Automatic method of selecting multi-word key phrases from a document

Claim 1

An automatic method of selecting key phrases from a document presented in machine readable form to a processor, the document including a first multiplicity of words, some of the words forming phrases, the processor implementing the method by executing instructions stored in a memory device coupled to the processor, the method comprising the processor implemented steps of: a) generating from the document a multiplicity of phrases not including stop words; b) generating candidate phrases from the multiplicity of phrases, candidate phrases including more than one word and being composed of maximally long, non-overlapping subphrases, generating candidate phrases by the substeps of: b1) selecting a one of the multiplicity of phrases as a selected phrase; b2) selecting as a selected word a yet to be examined word of the selected phrase; b3) determining whether the selected word is a frequent word; b4) if the selected word is an infrequent: A) if all words of the selected phrase have not been examined, repeating steps b2) through b3); B) if all word of the selected phrase have been examined, repeating steps b1) through b3); C) if the selected word is a frequent word: C1) determining whether the selected word is an acceptable beginning for a key phrase by searching a list of bad beginning words; C2) if the selected word is not an acceptable beginning for a key phrase: i) determining whether all words of the selected phrase have been examined: ii) if all words of the selected phrase have not been examined, repeating steps b2) through b3); iii) if all words of the selected phrase have been examined, repeating steps b1) through b4); C3) if the selected word is an acceptable beginning for a key phrase: i) adding the selected word to a current phrase; ii) if all words of the selected phrase have not been examined selecting as a selected word a yet to be examined word of the selected phrase; iii) determining whether the selected word is a stop word; and iv) if the selected word is not a stop word, repeating steps C3i) through C3iii) c) selecting as key phrases a subset of most frequently occurring of the candidate phrases.