ADVICE ON Text/Data Retrieval Products

[Robert Felps]

I am interested in text/data retrieval systems for UNIX. I need something
that allows easy access to a UNIX directory structure of information.

I have heard of a few system offered by software vendors,

  Topic
  Knowledge Set
  Zyindex
  others

If you have any experience with any of these I would be very interested
in hearing your opinions. Also if you know of any Public Domain tools
that help End-Users retrieve text and data rapidly would be helpful.