location const& l (pk.get<location> ("cxx-location"));
+              error (l) << "adding object id to an existing class is " <<
+                "not supported" << endl;
+              info (l) << "consider re-implementing this change by adding " <<
+                "a new class with the object id, migrating the data, and " <<
+                "deleteing the old class" << endl;
+              throw operation_failed ();
+            }
+          }
+          else
+          {
+            if (other.find<primary_key> (pk.name ()) == 0)
+            {
+              location const& l (other.get<location> ("cxx-location"));
+              error (l) << "deleting object id from an existing class is " <<
+                "not supported" << endl;
+              info (l) << "consider re-implementing this change by adding " <<
+                "a new class without the object id, migrating the data, " <<
+                "and deleteing the old class" << endl;
+              throw operation_failed ();
+            }
+          }
+        }
+
+        virtual void
+        traverse (sema_rel::foreign_key& fk)
+        {
+          using sema_rel::foreign_key;
+
+          if (mode == mode_add)
+          {
+            if (foreign_key* ofk = other.find<foreign_key> (fk.name ()))
+            {
+              if (fk.deferred () != ofk->deferred ())
+                diagnose_foreign_key (fk, "deferred kind");
+
+              if (fk.on_delete () != ofk->on_delete ())
+                diagnose_foreign_key (fk, "on delete action");
+
+              if (fk.referenced_table () != ofk->referenced_table ())
+                diagnose_foreign_key (fk, "pointed-to class");
+
+              if (fk.referenced_columns () != ofk->referenced_columns ())
+                diagnose_foreign_key (fk, "id member set");
+
+              if (fk.contains_size () != ofk->contains_size ())
+                diagnose_foreign_key (fk, "id member set");
+
+              for (foreign_key::contains_size_type i (0);
+                   i != fk.contains_size (); ++i)
+              {
+                sema_rel::contains& c (fk.contains_at (i));
+                sema_rel::contains& oc (ofk->contains_at (i));
+
+                if (c.column ().name () != oc.column ().name ())
+                  diagnose_foreign_key (fk, "id member set");
+              }
+            }
+            else
+            {
+              add_foreign_key& afk (g.new_node<add_foreign_key> (fk, at, g));
+              g.new_edge<unames> (at, afk, fk.name ());
+            }
+          }
+          else
+          {
+            if (other.find<foreign_key> (fk.name ()) == 0)
+            {
+              drop_foreign_key& dfk (g.new_node<drop_foreign_key> (fk.id ()));
+              g.new_edge<unames> (at, dfk, fk.name ());
+            }
+          }
+        }
+
+        virtual void
+        traverse (sema_rel::index& i)
+        {
+          using sema_rel::index;
+
+          if (mode == mode_add)
+          {
+            if (index* oi = other.find<index> (i.name ()))
+            {
+              if (i.type () != oi->type ())
+                diagnose_index (i, "type", oi->type (), i.type ());
+
+              if (i.method () != oi->method ())
+                diagnose_index (i, "method", oi->method (), i.method ());
+
+              if (i.options () != oi->options ())
+                diagnose_index (i, "options", oi->options (), i.options ());
+
+              if (i.contains_size () != oi->contains_size ())
+                diagnose_index (i, "member set", "", "");
+
+              for (index::contains_size_type j (0);
+                   j != i.contains_size (); ++j)
+              {
+                sema_rel::contains& c (i.contains_at (j));
+                sema_rel::contains& oc (oi->contains_at (j));
+
+                if (c.column ().name () != oc.column ().name ())
+                  diagnose_index (i, "member set", "", "");
+
+                if (c.options () != oc.options ())
+                  diagnose_index (
+                    i, "member options", oc.options (), c.options ());
+              }
+            }
+            else
+            {
+              add_index& ai (g.new_node<add_index> (i, at, g));
+              g.new_edge<unames> (at, ai, i.name ());
+            }
+          }
+          else
+          {
+            if (other.find<index> (i.name ()) == 0)
+            {
+              drop_index& di (g.new_node<drop_index> (i.id ()));
+              g.new_edge<unames> (at, di, i.name ());
+            }
+          }
+        }
+
         void
-        diagnose_unsupported (sema_rel::column& c, char const* name)
+        diagnose_column (sema_rel::column& c,
+                         char const* name,
+                         string const& ov,
+                         string const& nv)
         {
           table& t (c.table ());
           location const& tl (t.get<location> ("cxx-location"));
           location const& cl (c.get<location> ("cxx-location"));
 
           error (cl) << "change to data member results in the change of " <<
-            "the corresponding column " << name << endl;
+            "the corresponding column " << name;
+
+          if (!ov.empty () || !nv.empty ())
+            cerr << " (old: '" << ov << "', new: '" << nv << "')";
+
+          cerr << endl;
+
           error (cl) << "this change is not yet handled automatically" << endl;
           info (cl) << "corresponding column '" << c.name () << "' " <<
             "originates here" << endl;
           info (tl) << "corresponding table '" << t.name () << "' " <<
             "originates here" << endl;
-          info (cl) << "consider re-implementing this change by creating " <<
+          info (cl) << "consider re-implementing this change by adding " <<
             "a new data member with the desired " << name << ", migrating " <<
             "the data, and deleting the old data member" << endl;
 
