Current day database applications, with large numbers of users,
require fine-grained access control mechanisms, at the level of
individual tuples, not just entire relations/views. Fine-grained
access control is often enforced in the application code, which
has numerous drawbacks; these can be avoided by
specifying/enforcing access control at the database level.

In this talk, we first survey different approaches to fine-grained
authorization. We then present a novel fine-grained access
control model based on authorization views that allows
"authorization transparent" querying; that is, user queries can be
phrased in terms of the database relations, and are valid if they
can be answered using only the information contained in these
authorization views. We extend earlier work on
authorization-transparent querying by introducing a new notion of
validity, conditional validity. (The latter part of the talk
describes joint work with Rizvi, Mendelzon and Roy.)