`mkid' is a simple, fast, high-capacity, language-independent
identifier database tool.  Actually, the term `identifier' is too
limiting--`mkid' stores tokens, be they program identifiers of any
form, literal numbers, or words of human-readable text.  Database
queries can be issued from the command-line, or from within emacs,
serving as an augmented tags facility.

WWW: http://www.gnu.org/software/idutils/