           throw operation_failed ();
         }
 
+        void
+        diagnose_primary_key (sema_rel::primary_key& pk, char const* name)
+        {
+          location const& l (pk.get<location> ("cxx-location"));
+
+          error (l) << "changing object id " << name << " in an existing " <<
+            "class is not supported" << endl;
+          info (l) << "consider re-implementing this change by adding " <<
+            "a new class with the desired object id " << name << ", " <<
+            "migrating the data, and deleteing the old class" << endl;
+
+          throw operation_failed ();
+        }
+
+        void
+        diagnose_foreign_key (sema_rel::foreign_key& fk, char const* name)
+        {
+          location const& l (fk.get<location> ("cxx-location"));
+
+          error (l) << "changing object pointer " << name << " is not " <<
+            "supported" << endl;
+          info (l) << "consider re-implementing this change by adding " <<
+            "a new object pointer with the desired " << name << ", " <<
+            "migrating the data, and deleteing the old pointer" << endl;
+
+          throw operation_failed ();
+        }
+
+        void
+        diagnose_index (sema_rel::index& i,
+                        char const* name,
+                        string const& ov,
+                        string const& nv)
+        {
+          table& t (i.table ());
+          location const& tl (t.get<location> ("cxx-location"));
+          location const& il (i.get<location> ("cxx-location"));
+
+          error (il) << "change to index " << name;
+
+          if (!ov.empty () || !nv.empty ())
+            cerr << " (old: '" << ov << "', new: '" << nv << "')";
+
+          cerr << " is not yet handled automatically" << endl;
+
+          info (il) << "corresponding index '" << i.name () << "' " <<
+            "originates here" << endl;
+          info (tl) << "corresponding table '" << t.name () << "' " <<
+            "originates here" << endl;
+          info (il) << "consider re-implementing this change by adding " <<
+            "a new index with the desired " << name << " and deleting the " <<
+            "old one" << endl;
+
+          throw operation_failed ();
+        }
+
       protected:
         table& other;
         mode_type mode;
@@ -122,6 +350,12 @@ namespace relational
               //
               alter_table& at (g.new_node<alter_table> (t.id ()));
 
+              // Set the alters edge for lookup.
+              //
+              table* bt (cs.lookup<table, drop_table> (t.name ()));
+              assert (bt != 0);
+              alters& ae (g.new_edge<alters> (at, *bt));
+
               {
                 trav_rel::table table;
                 trav_rel::unames names;
@@ -141,7 +375,10 @@ namespace relational
               if (!at.names_empty ())
                 g.new_edge<qnames> (cs, at, t.name ());
               else
+              {
+                g.delete_edge (at, *bt, ae);
                 g.delete_node (at);
+              }
             }
             else
             {
@@ -171,14 +408,21 @@ namespace relational
       // Assumes the new model has cxx-location set.
       //
       changeset&
-      diff (model& o, model& n, graph& g)
+      diff (model& o, model& n, changelog& l)
       {
-        changeset& r (g.new_node<changeset> (n.version ()));
+        changeset& r (l.new_node<changeset> (n.version ()));
+
+        // Set the alters edge for lookup.
+        //
+        l.new_edge<alters> (r,
+                            l.contains_changeset_empty ()
+                            ? static_cast<qscope&> (l.model ())
+                            : l.contains_changeset_back ().changeset ());
 
         {
           trav_rel::model model;
           trav_rel::qnames names;
-          diff_model dmodel (o, diff_model::mode_add, r, g);
+          diff_model dmodel (o, diff_model::mode_add, r, l);
           model >> names >> dmodel;
           model.traverse (n);
         }
@@ -186,7 +430,7 @@ namespace relational
         {
           trav_rel::model model;
           trav_rel::qnames names;
-          diff_model dmodel (n, diff_model::mode_drop, r, g);
+          diff_model dmodel (n, diff_model::mode_drop, r, l);
           model >> names >> dmodel;
           model.traverse (o);
         }
@@ -200,7 +444,11 @@ namespace relational
 
       struct patch_table: trav_rel::add_column,
                           trav_rel::drop_column,
-                          trav_rel::alter_column
+                          trav_rel::alter_column,
+                          trav_rel::add_index,
+                          trav_rel::drop_index,
+                          trav_rel::add_foreign_key,
+                          trav_rel::drop_foreign_key
       {
         patch_table (table& tl, graph& gr): t (tl), g (gr) {}
 
@@ -251,6 +499,74 @@ namespace relational
           }
         }
 
+        virtual void
+        traverse (sema_rel::add_index& ai)
+        {
+          using sema_rel::index;
+
+          try
+          {
+            index& i (g.new_node<index> (ai, t, g));
+            g.new_edge<unames> (t, i, ai.name ());
+          }
+          catch (duplicate_name const&)
+          {
+            cerr << "error: invalid changelog: index '" << ai.name () <<
+              "' already exists in table '" << t.name () << "'" << endl;
+            throw operation_failed ();
+          }
+        }
+
+        virtual void
+        traverse (sema_rel::drop_index& di)
+        {
+          using sema_rel::index;
+          table::names_iterator i (t.find (di.name ()));
+
+          if (i == t.names_end () || !i->nameable ().is_a<index> ())
+          {
+            cerr << "error: invalid changelog: index '" << di.name () <<
+              "' does not exist in table '" << t.name () << "'" << endl;
+            throw operation_failed ();
+          }
+
+          g.delete_edge (t, i->nameable (), *i);
+        }
+
+        virtual void
+        traverse (sema_rel::add_foreign_key& afk)
+        {
+          using sema_rel::foreign_key;
+
+          try
+          {
+            foreign_key& fk (g.new_node<foreign_key> (afk, t, g));
+            g.new_edge<unames> (t, fk, afk.name ());
+          }
+          catch (duplicate_name const&)
+          {
+            cerr << "error: invalid changelog: foreign key '" << afk.name () <<
+              "' already exists in table '" << t.name () << "'" << endl;
+            throw operation_failed ();
+          }
+        }
+
+        virtual void
+        traverse (sema_rel::drop_foreign_key& dfk)
+        {
+          using sema_rel::foreign_key;
+          table::names_iterator i (t.find (dfk.name ()));
+
+          if (i == t.names_end () || !i->nameable ().is_a<foreign_key> ())
+          {
+            cerr << "error: invalid changelog: foreign key '" << dfk.name () <<
+              "' does not exist in table '" << t.name () << "'" << endl;
+            throw operation_failed ();
+          }
+
+          g.delete_edge (t, i->nameable (), *i);
+        }
+
       protected:
         table& t;
         graph& g;
@@ -389,7 +705,7 @@ namespace relational
         //
         if (!mv.open)
         {
-          changeset& cs (diff (oldm, m, g));
+          changeset& cs (diff (oldm, m, *cl));
 
           if (!cs.names_empty ())
           {
@@ -432,7 +748,7 @@ namespace relational
           if (!mv.open)
           {
             model& old (patch (*last, cs, g));
-            changeset& cs (diff (old, m, g));
+            changeset& cs (diff (old, m, *cl));
 
             if (!cs.names_empty ())
             {
@@ -458,7 +774,14 @@ namespace relational
         if (last->version () <= mv.base)
           continue;
 
-        g.new_edge<contains_changeset> (*cl, g.new_node<changeset> (cs, g));
+        changeset& c (
+          g.new_node<changeset> (
+            cs,
+            cl->contains_changeset_empty ()
+            ? static_cast<qscope&> (*base) // Cannot be NULL.
+            : cl->contains_changeset_back ().changeset (),
+            g));
+        g.new_edge<contains_changeset> (*cl, c);
       }
 
       // If we still haven't found the new base model, then take the
@@ -473,7 +796,7 @@ namespace relational
 
       // Add a changeset for the current version.
       //
-      changeset& cs (diff (*last, m, g));
+      changeset& cs (diff (*last, m, *cl));
 
       if (!cs.names_empty ())
         g.new_edge<contains_changeset> (*cl, cs);
diff --git a/odb/semantics/relational/changelog.cxx b/odb/semantics/relational/changelog.cxx
index cd94494..fb304ca 100644
--- a/odb/semantics/relational/changelog.cxx
+++ b/odb/semantics/relational/changelog.cxx
@@ -3,6 +3,7 @@
 // license   : GNU GPL v3; see accompanying LICENSE file
 
 #include <vector>
+#include <sstream>
 
 #include <cutl/compiler/type-info.hxx>
 
@@ -10,6 +11,8 @@
 #include <odb/semantics/relational/model.hxx>
 #include <odb/semantics/relational/changeset.hxx>
 
+using namespace std;
+
 namespace semantics
 {
   namespace relational
@@ -26,10 +29,12 @@ namespace semantics
       if (p.attribute<unsigned int> ("version") != 1)
         throw parsing (p, "unsupported changelog format version");
 
-      // Get the changesets. Because they are stored in the reverse order,
-      // first save them to the temporary vector.
+      // Because things are stored in the reverse order, first save the
+      // changesets as XML chunks and then re-parse them in the reverse
+      // order. We have to do it this way so that we can do lookups along
+      // the alters edges.
       //
-      typedef std::vector<changeset*> changesets;
+      typedef vector<string> changesets;
       changesets cs;
 
       for (parser::event_type e (p.peek ());
@@ -39,22 +44,79 @@ namespace semantics
         if (p.qname () != xml::qname (xmlns, "changeset"))
           break; // Not our elements.
 
-        p.next ();
-        cs.push_back (&new_node<changeset> (p, *this));
-        p.next_expect (parser::end_element);
-      }
+        ostringstream os;
+        os.exceptions (ios_base::badbit | ios_base::failbit);
+        serializer s (os, "changeset", 0); // No pretty-printing.
+        size_t depth (0);
 
-      for (changesets::reverse_iterator i (cs.rbegin ()); i != cs.rend (); ++i)
-        new_edge<contains_changeset> (*this, **i);
+        do
+        {
+          switch (p.next ())
+          {
+          case parser::start_element:
+            {
+              s.start_element (p.qname ());
+
+              if (depth == 0)
+                s.namespace_decl (xmlns, "");
+
+              typedef parser::attribute_map_type attr_map;
+              attr_map const& am (p.attribute_map ());
+
+              for (attr_map::const_iterator i (am.begin ());
+                   i != am.end (); ++i)
+                s.attribute (i->first, i->second.value);
+
+              depth++;
+              break;
+            }
+          case parser::end_element:
+            {
+              depth--;
+              s.end_element ();
+              break;
+            }
+          case parser::characters:
+            {
+              s.characters (p.value ());
+              break;
+            }
+          default:
+            {
+              depth = 0;
+              break;
+            }
+          }
+        } while (depth != 0);
+
+        cs.push_back (os.str ());
+      }
 
       // Get the model.
       //
       p.next_expect (parser::start_element, xmlns, "model");
-
       model_type& m (new_node<model_type> (p, *this));
       new_edge<contains_model_type> (*this, m);
-
       p.next_expect (parser::end_element);
+
+      // Re-parse the changesets in reverse order.
+      //
+      qscope* base (&m);
+      for (changesets::reverse_iterator i (cs.rbegin ()); i != cs.rend (); ++i)
+      {
+        istringstream is (*i);
+        is.exceptions (ios_base::badbit | ios_base::failbit);
+        parser ip (is, p.input_name ());
+
+        ip.next_expect (parser::start_element, xmlns, "changeset");
+
+        changeset& c (new_node<changeset> (ip, *base, *this));
+        new_edge<contains_changeset> (*this, c);
+        base = &c;
+
+        ip.next_expect (parser::end_element);
+      }
+
       p.next_expect (parser::end_element);
     }
 
diff --git a/odb/semantics/relational/changeset.cxx b/odb/semantics/relational/changeset.cxx
index 8004844..fd5a17f 100644
--- a/odb/semantics/relational/changeset.cxx
+++ b/odb/semantics/relational/changeset.cxx
@@ -11,15 +11,15 @@ namespace semantics
   namespace relational
   {
     changeset::
-    changeset (changeset const& c, graph& g)
-      : qscope (c, g),
-        version_ (c.version_)
+    changeset (changeset const& c, qscope& b, graph& g)
+        : qscope (c, &b, g),
+          version_ (c.version_)
     {
     }
 
     changeset::
-    changeset (xml::parser& p, graph& g)
-        : qscope (p, g),
+    changeset (xml::parser& p, qscope& b, graph& g)
+        : qscope (p, &b, g),
           version_ (p.attribute<version_type> ("version"))
     {
     }
diff --git a/odb/semantics/relational/changeset.hxx b/odb/semantics/relational/changeset.hxx
index 575eb7b..76fd683 100644
--- a/odb/semantics/relational/changeset.hxx
+++ b/odb/semantics/relational/changeset.hxx
@@ -21,8 +21,8 @@ namespace semantics
 
     public:
       changeset (version_type v): version_ (v) {}
-      changeset (changeset const&, graph&);
-      changeset (xml::parser&, graph&);
+      changeset (changeset const&, qscope& base, graph&);
+      changeset (xml::parser&, qscope& base, graph&);
 
