Reasoning from prior cases or abstractions requires that a system iden
tify relevant similarities between the current situation and objects r
epresented in memory. Often, relevance depends upon abstract, thematic
, costly-to-infer properties of the situation. Because of the cost of
inference, a case-retrieval system needs to learn which descriptions a
re worth inferring, and how costly the inference will be. This article
outlines the properties that make an abstract thematic feature valuab
le to a case-based reasoner, and recasts the problem of case retrieval
into a framework under which a system can explicitly and dynamically
reason about the cost of acquiring features relative to their informat
ion value.