diff --git a/openerp/workflow/instance.py b/openerp/workflow/instance.py
index befbd5970f7..223e90cca31 100644
--- a/openerp/workflow/instance.py
+++ b/openerp/workflow/instance.py
@@ -23,85 +23,111 @@ from openerp.workflow.helpers import Session
 from openerp.workflow.helpers import Record
 from openerp.workflow.workitem import WorkflowItem
 
-def create(session, record, workflow_id):
-    assert isinstance(session, Session)
-    assert isinstance(record, Record)
-    assert isinstance(workflow_id, (int, long))
+class WorkflowInstance(object):
+    def __init__(self, session, record, values):
+        assert isinstance(session, Session)
+        assert isinstance(record, Record)
+        self.session = session
+        self.record = record
 
-    cr = session.cr
-    cr.execute('insert into wkf_instance (res_type,res_id,uid,wkf_id) values (%s,%s,%s,%s) RETURNING id', (record.model, record.id, session.uid, workflow_id))
-    instance_id = cr.fetchone()[0]
-    cr.execute('select * from wkf_activity where flow_start=True and wkf_id=%s', (workflow_id,))
-    activities = cr.dictfetchall()
-    stack = []
-    WorkflowItem(session, record).create(activities, instance_id, stack)
-    update(session, record, instance_id)
-    return instance_id
+        if not values:
+            values = {}
+
+        assert isinstance(values, dict)
+        self.instance = values
+
+    @classmethod
+    def create(cls, session, record, workflow_id):
+        assert isinstance(session, Session)
+        assert isinstance(record, Record)
+        assert isinstance(workflow_id, (int, long))
+
+        cr = session.cr
+        cr.execute('insert into wkf_instance (res_type,res_id,uid,wkf_id) values (%s,%s,%s,%s) RETURNING id', (record.model, record.id, session.uid, workflow_id))
+        instance_id = cr.fetchone()[0]
+
+        cr.execute('select * from wkf_activity where flow_start=True and wkf_id=%s', (workflow_id,))
+        stack = []
+
+        activities = cr.dictfetchall()
+        for activity in activities:
+            WorkflowItem.create(session, record, activity, instance_id, stack)
+
+        cr.execute('SELECT * FROM wkf_instance WHERE id = %s', (instance_id,))
+        values = cr.dictfetchone()
+        wi = WorkflowInstance(session, record, values)
+        wi.update()
+
+        return wi
+
+    def delete(self):
+        self.session.cr.execute('delete from wkf_instance where res_id=%s and res_type=%s', (self.record.id, self.record.model))
+
+    def validate(self, signal, force_running=False):
+        assert isinstance(signal, basestring)
+        assert isinstance(force_running, bool)
+
+        cr = self.session.cr
+        cr.execute("select * from wkf_workitem where inst_id=%s", (self.instance['id'],))
+        stack = []
+        for work_item_values in cr.dictfetchall():
+            wi = WorkflowItem(self.session, self.record, work_item_values)
+            wi.process(signal=signal, force_running=force_running, stack=stack)
+            # An action is returned
+        self._update_end()
+        return stack and stack[0] or False
+
+    def update(self):
+        cr = self.session.cr
+
+        cr.execute("select * from wkf_workitem where inst_id=%s", (self.instance['id'],))
+        for work_item_values in cr.dictfetchall():
+            stack = []
+            WorkflowItem(self.session, self.record, work_item_values).process(stack=stack)
+        return self._update_end()
+
+    def _update_end(self):
+        cr = self.session.cr
+        instance_id = self.instance['id']
+        cr.execute('select wkf_id from wkf_instance where id=%s', (instance_id,))
+        wkf_id = cr.fetchone()[0]
+        cr.execute('select state,flow_stop from wkf_workitem w left join wkf_activity a on (a.id=w.act_id) where w.inst_id=%s', (instance_id,))
+        ok=True
+        for r in cr.fetchall():
+            if (r[0]<>'complete') or not r[1]:
+                ok=False
+                break
+        if ok:
+            cr.execute('select distinct a.name from wkf_activity a left join wkf_workitem w on (a.id=w.act_id) where w.inst_id=%s', (instance_id,))
+            act_names = cr.fetchall()
+            cr.execute("update wkf_instance set state='complete' where id=%s", (instance_id,))
+            cr.execute("update wkf_workitem set state='complete' where subflow_id=%s", (instance_id,))
+            cr.execute("select i.id,w.osv,i.res_id from wkf_instance i left join wkf w on (i.wkf_id=w.id) where i.id IN (select inst_id from wkf_workitem where subflow_id=%s)", (instance_id,))
+            for cur_instance_id, cur_model_name, cur_record_id in cr.fetchall():
+                cur_record = Record(cur_model_name, cur_record_id)
+                for act_name in act_names:
+                    WorkflowInstance(self.session, cur_record, {'id':cur_instance_id}).validate('subflow.{}'.format(act_name[0]))
+
+        return ok
+
+
+
+
+
+def create(session, record, workflow_id):
+    return WorkflowInstance(session, record).create(workflow_id)
 