       virtual string
       kind () const {return "changeset";}
diff --git a/odb/semantics/relational/column.cxx b/odb/semantics/relational/column.cxx
index f90b94e..1a47ef7 100644
--- a/odb/semantics/relational/column.cxx
+++ b/odb/semantics/relational/column.cxx
@@ -104,20 +104,26 @@ namespace semantics
     // alter_column
     //
     alter_column::
-    alter_column (alter_column const& ac, uscope&, graph& g)
-        : unameable (ac, g),
-          null_altered_ (ac.null_altered_),
-          null_ (ac.null_)
+    alter_column (alter_column const& ac, uscope& s, graph& g)
+        : column (ac, s, g),
+          alters_ (0),
+          null_altered_ (ac.null_altered_)
     {
+      column* b (s.lookup<column, drop_column> (ac.name ()));
+      assert (b != 0);
+      g.new_edge<alters> (*this, *b);
     }
 
     alter_column::
-    alter_column (xml::parser& p, uscope&, graph& g)
-        : unameable (p, g),
-          null_altered_ (p.attribute_present ("null")),
-          null_ (null_altered_ ? p.attribute<bool> ("null") : false)
+    alter_column (xml::parser& p, uscope& s, graph& g)
+        : column (p, s, g),
+          alters_ (0),
+          null_altered_ (p.attribute_present ("null"))
     {
-      p.content (xml::parser::empty);
+      name_type n (p.attribute<name_type> ("name"));
+      column* b (s.lookup<column, drop_column> (n));
+      assert (b != 0);
+      g.new_edge<alters> (*this, *b);
     }
 
     alter_column& alter_column::
@@ -130,6 +136,9 @@ namespace semantics
     serialize (xml::serializer& s) const
     {
       s.start_element (xmlns, "alter-column");
+
+      // Here we override the standard column logic.
+      //
       unameable::serialize_attributes (s);
 
       if (null_altered_)
@@ -183,7 +192,7 @@ namespace semantics
           //
           {
             type_info ti (typeid (alter_column));
-            ti.add_base (typeid (unameable));
+            ti.add_base (typeid (column));
             insert (ti);
           }
         }
diff --git a/odb/semantics/relational/column.hxx b/odb/semantics/relational/column.hxx
index 7702a13..11a76e0 100644
--- a/odb/semantics/relational/column.hxx
+++ b/odb/semantics/relational/column.hxx
@@ -19,35 +19,32 @@ namespace semantics
       typedef std::vector<contains*> contained_list;
 
     public:
-      string const&
+      virtual string const&
       type () const {return type_;}
 
-      bool
+      virtual bool
       null () const {return null_;}
 
-      void
+      virtual void
       null (bool n) {null_ = n;}
 
-      string const&
+      virtual string const&
       default_ () const {return default__;}
 
-      void
+      virtual void
       default_ (string const& d) {default__ = d;}
 
-      string const&
+      virtual string const&
       options () const {return options_;}
 
-      void
+      virtual void
       options (string const& o) {options_ = o;}
 
     public:
       typedef relational::table table_type;
 
       table_type&
-      table () const
-      {
-        return dynamic_cast<table_type&> (scope ());
-      }
+      table () const {return dynamic_cast<table_type&> (scope ());}
 
       // Key containment.
       //
@@ -95,12 +92,13 @@ namespace semantics
       void
       serialize_attributes (xml::serializer&) const;
 
-    private:
+    protected:
       string type_;
       bool null_;
       string default__;
       string options_;
 
+    private:
       contained_list contained_;
     };
 
@@ -140,24 +138,34 @@ namespace semantics
       serialize (xml::serializer&) const;
     };
 
-    class alter_column: public unameable
+    class alter_column: public column
     {
     public:
+      virtual string const&
+      type () const {return base ().type ();}
+
       bool
       null_altered () const {return null_altered_;}
 
-      bool
-      null () const {return null_;}
+      virtual bool
+      null () const {return null_altered_ ? null_ : base ().null ();}
 
-      void
+      virtual void
       null (bool n) {null_ = n; null_altered_ = true;}
 
+      virtual string const&
+      default_ () const {return base ().default_ ();}
+
+      virtual string const&
+      options () const {return base ().options ();}
+
     public:
-      alter_column (string const& id)
-          : unameable (id), null_altered_ (false)
-      {
-      }
+      column&
+      base () const {return dynamic_cast<column&> (alters_->base ());}
 
+    public:
+      alter_column (string const& id)
+          : column (id, "", false), alters_ (0), null_altered_ (false) {}
       alter_column (alter_column const&, uscope&, graph&);
       alter_column (xml::parser&, uscope&, graph&);
 
@@ -173,9 +181,17 @@ namespace semantics
       virtual void
       serialize (xml::serializer&) const;
 
+      virtual void
+      add_edge_left (alters& a)
+      {
+        assert (alters_ == 0);
+        alters_ = &a;
+      }
+
     private:
+      alters* alters_;
+
       bool null_altered_;
-      bool null_;
     };
   }
 }
diff --git a/odb/semantics/relational/elements.cxx b/odb/semantics/relational/elements.cxx
index e14bc00..d83bff7 100644
--- a/odb/semantics/relational/elements.cxx
+++ b/odb/semantics/relational/elements.cxx
@@ -45,23 +45,36 @@ namespace semantics
       {
         typename names_list::iterator i;
 
-        // We want the order to be columns first, then the primary key,
-        // and then the foreign keys.
+        // We want the order to be add/alter columns first, then the
+        // primary key, then other keys, and finnally drop columns.
         //
-        if (n.is_a<column> ())
+        if (n.is_a<column> () ||
+            n.is_a<add_column> () ||
+            n.is_a<alter_column> ())
+        {
           i = names_.insert (first_key_, &e);
-        else
+        }
+        else if (!n.is_a<drop_column> ())
         {
           if (n.is_a<primary_key> ())
-            first_key_ = i = names_.insert (first_key_, &e);
+            first_key_ = i = names_.insert (
+              first_key_ != names_.end () ? first_key_ : first_drop_column_,
+              &e);
           else
           {
-            i = names_.insert (names_.end (), &e);
+            i = names_.insert (first_drop_column_, &e);
 
             if (first_key_ == names_.end ())
               first_key_ = i;
           }
         }
+        else
+        {
+          i = names_.insert (names_.end (), &e);
+
+          if (first_drop_column_ == names_.end ())
+            first_drop_column_ = i;
+        }
 
         names_map_[name] = i;
         iterator_map_[&e] = i;
@@ -83,6 +96,11 @@ namespace semantics
       if (first_key_ == i->second)
         first_key_++;
 
