  Even though library and archival practice, as well as Digital Preservation,
have a long tradition in identifying information objects, the question of their
precise identity under change of carrier or migration is still a riddle to
science. The objective of this paper is to provide criteria for the unique
identification of some important kinds of information objects, independent from
the kind of carrier or specific encoding. Our approach is based on the idea
that the substance of some kinds of information objects can completely be
described in terms of discrete arrangements of finite numbers of known kinds of
symbols, such as those implied by style guides for scientific journal
submissions. Our theory is also useful for selecting or describing what has to
be preserved. This is a fundamental problem since curators and archivists would
like to formally record the decisions of what has to be preserved over time and
to decide (or verify) whether a migration (transformation) preserves the
intended information content. Furthermore, it is important for reasoning about
the authenticity of digital objects, as well as for reducing the cost of
digital preservation.
