'Resolve the event_start and event_end field selectors
@param event_start: the field selector for the event start field
@param event_end: the field selector for the event end field'

def resolve_timestamp(self, event_start, event_end):

    resource = self.resource
    rfields = self.rfields
    if (not event_start):
        table = resource.table
        for fname in ('date', 'start_date', 'created_on'):
            if (fname in table.fields):
                event_start = fname
                break
        if (event_start and (not event_end)):
            for fname in ('end_date',):
                if (fname in table.fields):
                    event_end = fname
                    break
    if (not event_start):
        raise SyntaxError(('No    time    stamps    found    in    %s' % table))
    start_rfield = resource.resolve_selector(event_start)
    if event_end:
        end_rfield = resource.resolve_selector(event_end)
    else:
        end_rfield = None
    rfields['event_start'] = start_rfield
    rfields['event_end'] = end_rfield
