  A query routing broker is a software agent that determines from a large set
of accessing information sources the ones most relevant to a user's information
need. As the number of information sources on the Internet increases
dramatically, future users will have to rely on query routing brokers to decide
a small number of information sources to query without incurring too much query
processing overheads. In this paper, we describe a query routing broker known
as ZBroker developed for bibliographic database servers that support the Z39.50
protocol. ZBroker samples the content of each bibliographic database by using
training queries and their results, and summarizes the bibliographic database
content into a knowledge base. We present the design and implementation of
ZBroker and describe its Web-based user interface.