+      // The same for the first drop column.
+      //
+      if (first_drop_column_ == i->second)
+        first_drop_column_++;
+
       names_.erase (i->second);
       names_map_.erase (e.name ());
       iterator_map_.erase (i);
@@ -106,6 +124,14 @@ namespace semantics
           //
           insert (type_info (typeid (edge)));
 
+          // alters
+          //
+          {
+            type_info ti (typeid (alters));
+            ti.add_base (typeid (edge));
+            insert (ti);
+          }
+
           // names
           //
           {
diff --git a/odb/semantics/relational/elements.hxx b/odb/semantics/relational/elements.hxx
index 381d7a8..11e7ea8 100644
--- a/odb/semantics/relational/elements.hxx
+++ b/odb/semantics/relational/elements.hxx
@@ -93,9 +93,57 @@ namespace semantics
       //
     public:
       void
-      add_edge_right (edge&)
+      add_edge_right (edge&) {}
+
+      void
+      remove_edge_right (edge&) {}
+    };
+
+    //
+    //
+    class alters: public edge
+    {
+    public:
+      node&
+      base () const {return *base_;}
+
+      node&
+      modifier () const {return *modifier_;}
+
+    public:
+      alters () : base_ (0), modifier_ (0) {}
+
+      void
+      set_left_node (node& m)
+      {
+        assert (modifier_ == 0);
+        modifier_ = &m;
+      }
+
+      void
+      set_right_node (node& b)
       {
+        assert (base_ == 0);
+        base_ = &b;
       }
+
+      void
+      clear_left_node (node& m)
+      {
+        assert (modifier_ == &m);
+        modifier_ = 0;
+      }
+
+      void
+      clear_right_node (node& b)
+      {
+        assert (base_ == &b);
+        base_ = 0;
+      }
+
+    protected:
+      node* base_;
+      node* modifier_;
     };
 
     //
@@ -224,6 +272,7 @@ namespace semantics
       }
 
       using node::add_edge_right;
+      using node::remove_edge_right;
 
     protected:
       nameable (nameable const&, graph& g);
@@ -319,7 +368,7 @@ namespace semantics
         return names_.empty ();
       }
 
-      // Find.
+      // Find (this scope only).
       //
       template <typename T>
       T*
@@ -337,30 +386,64 @@ namespace semantics
       names_const_iterator
       find (names_type const&) const;
 
+      // Lookup in this and all altered scopes until we find what we are
+      // looking for or hit a stop node of type S (e.g., drop_*).
+      //
+      template <typename T, typename S>
+      T*
+      lookup (name_type const&);
+
+    public:
+      scope*
+      base () const
+      {
+        return alters_ != 0 ? &dynamic_cast<scope&> (alters_->base ()) : 0;
+      }
+
     public:
-      scope (): first_key_ (names_.end ()) {}
+      scope ()
+          : first_key_ (names_.end ()),
+            first_drop_column_ (names_.end ()),
+            alters_ (0) {}
 
       // Virtual because we call it via scope interface (e.g., in copy).
       //
       virtual void
+      add_edge_left (alters& a)
+      {
+        assert (alters_ == 0);
+        alters_ = &a;
+      }
+
+      virtual void
+      remove_edge_left (alters& a)
+      {
+        assert (alters_ == &a);
+        alters_ = 0;
+      }
+
+      virtual void
       add_edge_left (names_type&);
 
       virtual void
       remove_edge_left (names_type&);
 
     protected:
-      scope (scope const&, graph&);
-      scope (xml::parser&, graph&);
+      scope (scope const&, scope* base, graph&);
+      scope (xml::parser&, scope* base, graph&);
 
       void
       serialize_content (xml::serializer&) const;
 
-    private:
+    protected:
       names_list names_;
       names_map names_map_;
       names_iterator_map iterator_map_;
 
       typename names_list::iterator first_key_;
+      typename names_list::iterator first_drop_column_;
+
+      alters* alters_;
     };
 
     template <>
diff --git a/odb/semantics/relational/elements.txx b/odb/semantics/relational/elements.txx
index e1fd6d5..725fc3f 100644
--- a/odb/semantics/relational/elements.txx
+++ b/odb/semantics/relational/elements.txx
@@ -54,6 +54,23 @@ namespace semantics
     //
 
     template <typename N>
+    template <typename T, typename S>
+    T* scope<N>::
+    lookup (name_type const& name)
+    {
+      if (T* r = find<T> (name))
+        return r;
+
+      if (scope* b = base ())
+      {
+        if (find<S> (name) == 0)
+          return b->lookup<T, S> (name);
+      }
+
+      return 0;
+    }
+
+    template <typename N>
     template <typename T>
     T* scope<N>::
     find (name_type const& name)
@@ -106,9 +123,16 @@ namespace semantics
 
     template <typename N>
     scope<N>::
-    scope (scope const& s, graph& g)
-        : first_key_ (names_.end ())
+    scope (scope const& s, scope* base, graph& g)
+        : first_key_ (names_.end ()),
+          first_drop_column_ (names_.end ()),
+          alters_ (0)
     {
+      // Set the alters edge for lookup.
+      //
+      if (base != 0)
+        g.new_edge<alters> (*this, *base);
+
       for (names_const_iterator i (s.names_begin ());
            i != s.names_end (); ++i)
       {
@@ -119,9 +143,16 @@ namespace semantics
 
     template <typename N>
     scope<N>::
-    scope (xml::parser& p, graph& g)
-        : first_key_ (names_.end ())
+    scope (xml::parser& p, scope* base, graph& g)
+        : first_key_ (names_.end ()),
+          first_drop_column_ (names_.end ()),
+          alters_ (0)
     {
+      // Set the alters edge for lookup.
+      //
+      if (base != 0)
+        g.new_edge<alters> (*this, *base);
+
       using namespace xml;
       p.content (parser::complex);
 
diff --git a/odb/semantics/relational/foreign-key.cxx b/odb/semantics/relational/foreign-key.cxx
index 7ef88a6..0407858 100644
--- a/odb/semantics/relational/foreign-key.cxx
+++ b/odb/semantics/relational/foreign-key.cxx
@@ -89,11 +89,9 @@ namespace semantics
       return g.new_node<foreign_key> (*this, s, g);
     }
 
