To date, the intention-centered methodology has been dominating the researches on mental state model for agent. In this paper, after briefly analyzing shortcomings of the intention-centered methodology, we propose that belief, desire and obligation (BDO) should be regarded as primitive attributes to describe social agent's mental state and various societal phenomenon. Then, we develop BDO logic and its formal semantics, syntactically import reward, punish, commit and decommit, and give descriptions for such societal concepts as team, organization, and organizational intention. Finally, we review several representative works on BDI agent and make comparison between them and our works here. We regard BDO logic as an improvement of the famous BDI logic and as a more expressive framework for the description of social agents and group concepts.