 def delete(session, record):
-    assert isinstance(session, Session)
-    assert isinstance(record, Record)
-
-    session.cr.execute('delete from wkf_instance where res_id=%s and res_type=%s', (record.id, record.model))
+    return WorkflowInstance(session, record).delete()
 
 def validate(session, record, instance_id, signal, force_running=False):
-    assert isinstance(session, Session)
-    assert isinstance(record, Record)
-    assert isinstance(instance_id, (long, int))
-    assert isinstance(signal, basestring)
-    assert isinstance(force_running, bool)
-
-    cr = session.cr
-    cr.execute("select * from wkf_workitem where inst_id=%s", (instance_id,))
-    stack = []
-    wi = WorkflowItem(session, record)
-    for work_item in cr.dictfetchall():
-        # stack = []
-        wi.process(work_item, signal, force_running, stack=stack)
-        # An action is returned
-    _update_end(session, record, instance_id)
-    return stack and stack[0] or False
+    return WorkflowInstance(session, record).validate(instance_id, signal, force_running)
 
 def update(session, record, instance_id):
-    assert isinstance(session, Session)
-    assert isinstance(record, Record)
-    assert isinstance(instance_id, (long, int))
-
-    cr = session.cr
-    cr.execute("select * from wkf_workitem where inst_id=%s", (instance_id,))
-    wi = WorkflowItem(session, record)
-
-    for work_item in cr.dictfetchall():
-        stack = []
-        wi.process(work_item, stack=stack)
-    return _update_end(session, record, instance_id)
+    return WorkflowInstance(session, record).update(instance_id)
 
 def _update_end(session, record, instance_id):
-    assert isinstance(session, Session)
-    assert isinstance(record, Record)
-    assert isinstance(instance_id, (long, int))
-
-    cr = session.cr
-    cr.execute('select wkf_id from wkf_instance where id=%s', (instance_id,))
-    wkf_id = cr.fetchone()[0]
-    cr.execute('select state,flow_stop from wkf_workitem w left join wkf_activity a on (a.id=w.act_id) where w.inst_id=%s', (instance_id,))
-    ok=True
-    for r in cr.fetchall():
-        if (r[0]<>'complete') or not r[1]:
-            ok=False
-            break
-    if ok:
-        cr.execute('select distinct a.name from wkf_activity a left join wkf_workitem w on (a.id=w.act_id) where w.inst_id=%s', (instance_id,))
-        act_names = cr.fetchall()
-        cr.execute("update wkf_instance set state='complete' where id=%s", (instance_id,))
-        cr.execute("update wkf_workitem set state='complete' where subflow_id=%s", (instance_id,))
-        cr.execute("select i.id,w.osv,i.res_id from wkf_instance i left join wkf w on (i.wkf_id=w.id) where i.id IN (select inst_id from wkf_workitem where subflow_id=%s)", (instance_id,))
-        for cur_instance_id, cur_model_name, cur_record_id in cr.fetchall():
-            cur_record = Record(cur_model_name, cur_record_id)
-            for act_name in act_names:
-                validate(session, cur_record, cur_instance_id, 'subflow.%s' % act_name[0])
-
-    return ok
+    return WorkflowInstance(session, record)._update_end(instance_id)
 