-
     void foreign_key::
-    serialize (xml::serializer& s) const
+    serialize_attributes (xml::serializer& s) const
     {
-      s.start_element (xmlns, "foreign-key");
       key::serialize_attributes (s);
 
       if (deferred ())
@@ -101,7 +99,11 @@ namespace semantics
 
       if (on_delete () != no_action)
         s.attribute ("on-delete", on_delete ());
+    }
 
+    void foreign_key::
+    serialize_content (xml::serializer& s) const
+    {
       key::serialize_content (s);
 
       // Referenced columns.
@@ -118,9 +120,57 @@ namespace semantics
       }
 
       s.end_element (); // references
+    }
+
+    void foreign_key::
+    serialize (xml::serializer& s) const
+    {
+      s.start_element (xmlns, "foreign-key");
+      serialize_attributes (s);
+      serialize_content (s);
       s.end_element (); // foreign-key
     }
 
+    // add_foreign_key
+    //
+    add_foreign_key& add_foreign_key::
+    clone (uscope& s, graph& g) const
+    {
+      return g.new_node<add_foreign_key> (*this, s, g);
+    }
+
+    void add_foreign_key::
+    serialize (xml::serializer& s) const
+    {
+      s.start_element (xmlns, "add-foreign-key");
+      foreign_key::serialize_attributes (s);
+      foreign_key::serialize_content (s);
+      s.end_element ();
+    }
+
+    // drop_foreign_key
+    //
+    drop_foreign_key::
+    drop_foreign_key (xml::parser& p, uscope&, graph& g)
+        : unameable (p, g)
+    {
+      p.content (xml::parser::empty);
+    }
+
+    drop_foreign_key& drop_foreign_key::
+    clone (uscope& s, graph& g) const
+    {
+      return g.new_node<drop_foreign_key> (*this, s, g);
+    }
+
+    void drop_foreign_key::
+    serialize (xml::serializer& s) const
+    {
+      s.start_element (xmlns, "drop-foreign-key");
+      unameable::serialize_attributes (s);
+      s.end_element ();
+    }
+
     // type info
     //
     namespace
@@ -129,16 +179,37 @@ namespace semantics
       {
         init ()
         {
-          unameable::parser_map_["foreign-key"] =
-            &unameable::parser_impl<foreign_key>;
+          unameable::parser_map& m (unameable::parser_map_);
+
+          m["foreign-key"] = &unameable::parser_impl<foreign_key>;
+          m["add-foreign-key"] = &unameable::parser_impl<add_foreign_key>;
+          m["drop-foreign-key"] = &unameable::parser_impl<drop_foreign_key>;
 
           using compiler::type_info;
 
+          // foreign_key
+          //
           {
             type_info ti (typeid (foreign_key));
             ti.add_base (typeid (key));
             insert (ti);
           }
+
+          // add_foreign_key
+          //
+          {
+            type_info ti (typeid (add_foreign_key));
+            ti.add_base (typeid (foreign_key));
+            insert (ti);
+          }
+
+          // drop_foreign_key
+          //
+          {
+            type_info ti (typeid (drop_foreign_key));
+            ti.add_base (typeid (unameable));
+            insert (ti);
+          }
         }
       } init_;
     }
diff --git a/odb/semantics/relational/foreign-key.hxx b/odb/semantics/relational/foreign-key.hxx
index 5d551fe..50a3fae 100644
--- a/odb/semantics/relational/foreign-key.hxx
+++ b/odb/semantics/relational/foreign-key.hxx
@@ -83,6 +83,13 @@ namespace semantics
       virtual void
       serialize (xml::serializer&) const;
 
+    protected:
+      void
+      serialize_attributes (xml::serializer&) const;
+
+      void
+      serialize_content (xml::serializer&) const;
+
     private:
       qname referenced_table_;
       columns referenced_columns_;
@@ -95,6 +102,47 @@ namespace semantics
 
     std::istream&
     operator>> (std::istream&, foreign_key::action_type&);
+
+    class add_foreign_key: public foreign_key
+    {
+    public:
+      add_foreign_key (string const& id,
+                       qname const& rt,
+                       bool d,
+                       action_type od = no_action)
+          : foreign_key (id, rt, d, od) {}
+      add_foreign_key (foreign_key const& fk, uscope& s, graph& g)
+          : foreign_key (fk, s, g) {}
+      add_foreign_key (xml::parser& p, uscope& s, graph& g)
+          : foreign_key (p, s, g) {}
+
+      virtual add_foreign_key&
+      clone (uscope&, graph&) const;
+
+      virtual string
+      kind () const {return "add foreign key";}
+
+      virtual void
+      serialize (xml::serializer&) const;
+    };
+
+    class drop_foreign_key: public unameable
+    {
+    public:
+      drop_foreign_key (string const& id): unameable (id) {}
+      drop_foreign_key (drop_foreign_key const& dfk, uscope&, graph& g)
+          : unameable (dfk, g) {}
+      drop_foreign_key (xml::parser&, uscope&, graph&);
+
+      virtual drop_foreign_key&
+      clone (uscope&, graph&) const;
+
+      virtual string
+      kind () const {return "drop foreign key";}
+
+      virtual void
+      serialize (xml::serializer&) const;
+    };
   }
 }
 
diff --git a/odb/semantics/relational/index.cxx b/odb/semantics/relational/index.cxx
index 5ff1a26..b38c6e4 100644
--- a/odb/semantics/relational/index.cxx
+++ b/odb/semantics/relational/index.cxx
@@ -10,6 +10,8 @@ namespace semantics
 {
   namespace relational
   {
+    // index
+    //
     index::
     index (index const& i, uscope& s, graph& g)
         : key (i, s, g),
@@ -35,9 +37,8 @@ namespace semantics
     }
 
     void index::
-    serialize (xml::serializer& s) const
+    serialize_attributes (xml::serializer& s) const
     {
-      s.start_element (xmlns, "index");
       key::serialize_attributes (s);
 
       if (!type ().empty ())
@@ -48,11 +49,57 @@ namespace semantics
 
       if (!options ().empty ())
         s.attribute ("options", options ());
+    }
 
+    void index::
+    serialize (xml::serializer& s) const
+    {
+      s.start_element (xmlns, "index");
+      serialize_attributes (s);
       key::serialize_content (s);
       s.end_element ();
     }
 
