A perfect hash function maps a static set of n keys into a set of m integer
numbers without collisions, where m is greater than or equal to n.  If m is
equal to n, the function is called minimal.

Minimal perfect hash functions are widely used for memory efficient storage
and fast retrieval of items from static sets, such as words in natural
languages, reserved words in programming languages or interactive systems,
universal resource locations (URLs) in Web search engines, or item sets in
data mining techniques.  Therefore, there are applications for minimal
perfect hash functions in information retrieval systems, database systems,
language translation systems, electronic commerce systems, compilers,
operating systems, among others.

WWW: http://cmph.sourceforge.net/