 
 # vim:expandtab:smartindent:tabstop=4:softtabstop=4:shiftwidth=4:
diff --git a/openerp/workflow/service.py b/openerp/workflow/service.py
index 08c0f61a7a2..cf8a5449b07 100644
--- a/openerp/workflow/service.py
+++ b/openerp/workflow/service.py
@@ -21,7 +21,8 @@
 from helpers import Session
 from helpers import Record
 
-import instance
+from openerp.workflow.instance import WorkflowInstance
+# import instance
 
 
 class WorkflowService(object):
@@ -49,7 +50,7 @@ class WorkflowService(object):
             (self.record.id or None, self.record.model or None, 'active')
         )
         for (instance_id,) in self.cr.fetchall():
-            instance.update(self.session, self.record, instance_id)
+            WorkflowInstance(self.session, self.record, {'id': instance_id}).update()
 
     def trigger(self):
         self.cr.execute('select instance_id from wkf_triggers where res_id=%s and model=%s', (self.record.id, self.record.model))
@@ -61,10 +62,10 @@ class WorkflowService(object):
             current_session = Session(self.session.cr, current_uid)
             current_record = Record(current_model_name, current_record_id)
 
-            instance.update(current_session, current_record, instance_id)
+            WorkflowInstance(current_session, current_record, {'id': instance_id}).update()
 
     def delete(self):
-        instance.delete(self.session, self.record)
+        WorkflowInstance(self.session, self.record, {}).delete()
 
     def create(self):
         WorkflowService.CACHE.setdefault(self.cr.dbname, {})
@@ -77,14 +78,18 @@ class WorkflowService(object):
             WorkflowService.CACHE[self.cr.dbname][self.record.model] = wkf_ids
 
         for (wkf_id, ) in wkf_ids:
-            instance.create(self.session, self.record, wkf_id)
+            WorkflowInstance.create(self.session, self.record, wkf_id)
 
     def validate(self, signal):
         result = False
         # ids of all active workflow instances for a corresponding resource (id, model_nam)
         self.cr.execute('select id from wkf_instance where res_id=%s and res_type=%s and state=%s', (self.record.id, self.record.model, 'active'))
+        # TODO: Refactor the workflow instance object
         for (instance_id,) in self.cr.fetchall():
-            res2 = instance.validate(self.session, self.record, instance_id, signal)
+            wi = WorkflowInstance(self.session, self.record, {'id': instance_id})
+
+            res2 = wi.validate(signal)
+
             result = result or res2
         return result
 
diff --git a/openerp/workflow/workitem.py b/openerp/workflow/workitem.py
index 7d0afcb519f..2c71aaaf7d8 100644
--- a/openerp/workflow/workitem.py
+++ b/openerp/workflow/workitem.py
@@ -60,235 +60,191 @@ class Environment(dict):
         else:
             return super(Environment, self).__getitem__(key)
 
-def wkf_expr_eval_expr(session, record, workitem, lines):
-    """
-    Evaluate each line of ``lines`` with the ``Environment`` environment, returning
-    the value of the last line.
-    """
-    assert lines, 'You used a NULL action in a workflow, use dummy node instead.'
-    result = False
-    for line in lines.split('\n'):
-        line = line.strip()
-        if not line:
-            continue
-        if line == 'True':
-            result = True
-        elif line == 'False':
-            result = False
-        else:
-            env = Environment(session, record)
-            result = eval(line, env, nocopy=True)
-    return result
-
-def wkf_expr_execute_action(session, record, workitem, activity):
-    """
-    Evaluate the ir.actions.server action specified in the activity.
-    """
-    ir_actions_server = openerp.registry(session.cr.dbname)['ir.actions.server']
-    context = { 'active_model': record.model, 'active_id': record.id, 'active_ids': [record.id] }
-    result = ir_actions_server.run(session.cr, session.uid, [activity['action_id']], context)
-    return result
-
-def wkf_expr_execute(session, record, workitem, activity):
-    """
-    Evaluate the action specified in the activity.
-    """
-    return wkf_expr_eval_expr(session, record, workitem, activity['action'])
-
-def wkf_expr_check(session, record, workitem, transition, signal):
-    """
-    Test if a transition can be taken. The transition can be taken if:
-
-    - the signal name matches,
-    - the uid is SUPERUSER_ID or the user groups contains the transition's
-      group,
-    - the condition evaluates to a truish value.
-    """
-    if transition['signal'] and signal != transition['signal']:
-        return False
-
-    if session.uid != openerp.SUPERUSER_ID and transition['group_id']:
-        registry = openerp.registry(session.cr.dbname)
-        user_groups = registry['res.users'].read(session.cr, session.uid, [session.uid], ['groups_id'])[0]['groups_id']
-        if transition['group_id'] not in user_groups:
-            return False
-
-    return wkf_expr_eval_expr(session, record, workitem, transition['condition'])
-
 
