Two extreme cases of choices for these factors
are searching using a pattern-matching utility such as grep, or searching using
an organization such as the Library of Congress. Searching a large text collection
using grep will have poor effectiveness and poor efficiency, but will be very cheap.
Searching using the staff analysts at the Library of Congress will produce excellent
results (high effectiveness) due to the manual effort involved, will be efficient
in terms of the user’s time (although it will involve a delay waiting for a response
from the analysts), and will be very expensive. Searching directly using an effective
search engine is designed to be a reasonable compromise between these extremes.