diff --git a/brmbar3/SQL b/brmbar3/SQL
index a61dba8..04667f4 100644
--- a/brmbar3/SQL
+++ b/brmbar3/SQL
@@ -1,11 +1,11 @@
-CREATE SEQUENCE currencies_id_seq START WITH 1 INCREMENT BY 1;
+CREATE SEQUENCE currencies_id_seq START WITH 2 INCREMENT BY 1;
 CREATE TABLE currencies (
 	id INTEGER PRIMARY KEY NOT NULL DEFAULT NEXTVAL('currencies_id_seq'::regclass),
 	name VARCHAR(128) NOT NULL,
 	UNIQUE(name)
 );
 -- Some code depends on the primary physical currency to have id 1.
-INSERT INTO currencies (name) VALUES ('Kč');
+INSERT INTO currencies (id, name) VALUES (1, 'Kč');
 
 CREATE TYPE exchange_rate_direction AS ENUM ('source_to_target', 'target_to_source');
 CREATE TABLE exchange_rates (
diff --git a/brmbar3/SQL-for-RO-access.sql b/brmbar3/SQL-for-RO-access.sql
new file mode 100644
index 0000000..b8c7291
--- /dev/null
+++ b/brmbar3/SQL-for-RO-access.sql
@@ -0,0 +1,57 @@
+CREATE OR REPLACE FUNCTION accounts_id_seq_value()
+RETURNS bigint
+LANGUAGE plpgsql
+SECURITY DEFINER
+AS $$
+DECLARE
+    result bigint;
+BEGIN
+    SELECT last_value FROM accounts_id_seq
+    INTO result;
+    RETURN result;
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION transactions_id_seq_value()
+RETURNS bigint
+LANGUAGE plpgsql
+SECURITY DEFINER
+AS $$
+DECLARE
+    result bigint;
+BEGIN
+    SELECT last_value FROM transactions_id_seq
+    INTO result;
+    RETURN result;
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION transaction_splits_id_seq_value()
+RETURNS bigint
+LANGUAGE plpgsql
+SECURITY DEFINER
+AS $$
+DECLARE
+    result bigint;
+BEGIN
+    SELECT last_value FROM transaction_splits_id_seq
+    INTO result;
+    RETURN result;
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION currencies_id_seq_value()
+RETURNS bigint
+LANGUAGE plpgsql
+SECURITY DEFINER
+AS $$
+DECLARE
+    result bigint;
+BEGIN
+    SELECT last_value FROM currencies_id_seq
+    INTO result;
+    RETURN result;
+END;
+$$;
+
+
diff --git a/brmbar3/SQL-schema-v001.sql b/brmbar3/SQL-schema-v001.sql
new file mode 100644
index 0000000..44b9693
--- /dev/null
+++ b/brmbar3/SQL-schema-v001.sql
@@ -0,0 +1,59 @@
+--RESET search_path;
+SELECT pg_catalog.set_config('search_path', '', false);
+-- intoduce implementation schema
+CREATE SCHEMA IF NOT EXISTS brmbar_implementation;
+-- version table (with initialization)
+CREATE TABLE IF NOT EXISTS brmbar_implementation.brmbar_schema (
+	ver INTEGER NOT NULL
+);
+DO $$
+DECLARE v INTEGER;
+BEGIN
+	SELECT ver FROM brmbar_implementation.brmbar_schema INTO v;
+	IF v IS NULL THEN
+		INSERT INTO brmbar_implementation.brmbar_schema (ver) VALUES (1);
+	END IF;
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION brmbar_implementation.has_exact_schema_version(
+	IN i_ver INTEGER NOT NULL
+) RETURNS INTEGER
+VOLATILE  NOT LEAKPROOF  LANGUAGE plpgsql AS $$
+DECLARE
+	v_ver INTEGER;
+BEGIN
+	SELECT ver INTO STRICT v_ver FROM brmbar_implementation.brmbar_schema;
+	IF v_ver IS NULL or v_ver <> i_ver THEN
+		RAISE EXCEPTION 'Invalid brmbar schema version';
+	END IF;
+	RETURN v_ver;
+/*
+EXCEPTION
+	WHEN NO_DATA_FOUND THEN
+		RAISE EXCEPTION 'PID % not found';
+	WHEN TOO_MANY_ROWS THEN
+		RAISE EXCEPTION 'PID % not unique';
+*/
+END;
+$$;
+
+CREATE OR REPLACE FUNCTION brmbar_implementation.upgrade_schema_version_to(
+	IN i_ver INTEGER NOT NULL
+) RETURNS INTEGER
+VOLATILE  NOT LEAKPROOF  LANGUAGE plpgsql AS $$
+DECLARE
+	v_ver INTEGER;
+BEGIN
+	SELECT brmbar_implementation.has_exact_schema_version(i_ver) INTO v_ver;
+	IF v_ver + 1 = i_ver THEN
+		UPDATE brmbar_implementation.brmbar_schema SET ver = i_ver;
+	ELSE
+		RAISE EXCEPTION 'Invalid brmbar schema version';
+	END IF;
+	RETURN i_ver;
+END;
+$$;
+
+-- vim: set ft=plsql :
+
diff --git a/brmbar3/SQL-schema-v002.sql b/brmbar3/SQL-schema-v002.sql
new file mode 100644
index 0000000..bfb63fa
--- /dev/null
+++ b/brmbar3/SQL-schema-v002.sql
@@ -0,0 +1,61 @@
+--RESET search_path
+SELECT pg_catalog.set_config('search_path', '', false);
+
+--- upgrade schema
+DO $upgrade_block$
+DECLARE
+current_ver INTEGER;
+BEGIN
+
+-- confirm that we are upgrading from version 1
+SELECT brmbar_implementation.has_exact_schema_version(1) INTO current_ver;
+IF current_ver <> 1 THEN
+	RAISE EXCEPTION 'BrmBar schema version % cannot be upgraded to version 2.', current_ver;
+END IF;
+
+-- structural changes
+
+-- TRADING ACCOUNTS
+--START TRANSACTION ISOLATION LEVEL SERIALIZABLE;
+
+-- currency trading accounts - account type
+ALTER TYPE public.account_type ADD VALUE IF NOT EXISTS 'trading';
+
+-- constraint needed for foreign key in currencies table
+ALTER TABLE public.accounts ADD CONSTRAINT accounts_id_acctype_key UNIQUE(id, acctype);
+
+-- add columns to currencies to record the trading account associated with the currency
+ALTER TABLE public.currencies
+	ADD COLUMN IF NOT EXISTS trading_account integer,
+	ADD COLUMN IF NOT EXISTS trading_account_type account_type GENERATED ALWAYS AS ('trading'::public.account_type) STORED;
+
+-- make trading accounts (without making duplicates)
+INSERT INTO public.accounts ("name", "currency", acctype)
+SELECT
+	'Currency Trading Account: ' || c."name",
+	c.id,
+	'trading'::public.account_type
+FROM public.currencies AS c
+WHERE NOT EXISTS (
+	SELECT 1
+	FROM public.accounts a
+	WHERE a.currency = c.id AND a.acctype = 'trading'::public.account_type
+);
+
+
+-- record the trading account IDs in currencies table
+UPDATE public.currencies AS c SET (trading_account) = (SELECT a.id FROM public.accounts AS a WHERE a.currency = c.id AND c.acctype = 'trading'::public.account_type);
+
+-- foreign key to check the validity of currency trading account reference
+ALTER TABLE public.currencies
+	ADD CONSTRAINT currencies_trading_fkey FOREIGN KEY (trading_account, trading_account_type)
+		REFERENCES xaccounts(id,acctype) DEFERRABLE INITIALLY DEFERRED;
+
+--COMMIT AND CHAIN;
+
+SELECT brmbar_implementation.upgrade_schema_version_to(2) INTO current_ver;
+-- end of upgrade do block
+end
+$upgrade_block$;
+
+-- vim: set ft=plsql :
diff --git a/brmbar3/brmbar/Shop.py b/brmbar3/brmbar/Shop.py
index 6027084..5049fcc 100644
--- a/brmbar3/brmbar/Shop.py
+++ b/brmbar3/brmbar/Shop.py
@@ -219,14 +219,15 @@ class Shop:
         self.db.commit()
 