 class WorkflowItem(object):
-    def __init__(self, session, record):
+    def __init__(self, session, record, work_item_values):
         assert isinstance(session, Session)
         assert isinstance(record, Record)
         self.session = session
         self.record = record
 
-    def create(self, activities, instance_id, stack):
-        assert isinstance(activities, list)
+        if not work_item_values:
+            work_item_values = {}
+
+        assert isinstance(work_item_values, dict)
+        self.workitem = work_item_values
+
+    @classmethod
+    def create(cls, session, record, activity, instance_id, stack):
+        assert isinstance(session, Session)
+        assert isinstance(record, Record)
+        assert isinstance(activity, dict)
         assert isinstance(instance_id, (long, int))
         assert isinstance(stack, list)
 
-        cr = self.session.cr
+        cr = session.cr
+        cr.execute("select nextval('wkf_workitem_id_seq')")
+        id_new = cr.fetchone()[0]
+        cr.execute("insert into wkf_workitem (id,act_id,inst_id,state) values (%s,%s,%s,'active')", (id_new, activity['id'], instance_id))
+        cr.execute('select * from wkf_workitem where id=%s',(id_new,))
+        work_item_values = cr.dictfetchone()
+        logger.info('Created workflow item in activity %s',
+                    activity['id'],
+                    extra={'ident': (session.uid, record.model, record.id)})
+
+        workflow_item = WorkflowItem(session, record, work_item_values)
+        workflow_item.process(stack=stack)
+
+    @classmethod
+    def create_all(cls, session, record, activities, instance_id, stack):
+        assert isinstance(activities, list)
+
         for activity in activities:
-            cr.execute("select nextval('wkf_workitem_id_seq')")
-            id_new = cr.fetchone()[0]
-            cr.execute("insert into wkf_workitem (id,act_id,inst_id,state) values (%s,%s,%s,'active')", (id_new, activity['id'], instance_id))
-            cr.execute('select * from wkf_workitem where id=%s',(id_new,))
-            work_item = cr.dictfetchone()
-            logger.info('Created workflow item in activity %s',
-                        activity['id'],
-                        extra={'ident': (self.session.uid, self.record.model, self.record.id)})
+            cls.create(session, record, activity, instance_id, stack)
 
-            self.process(work_item, stack=stack)
-
-    def process(self, workitem, signal=None, force_running=False, stack=None):
-        assert isinstance(workitem, dict)
+    def process(self, signal=None, force_running=False, stack=None):
         assert isinstance(force_running, bool)
-
-        # return _process(self.session, self.record, work_item, signal=signal, force_running=force_running, stack=stack)
-        # assert isinstance(force_running, bool)
-
         assert stack is not None
 
         cr = self.session.cr
 
-        cr.execute('select * from wkf_activity where id=%s', (workitem['act_id'],))
+        cr.execute('select * from wkf_activity where id=%s', (self.workitem['act_id'],))
         activity = cr.dictfetchone()
 
         triggers = False
-        if workitem['state'] == 'active':
+        if self.workitem['state'] == 'active':
             triggers = True
-            if not self._execute(workitem, activity, stack):
+            if not self._execute(activity, stack):
                 return False
 
