So far, many nonmonotonic logics are available to deal with the problem of reasoning about completeness, consistency and priorities of the knowledge. The two representative formalisms of them are default reasoning and belief revision, on which the frameworks of Brewka’s default theories and Rodrigues’ structured clusters are based, respectively. In this paper, we present a framework with the metaformalism of open logic based on a partial-ordered partition model. Via this formalism, we give model-theoretic interpretations for the two frameworks above. Taking into account computational aspects, we define their corresponding epistemic processes in turn. In this sense, our framework can be viewed as a generalization of them. Our framework are particularly suitable for the reasoning of requirements evolution.