     def undo(self, oldtid):
-        description = self.db.execute_and_fetch("SELECT description FROM transactions WHERE id = %s", [oldtid])[0]
-        description = 'undo %d (%s)' % (oldtid, description)
+        #description = self.db.execute_and_fetch("SELECT description FROM transactions WHERE id = %s", [oldtid])[0]
+        #description = 'undo %d (%s)' % (oldtid, description)
 
-        transaction = self._transaction(description=description)
-        for split in self.db.execute_and_fetchall("SELECT id, side, account, amount, memo FROM transaction_splits WHERE transaction = %s", [oldtid]):
-            splitid, side, account, amount, memo = split
-            memo = 'undo %d (%s)' % (splitid, memo)
-            amount = -amount
-            self.db.execute("INSERT INTO transaction_splits (transaction, side, account, amount, memo) VALUES (%s, %s, %s, %s, %s)", [transaction, side, account, amount, memo])
+        #transaction = self._transaction(description=description)
+        #for split in self.db.execute_and_fetchall("SELECT id, side, account, amount, memo FROM transaction_splits WHERE transaction = %s", [oldtid]):
+        #    splitid, side, account, amount, memo = split
+        #    memo = 'undo %d (%s)' % (splitid, memo)
+        #    amount = -amount
+        #    self.db.execute("INSERT INTO transaction_splits (transaction, side, account, amount, memo) VALUES (%s, %s, %s, %s, %s)", [transaction, side, account, amount, memo])
+        transaction = self.db.execute_and_fetch("CALL undo_transaction(%s)",[oldtid])[0]
         self.db.commit()
         return transaction