-        if force_running or workitem['state'] == 'complete':
-            ok = self._split_test(workitem, activity['split_mode'], signal, stack)
+        if force_running or self.workitem['state'] == 'complete':
+            ok = self._split_test(activity['split_mode'], signal, stack)
             triggers = triggers and not ok
 
         if triggers:
-            cr.execute('select * from wkf_transition where act_from=%s', (workitem['act_id'],))
+            cr.execute('select * from wkf_transition where act_from=%s', (self.workitem['act_id'],))
             for trans in cr.dictfetchall():
                 if trans['trigger_model']:
-                    ids = wkf_expr_eval_expr(self.session, self.record, workitem, trans['trigger_expr_id'])
+                    ids = self.wkf_expr_eval_expr(trans['trigger_expr_id'])
                     for res_id in ids:
                         cr.execute('select nextval(\'wkf_triggers_id_seq\')')
                         id =cr.fetchone()[0]
-                        cr.execute('insert into wkf_triggers (model,res_id,instance_id,workitem_id,id) values (%s,%s,%s,%s,%s)', (trans['trigger_model'],res_id,workitem['inst_id'], workitem['id'], id))
+                        cr.execute('insert into wkf_triggers (model,res_id,instance_id,workitem_id,id) values (%s,%s,%s,%s,%s)', (trans['trigger_model'],res_id, self.workitem['inst_id'], self.workitem['id'], id))
 
         return True
 
-    def _execute(self, workitem, activity, stack):
+    def _execute(self, activity, stack):
         """Send a signal to parenrt workflow (signal: subflow.signal_name)"""
         result = True
         cr = self.session.cr
         signal_todo = []
 
-        if (workitem['state']=='active') and activity['signal_send']:
+        if (self.workitem['state']=='active') and activity['signal_send']:
             # signal_send']:
-            cr.execute("select i.id,w.osv,i.res_id from wkf_instance i left join wkf w on (i.wkf_id=w.id) where i.id IN (select inst_id from wkf_workitem where subflow_id=%s)", (workitem['inst_id'],))
+            cr.execute("select i.id,w.osv,i.res_id from wkf_instance i left join wkf w on (i.wkf_id=w.id) where i.id IN (select inst_id from wkf_workitem where subflow_id=%s)", (self.workitem['inst_id'],))
             for instance_id, model_name, record_id in cr.fetchall():
                 record = Record(model_name, record_id)
                 signal_todo.append((instance_id, record, activity['signal_send']))
 
 
         if activity['kind'] == WorkflowActivity.KIND_DUMMY:
-            if workitem['state']=='active':
-                self._state_set(workitem, activity, 'complete')
+            if self.workitem['state']=='active':
+                self._state_set(activity, 'complete')
                 if activity['action_id']:
-                    res2 = wkf_expr_execute_action(self.session, self.record, workitem, activity)
+                    res2 = self.wkf_expr_execute_action(activity)
                     if res2:
                         stack.append(res2)
                         result=res2
 
         elif activity['kind'] == WorkflowActivity.KIND_FUNCTION:
 
-            if workitem['state']=='active':
-                self._state_set(workitem, activity, 'running')
-                returned_action = wkf_expr_execute(self.session, self.record, workitem, activity)
+            if self.workitem['state']=='active':
+                self._state_set(activity, 'running')
+                returned_action = self.wkf_expr_execute(activity)
                 if type(returned_action) in (dict,):
                     stack.append(returned_action)
                 if activity['action_id']:
-                    res2 = wkf_expr_execute_action(self.session, self.record, workitem, activity)
+                    res2 = self.wkf_expr_execute_action(activity)
                     # A client action has been returned
                     if res2:
                         stack.append(res2)
                         result=res2
-                self._state_set(workitem, activity, 'complete')
+                self._state_set(activity, 'complete')
 
         elif activity['kind'] == WorkflowActivity.KIND_STOPALL:
-            if workitem['state']=='active':
-                self._state_set(workitem, activity, 'running')
-                cr.execute('delete from wkf_workitem where inst_id=%s and id<>%s', (workitem['inst_id'], workitem['id']))
+            if self.workitem['state']=='active':
+                self._state_set(activity, 'running')
+                cr.execute('delete from wkf_workitem where inst_id=%s and id<>%s', (self.workitem['inst_id'], self.workitem['id']))
                 if activity['action']:
-                    wkf_expr_execute(self.session, self.record, workitem, activity)
-                self._state_set(workitem, activity, 'complete')
+                    self.wkf_expr_execute(activity)
+                self._state_set(activity, 'complete')
 
         elif activity['kind'] == WorkflowActivity.KIND_SUBFLOW:
 