+    // add_index
+    //
+    add_index& add_index::
+    clone (uscope& s, graph& g) const
+    {
+      return g.new_node<add_index> (*this, s, g);
+    }
+
+    void add_index::
+    serialize (xml::serializer& s) const
+    {
+      s.start_element (xmlns, "add-index");
+      index::serialize_attributes (s);
+      index::serialize_content (s);
+      s.end_element ();
+    }
+
+    // drop_index
+    //
+    drop_index::
+    drop_index (xml::parser& p, uscope&, graph& g)
+        : unameable (p, g)
+    {
+      p.content (xml::parser::empty);
+    }
+
+    drop_index& drop_index::
+    clone (uscope& s, graph& g) const
+    {
+      return g.new_node<drop_index> (*this, s, g);
+    }
+
+    void drop_index::
+    serialize (xml::serializer& s) const
+    {
+      s.start_element (xmlns, "drop-index");
+      unameable::serialize_attributes (s);
+      s.end_element ();
+    }
+
     // type info
     //
     namespace
@@ -61,15 +108,37 @@ namespace semantics
       {
         init ()
         {
-          unameable::parser_map_["index"] = &unameable::parser_impl<index>;
+          unameable::parser_map& m (unameable::parser_map_);
+
+          m["index"] = &unameable::parser_impl<index>;
+          m["add-index"] = &unameable::parser_impl<add_index>;
+          m["drop-index"] = &unameable::parser_impl<drop_index>;
 
           using compiler::type_info;
 
+          // index
+          //
           {
             type_info ti (typeid (index));
             ti.add_base (typeid (key));
             insert (ti);
           }
+
+          // add_index
+          //
+          {
+            type_info ti (typeid (add_index));
+            ti.add_base (typeid (index));
+            insert (ti);
+          }
+
+          // drop_index
+          //
+          {
+            type_info ti (typeid (drop_index));
+            ti.add_base (typeid (unameable));
+            insert (ti);
+          }
         }
       } init_;
     }
diff --git a/odb/semantics/relational/index.hxx b/odb/semantics/relational/index.hxx
index 621f36a..500c341 100644
--- a/odb/semantics/relational/index.hxx
+++ b/odb/semantics/relational/index.hxx
@@ -31,10 +31,7 @@ namespace semantics
              string const& t = string (),
              string const& m = string (),
              string const& o = string ())
-          : key (id), type_ (t), method_ (m), options_ (o)
-      {
-      }
-
+          : key (id), type_ (t), method_ (m), options_ (o) {}
       index (index const&, uscope&, graph&);
       index (xml::parser&, uscope&, graph&);
 
@@ -50,11 +47,54 @@ namespace semantics
       virtual void
       serialize (xml::serializer&) const;
 
+    protected:
+      void
+      serialize_attributes (xml::serializer&) const;
+
     private:
       string type_;    // E.g., "UNIQUE", etc.
       string method_;  // E.g., "BTREE", etc.
       string options_; // Database-specific index options.
     };
+
+    class add_index: public index
+    {
+    public:
+      add_index (string const& id,
+                 string const& t = string (),
+                 string const& m = string (),
+                 string const& o = string ())
+          : index (id, t, m, o) {}
+      add_index (index const& i, uscope& s, graph& g): index (i, s, g) {}
+      add_index (xml::parser& p, uscope& s, graph& g): index (p, s, g) {}
+
+      virtual add_index&
+      clone (uscope&, graph&) const;
+
+      virtual string
+      kind () const {return "add index";}
+
+      virtual void
+      serialize (xml::serializer&) const;
+    };
+
+    class drop_index: public unameable
+    {
+    public:
+      drop_index (string const& id): unameable (id) {}
+      drop_index (drop_index const& di, uscope&, graph& g)
+          : unameable (di, g) {}
+      drop_index (xml::parser&, uscope&, graph&);
+
+      virtual drop_index&
+      clone (uscope&, graph&) const;
+
+      virtual string
+      kind () const {return "drop index";}
+
+      virtual void
+      serialize (xml::serializer&) const;
+    };
   }
 }
 
diff --git a/odb/semantics/relational/key.cxx b/odb/semantics/relational/key.cxx
index e27253c..dc0fbe0 100644
--- a/odb/semantics/relational/key.cxx
+++ b/odb/semantics/relational/key.cxx
@@ -18,7 +18,7 @@ namespace semantics
       for (contains_iterator i (k.contains_begin ());
            i != k.contains_end (); ++i)
       {
-        column* c (s.find<column> (i->column ().name ()));
+        column* c (s.lookup<column, drop_column> (i->column ().name ()));
         assert (c != 0);
         g.new_edge<contains> (*this, *c, i->options ());
       }
@@ -42,7 +42,7 @@ namespace semantics
         p.content (parser::empty);
 
         uname n (p.attribute<uname> ("name"));
-        column* c (s.find<column> (n));
+        column* c (s.lookup<column, drop_column> (n));
         if (c == 0)
           throw parsing (p, "invalid column name in the 'name' attribute");
 
diff --git a/odb/semantics/relational/key.hxx b/odb/semantics/relational/key.hxx
index 8d64993..184433e 100644
--- a/odb/semantics/relational/key.hxx
+++ b/odb/semantics/relational/key.hxx
@@ -6,6 +6,7 @@
 #define ODB_SEMANTICS_RELATIONAL_KEY_HXX
 
 #include <odb/semantics/relational/elements.hxx>
+#include <odb/semantics/relational/table.hxx>
 
 namespace semantics
 {
@@ -55,6 +56,8 @@ namespace semantics
       typedef std::vector<contains*> contains_list;
 
     public:
+      typedef contains_list::size_type contains_size_type;
+
       typedef
       pointer_iterator<contains_list::const_iterator>
       contains_iterator;
@@ -65,9 +68,18 @@ namespace semantics
       contains_iterator
       contains_end () const {return contains_.end ();}
 
-      contains_list::size_type
+      contains_size_type
       contains_size () const {return contains_.size ();}
 
