'Filter the specified result based on query criteria.
@param result: A potential result.
@type result: L{sxbase.SchemaObject}
@return: True if result should be excluded.
@rtype: boolean'

def filter(self, result):

    if (result is None):
        return True
    reject = (result in self.history)
    if reject:
        log.debug('result    %s,    rejected    by\n%s', Repr(result), self)
    return reject
