  We propose a new approach to belief revision that provides a way to change
knowledge bases with a minimum of effort. We call this way of revising belief
states optimal belief revision. Our revision method gives special attention to
the fact that most belief revision processes are directed to a specific
informational objective. This approach to belief change is founded on notions
such as optimal context and accessibility. For the sentential model of belief
states we provide both a formal description of contexts as sub-theories
determined by three parameters and a method to construct contexts. Next, we
introduce an accessibility ordering for belief sets, which we then use for
selecting the best (optimal) contexts with respect to the processing effort
involved in the revision. Then, for finitely axiomatizable knowledge bases, we
characterize a finite accessibility ranking from which the accessibility
ordering for the entire base is generated and show how to determine the ranking
of an arbitrary sentence in the language. Finally, we define the adjustment of
the accessibility ranking of a revised base of a belief set.