-            if workitem['state']=='active':
+            if self.workitem['state']=='active':
 
-                self._state_set(workitem, activity, 'running')
+                self._state_set(activity, 'running')
                 if activity.get('action', False):
-                    id_new = wkf_expr_execute(self.session, self.record, workitem, activity)
+                    id_new = self.wkf_expr_execute(activity)
                     if not id_new:
-                        cr.execute('delete from wkf_workitem where id=%s', (workitem['id'],))
+                        cr.execute('delete from wkf_workitem where id=%s', (self.workitem['id'],))
                         return False
                     assert type(id_new)==type(1) or type(id_new)==type(1L), 'Wrong return value: '+str(id_new)+' '+str(type(id_new))
-                    cr.execute('select id from wkf_instance where res_id=%s and wkf_id=%s', (id_new,activity['subflow_id']))
+                    cr.execute('select id from wkf_instance where res_id=%s and wkf_id=%s', (id_new, activity['subflow_id']))
                     id_new = cr.fetchone()[0]
                 else:
-                    id_new = instance.create(self.session, self.record, activity['subflow_id'])
-                cr.execute('update wkf_workitem set subflow_id=%s where id=%s', (id_new, workitem['id']))
-                workitem['subflow_id'] = id_new
+                    inst = instance.WorkflowInstance(self.session, self.record)
+                    id_new = inst.create(activity['subflow_id'])
 
-            if workitem['state']=='running':
-                cr.execute("select state from wkf_instance where id=%s", (workitem['subflow_id'],))
-                state= cr.fetchone()[0]
+                cr.execute('update wkf_workitem set subflow_id=%s where id=%s', (id_new, self.workitem['id']))
+                self.workitem['subflow_id'] = id_new
+
+            if self.workitem['state']=='running':
+                cr.execute("select state from wkf_instance where id=%s", (self.workitem['subflow_id'],))
+                state = cr.fetchone()[0]
                 if state=='complete':
-                    self._state_set(workitem, activity, 'complete')
+                    self._state_set(activity, 'complete')
 
         for instance_id, record, signal_send in signal_todo:
-            instance.validate(self.session, self.record, signal_send, force_running=True)
+            wi = instance.WorkflowInstance(self.session, record, {'id': instance_id})
+            wi.validate(signal_send, force_running=True)
 
         return result
 
-    def _state_set(self, workitem, activity, state):
-        self.session.cr.execute('update wkf_workitem set state=%s where id=%s', (state, workitem['id']))
-        workitem['state'] = state
+    def _state_set(self, activity, state):
+        self.session.cr.execute('update wkf_workitem set state=%s where id=%s', (state, self.workitem['id']))
+        self.workitem['state'] = state
         logger.info('Changed state of work item %s to "%s" in activity %s',
-                    workitem['id'], state, activity['id'],
+                    self.workitem['id'], state, activity['id'],
                     extra={'ident': (self.session.uid, self.record.model, self.record.id)})
 
-
-
-
-    def _split_test(self, workitem, split_mode, signal, stack):
+    def _split_test(self, split_mode, signal, stack):
         cr = self.session.cr
-        cr.execute('select * from wkf_transition where act_from=%s', (workitem['act_id'],))
+        cr.execute('select * from wkf_transition where act_from=%s', (self.workitem['act_id'],))
         test = False
         transitions = []
         alltrans = cr.dictfetchall()
 
