Why is there a tsquery data type?

Why does text search need a tsquery data type?  I realize it needs
tsvector so it can create indexes and updated trigger columns, but it
seems tsquery could instead just be a simple text string.

--  Bruce Momjian            http://momjian.us EnterpriseDB                               http://www.enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +