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Standard full-text search with TF/IDF treats documents, or at least each field
within a document, as a big bag of words. The
match query can tell us whether
that bag contains our search terms, but that is only part of the story.
It can’t tell us anything about the relationship between words.
Consider the difference between these sentences:
- Sue ate the alligator.
- The alligator ate Sue.
- Sue never goes anywhere without her alligator-skin purse.
match query for
sue alligator would match all three documents, but it
doesn’t tell us whether the two words form part of the same idea, or even the same
Understanding how words relate to each other is a complicated problem, and we can’t solve it by just using another type of query, but we can at least find words that appear to be related because they appear near each other or even right next to each other.
Each document may be much longer than the examples we have presented:
alligator may be separated by paragraphs of other text. Perhaps we still
want to return these documents in which the words are widely separated, but we
want to give documents in which the words are close together a higher relevance
This is the province of phrase matching, or proximity matching.
In this chapter, we are using the same example documents that we used for