
218 Topor and Sonenberg
answer whatever the domain of the interpretation. Such queries have been
called ''domain independent" and have been extensively studied (for example,
see Nicolas and Demolombe [1983]). Simple examples of unreasonable queries
are \/xp(x), whose truth depends on the domain of x, and —\ρ(χ,α), whose set
of correct answers depends on the domain of x.
In Topor [1986] it was observed that, for similar reasons, only certain
deductive databases could be regarded as reasonable, and the concept of
domain independent formulas was extended to that of domain independent
databases. A class of ''allowed'' databases was introduced,