This is done to group together words that may be spelled differently but have the same semantic meaning.
A person who types “astronomical” as a query term would most likely also be interested in documents that match the term “astronomy.”
Once the stemming process is completed, the algorithm calculates the frequency of each term.
Word frequency was used during the keyword selection process in the determination of good index terms.
However, other indexing algorithms could have been used instead with comparable results.