+      contains&
+      contains_at (contains_size_type i) const {return *contains_[i];}
+
+    public:
+      typedef relational::table table_type;
+
+      table_type&
+      table () const {return dynamic_cast<table_type&> (scope ());}
+
     public:
       key (std::string const& id): unameable (id) {}
 
diff --git a/odb/semantics/relational/model.cxx b/odb/semantics/relational/model.cxx
index 6515591..678debe 100644
--- a/odb/semantics/relational/model.cxx
+++ b/odb/semantics/relational/model.cxx
@@ -12,14 +12,14 @@ namespace semantics
   {
     model::
     model (model const& m, graph& g)
-        : qscope (m, g),
+        : qscope (m, 0, g),
           version_ (m.version_)
     {
     }
 
     model::
     model (xml::parser& p, graph& g)
-        : qscope (p, g),
+        : qscope (p, 0, g),
           version_ (p.attribute<version_type> ("version"))
     {
     }
diff --git a/odb/semantics/relational/name.hxx b/odb/semantics/relational/name.hxx
index 18c7509..06794be 100644
--- a/odb/semantics/relational/name.hxx
+++ b/odb/semantics/relational/name.hxx
@@ -125,6 +125,18 @@ namespace semantics
 
     public:
       friend bool
+      operator== (qname const& x, qname const& y)
+      {
+        return x.components_ == y.components_;
+      }
+
+      friend bool
+      operator!= (qname const& x, qname const& y)
+      {
+        return x.components_ != y.components_;
+      }
+
+      friend bool
       operator< (qname const& x, qname const& y)
       {
         return x.components_ < y.components_;
diff --git a/odb/semantics/relational/table.cxx b/odb/semantics/relational/table.cxx
index 682196c..17265bd 100644
--- a/odb/semantics/relational/table.cxx
+++ b/odb/semantics/relational/table.cxx
@@ -13,14 +13,20 @@ namespace semantics
     // table
     //
     table::
-    table (table const& t, qscope&, graph& g)
-        : qnameable (t, g), uscope (t, g)
+    table (table const& t, qscope& s, graph& g, bool b)
+        : qnameable (t, g),
+          uscope (t, (b ? s.lookup<table, drop_table> (t.name ()) : 0), g)
     {
     }
 
     table::
-    table (xml::parser& p, qscope&, graph& g)
-        : qnameable (p, g), uscope (p, g)
+    table (xml::parser& p, qscope& s, graph& g, bool b)
+        : qnameable (p, g),
+          uscope (
+            p,
+            (b ? s.lookup<table, drop_table> (
+              p.attribute<qnameable::name_type> ("name")) : 0),
+            g)
     {
     }
 
@@ -81,18 +87,6 @@ namespace semantics
 
     // alter_table
     //
-    alter_table::
-    alter_table (alter_table const& t, qscope&, graph& g)
-        : qnameable (t, g), uscope (t, g)
-    {
-    }
-
-    alter_table::
-    alter_table (xml::parser& p, qscope&, graph& g)
-        : qnameable (p, g), uscope (p, g)
-    {
-    }
-
     alter_table& alter_table::
     clone (qscope& s, graph& g) const
     {
@@ -103,8 +97,8 @@ namespace semantics
     serialize (xml::serializer& s) const
     {
       s.start_element (xmlns, "alter-table");
-      qnameable::serialize_attributes (s);
-      uscope::serialize_content (s);
+      table::serialize_attributes (s);
+      table::serialize_content (s);
       s.end_element ();
     }
 
@@ -154,8 +148,7 @@ namespace semantics
           //
           {
             type_info ti (typeid (alter_table));
-            ti.add_base (typeid (qnameable));
-            ti.add_base (typeid (uscope));
+            ti.add_base (typeid (table));
             insert (ti);
           }
         }
diff --git a/odb/semantics/relational/table.hxx b/odb/semantics/relational/table.hxx
index effd552..ae4c96c 100644
--- a/odb/semantics/relational/table.hxx
+++ b/odb/semantics/relational/table.hxx
@@ -15,8 +15,8 @@ namespace semantics
     {
     public:
       table (string const& id): qnameable (id) {}
-      table (table const&, qscope&, graph&);
-      table (xml::parser&, qscope&, graph&);
+      table (table const&, qscope&, graph&, bool base = false);
+      table (xml::parser&, qscope&, graph&, bool base = false);
 
       virtual table&
       clone (qscope&, graph&) const;
@@ -66,12 +66,14 @@ namespace semantics
       serialize (xml::serializer&) const;
     };
 
-    class alter_table: public qnameable, public uscope
+    class alter_table: public table
     {
     public:
-      alter_table (string const& id): qnameable (id) {}
-      alter_table (alter_table const&, qscope&, graph&);
-      alter_table (xml::parser&, qscope&, graph&);
+      alter_table (string const& id): table (id) {}
+      alter_table (alter_table const& at, qscope& s, graph& g)
+          : table (at, s, g, true) {}
+      alter_table (xml::parser& p, qscope& s, graph& g)
+          : table (p, s, g, true) {}
 
       virtual alter_table&
       clone (qscope&, graph&) const;
@@ -81,10 +83,6 @@ namespace semantics
 
       virtual void
       serialize (xml::serializer&) const;
-
-      // Resolve ambiguity.
-      //
-      using qnameable::scope;
     };
   }
 }
diff --git a/odb/traversal/relational/foreign-key.hxx b/odb/traversal/relational/foreign-key.hxx
index d80df26..1dc54e9 100644
--- a/odb/traversal/relational/foreign-key.hxx
+++ b/odb/traversal/relational/foreign-key.hxx
@@ -13,6 +13,9 @@ namespace traversal
   namespace relational
   {
     struct foreign_key: key_template<semantics::relational::foreign_key> {};
+    struct add_foreign_key:
+      key_template<semantics::relational::add_foreign_key> {};
+    struct drop_foreign_key: node<semantics::relational::drop_foreign_key> {};
   }
 }
 
diff --git a/odb/traversal/relational/index.hxx b/odb/traversal/relational/index.hxx
index f45dda7..7426ab4 100644
--- a/odb/traversal/relational/index.hxx
+++ b/odb/traversal/relational/index.hxx
@@ -13,6 +13,8 @@ namespace traversal
   namespace relational
   {
     struct index: key_template<semantics::relational::index> {};
+    struct add_index: key_template<semantics::relational::add_index> {};
+    struct drop_index: node<semantics::relational::drop_index> {};
   }
 }
 
-- 
cgit v1.1