The.Algorithm.Design.Manual.Springer-Verlag.1998

Approximate String Matching
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Approximate String Matching
Input description: A text string t and a pattern string p. An edit cost bound k.
Problem description: Can we transform t to p using at most k insertions, deletions, and substitutions?
Discussion: Approximate string matching is fundamental to text processing, because we live in an errorprone
world. Any spelling correction program must be able to identify the closest match for any text
string not found in a dictionary. Genbank has become a fundamental tool for molecular biology by
supporting homology (similarity) searches on DNA sequences. Suppose you were to sequence a new
gene in man, and you discovered that it is similar to the hemoglobin gene in rats. It is likely that this new
gene also produces hemoglobin, and any differences are the result of genetic mutations during evolution.
I once encountered approximate string matching in evaluating the performance of an optical character
recognition system that we built. After scanning and recognizing a test document, we needed to compare
the correct answers with those produced by our system. To improve our system, it was important to count
how often each pair of letters were getting confused and to identify gibberish when the program was
trying to make out letters where none existed. The solution was to do an alignment between the two texts.
Insertions and deletions corresponded to gibberish, while substitutions signaled errors in our recognizers.
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