The ZQueryHandler class is a utility class for Z39.50 search and scan -
It creates a query string from an input URL and invokes the
Z39.58 query parser to create a query string to pass the Z39.50
search and scan classes.
The ZUserData class is a core class to maintain information
of all the Z39.50 activity
for a user, from the search history, the list of Z39.50 databases
the user has access to, and the currently active Z39.50 connections.