  Design methods in information systems frequently create software descriptions
using formal languages. Nonetheless, most software designers prefer to describe
software using natural languages. This distinction is not simply a matter of
convenience. Natural languages are not the same as formal languages; in
particular, natural languages do not follow the notions of equivalence used by
formal languages. In this paper, we show both the existence and coexistence of
different notions of equivalence by extending the no-tion of oracles used in
formal languages. This allows distinctions to be made between the trustworthy
oracles assumed by formal languages and the untrust-worthy oracles used by
natural languages. By examin-ing the notion of equivalence, we hope to
encourage designers of software to rethink the place of ambiguity in software
design.
