Abstract. Inconsistent contexts are death-wounds which usually result in contextaware applications' incongruous behaviors and users' perplexed feelings, therefore the benefits of context-aware computing will become less believed. This problem occurs in most sensor based applications due to the intrinsic drawbacks of fallible physical sensors which can only detect some evidence of real world's situations rather than global views of them. In this paper, we extend ontology based context modeling approach with some descriptive information added to contexts, modify reasoners to support time information, bring in a context lifecycle management strategy, establish a context exploitation mechanism, and propose an inconsistency resolution algorithm, fostering timely, exact and conflictfree contexts. Also, experiments are carried out to attest our design principles.