  Most cities in Germany regularly publish a booklet called the {\em
Mietspiegel}. It basically contains a verbal description of an expert system.
It allows the calculation of the estimated fair rent for a flat. By hand, one
may need a weekend to do so. With our computerized version, the {\em Munich
Rent Advisor}, the user just fills in a form in a few minutes and the rent is
calculated immediately. We also extended the functionality and applicability of
the {\em Mietspiegel} so that the user need not answer all questions on the
form. The key to computing with partial information using high-level
programming was to use constraint logic programming. We rely on the internet,
and more specifically the World Wide Web, to provide this service to a broad
user group. More than ten thousand people have used our service in the last
three years. This article describes the experiences in implementing and using
the {\em Munich Rent Advisor}. Our results suggests that logic programming with
constraints can be an important ingredient in intelligent internet systems.

Artificial Intelligence;Data Structures and Algorithms