         if split_mode in ('XOR', 'OR'):
             for transition in alltrans:
-                if wkf_expr_check(self.session, self.record, workitem, transition,signal):
+                if self.wkf_expr_check(transition,signal):
                     test = True
-                    transitions.append((transition['id'], workitem['inst_id']))
+                    transitions.append((transition['id'], self.workitem['inst_id']))
                     if split_mode=='XOR':
                         break
         else:
             test = True
             for transition in alltrans:
-                if not wkf_expr_check(self.session, self.record, workitem, transition,signal):
+                if not self.wkf_expr_check(transition, signal):
                     test = False
                     break
-                cr.execute('select count(*) from wkf_witm_trans where trans_id=%s and inst_id=%s', (transition['id'], workitem['inst_id']))
+                cr.execute('select count(*) from wkf_witm_trans where trans_id=%s and inst_id=%s', (transition['id'], self.workitem['inst_id']))
                 if not cr.fetchone()[0]:
-                    transitions.append((transition['id'], workitem['inst_id']))
+                    transitions.append((transition['id'], self.workitem['inst_id']))
 
         if test and transitions:
             cr.executemany('insert into wkf_witm_trans (trans_id,inst_id) values (%s,%s)', transitions)
-            cr.execute('delete from wkf_workitem where id=%s', (workitem['id'],))
+            cr.execute('delete from wkf_workitem where id=%s', (self.workitem['id'],))
             for t in transitions:
                 self._join_test(t[0], t[1], stack)
             return True
@@ -299,7 +255,7 @@ class WorkflowItem(object):
         cr.execute('select * from wkf_activity where id=(select act_to from wkf_transition where id=%s)', (trans_id,))
         activity = cr.dictfetchone()
         if activity['join_mode']=='XOR':
-            self.create([activity], inst_id, stack)
+            WorkflowItem.create(self.session, self.record, activity, inst_id, stack=stack)
             cr.execute('delete from wkf_witm_trans where inst_id=%s and trans_id=%s', (inst_id,trans_id))
         else:
             cr.execute('select id from wkf_transition where act_to=%s', (activity['id'],))
@@ -314,7 +270,68 @@ class WorkflowItem(object):
             if ok:
                 for (id,) in trans_ids:
                     cr.execute('delete from wkf_witm_trans where trans_id=%s and inst_id=%s', (id,inst_id))
-                self.create([activity], inst_id, stack)
+                WorkflowItem.create(self.session, self.record, activity, inst_id, stack=stack)
+
+    def wkf_expr_eval_expr(self, lines):
+        """
+        Evaluate each line of ``lines`` with the ``Environment`` environment, returning
+        the value of the last line.
+        """
+        assert lines, 'You used a NULL action in a workflow, use dummy node instead.'
+        result = False
+        for line in lines.split('\n'):
+            line = line.strip()
+            if not line:
+                continue
+            if line == 'True':
+                result = True
+            elif line == 'False':
+                result = False
+            else:
+                env = Environment(self.session, self.record)
+                result = eval(line, env, nocopy=True)
+        return result
+
+    def wkf_expr_execute_action(self, activity):
+        """
+        Evaluate the ir.actions.server action specified in the activity.
+        """
+        context = {
+            'active_model': self.record.model,
+            'active_id': self.record.id,
+            'active_ids': [self.record.id]
+        }
+
+        ir_actions_server = openerp.registry(self.session.cr.dbname)['ir.actions.server']
+        result = ir_actions_server.run(self.session.cr, self.session.uid, [activity['action_id']], context)
+
+        return result
+
+    def wkf_expr_execute(self, activity):
+        """
+        Evaluate the action specified in the activity.
+        """
+        return self.wkf_expr_eval_expr(activity['action'])
+
+    def wkf_expr_check(self, transition, signal):
+        """
+        Test if a transition can be taken. The transition can be taken if:
+
+        - the signal name matches,
+        - the uid is SUPERUSER_ID or the user groups contains the transition's
+          group,
+        - the condition evaluates to a truish value.
+        """
+        if transition['signal'] and signal != transition['signal']:
+            return False
+
+        if self.session.uid != openerp.SUPERUSER_ID and transition['group_id']:
+            registry = openerp.registry(self.session.cr.dbname)
+            user_groups = registry['res.users'].read(self.session.cr, self.session.uid, [self.session.uid], ['groups_id'])[0]['groups_id']
+            if transition['group_id'] not in user_groups:
+                return False
+
+        return self.wkf_expr_eval_expr(transition['condition'])
 
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