/* ** NOTE: This implementation was originally part of the WAIS system ** The main function, Stem(), was incorporated into Swish-E 1.1 ** to provide a stemming function. ** 11/24/98 Mark Gaulin ** ** Stem returns original word if words stems to empty string ** Bill Moseley 10/11/99 ** ** Repeats stemming until word will stem no more ** Bill Moseley 10/17/99 ** ** function: EndsWithCVC patched a bug. see below. Moseley 10/19/99 ** ** Added word length arg to ReplaceEnd and Stem to avoid strcat overflow ** 11/17/99 - SRE ** ** fixed int cast, missing return value, braces around initializations: problems pointed out by "gcc -Wall" ** SRE 2/22/00 ** ** Jose Ruiz 18/10/00 ** Remove static word from end var and make the code thread safe ** ** Bill Moseley 20/05/01 ** Rewrote to simplify. No more need to repeat stem (expandstar gone from search.c) ** got rid of most of the reallocation of memory. */ /* WIDE AREA INFORMATION SERVER SOFTWARE: No guarantees or restrictions. See the readme file for the full standard disclaimer. francois@welchgate.welch.jhu.edu */ /* Copyright (c) CNIDR (see ../COPYRIGHT) */ /* * stems a word. * */ /* the main functions are: * stemmer * */ #include "swish.h" #include #include #include #include "stemmer.h" #include "mem.h" #define FALSE 0 #define TRUE 1 /******************************* stem.c *********************************** Purpose: Implementation of the Porter stemming algorithm documented in: Porter, M.F., "An Algorithm For Suffix Stripping," Program 14 (3), July 1980, pp. 130-137. Provenance: Written by B. Frakes and C. Cox, 1986. Changed by C. Fox, 1990. - made measure function a DFA - restructured structs - renamed functions and variables - restricted function and variable scopes Changed by C. Fox, July, 1991. - added ANSI C declarations - branch tested to 90% coverage Notes: This code will make little sense without the the Porter article. The stemming function converts its input to lower case. **/ /************************ Standard Include Files *************************/ /*****************************************************************************/ /***************** Private Defines and Data Structures *******************/ #define IsVowel(c) ('a'==(c)||'e'==(c)||'i'==(c)||'o'==(c)||'u'==(c)) typedef struct { int id; /* returned if rule fired */ char *old_end; /* suffix replaced */ char *new_end; /* suffix replacement */ int old_offset; /* from end of word to start of suffix */ int new_offset; /* from beginning to end of new suffix */ int min_root_size; /* min root word size for replacement */ int (*condition) (); /* the replacement test function */ } RuleList; #define LAMBDA "" /* the constant empty string */ /*****************************************************************************/ /******************** Private Function Declarations **********************/ #ifdef __STDC__ int WordSize(char *word); int ContainsVowel(char *word); int EndsWithCVC(char *word); int AddAnE(char *word); int RemoveAnE(char *word); int ReplaceEnd(char *word, RuleList * rule); #else int WordSize( /* word */ ); int ContainsVowel( /* word */ ); int EndsWithCVC( /* word */ ); int AddAnE( /* word */ ); int RemoveAnE( /* word */ ); int ReplaceEnd( /* word, rule */ ); #endif /******************************************************************************/ /***************** Initialized Private Data Structures ********************/ /* 2/22/00 - added braces around each line */ static RuleList step1a_rules[] = { {101, "sses", "ss", 3, 1, -1, NULL,}, {102, "ies", "i", 2, 0, -1, NULL,}, {103, "ss", "ss", 1, 1, -1, NULL,}, {104, "s", LAMBDA, 0, -1, -1, NULL,}, {000, NULL, NULL, 0, 0, 0, NULL,} }; static RuleList step1b_rules[] = { {105, "eed", "ee", 2, 1, 0, NULL,}, {106, "ed", LAMBDA, 1, -1, -1, ContainsVowel,}, {107, "ing", LAMBDA, 2, -1, -1, ContainsVowel,}, {000, NULL, NULL, 0, 0, 0, NULL,} }; static RuleList step1b1_rules[] = { {108, "at", "ate", 1, 2, -1, NULL,}, {109, "bl", "ble", 1, 2, -1, NULL,}, {110, "iz", "ize", 1, 2, -1, NULL,}, {111, "bb", "b", 1, 0, -1, NULL,}, {112, "dd", "d", 1, 0, -1, NULL,}, {113, "ff", "f", 1, 0, -1, NULL,}, {114, "gg", "g", 1, 0, -1, NULL,}, {115, "mm", "m", 1, 0, -1, NULL,}, {116, "nn", "n", 1, 0, -1, NULL,}, {117, "pp", "p", 1, 0, -1, NULL,}, {118, "rr", "r", 1, 0, -1, NULL,}, {119, "tt", "t", 1, 0, -1, NULL,}, {120, "ww", "w", 1, 0, -1, NULL,}, {121, "xx", "x", 1, 0, -1, NULL,}, {122, LAMBDA, "e", -1, 0, -1, AddAnE,}, {000, NULL, NULL, 0, 0, 0, NULL,} }; static RuleList step1c_rules[] = { {123, "y", "i", 0, 0, -1, ContainsVowel,}, {000, NULL, NULL, 0, 0, 0, NULL,} }; static RuleList step2_rules[] = { {203, "ational", "ate", 6, 2, 0, NULL,}, {204, "tional", "tion", 5, 3, 0, NULL,}, {205, "enci", "ence", 3, 3, 0, NULL,}, {206, "anci", "ance", 3, 3, 0, NULL,}, {207, "izer", "ize", 3, 2, 0, NULL,}, {208, "abli", "able", 3, 3, 0, NULL,}, {209, "alli", "al", 3, 1, 0, NULL,}, {210, "entli", "ent", 4, 2, 0, NULL,}, {211, "eli", "e", 2, 0, 0, NULL,}, {213, "ousli", "ous", 4, 2, 0, NULL,}, {214, "ization", "ize", 6, 2, 0, NULL,}, {215, "ation", "ate", 4, 2, 0, NULL,}, {216, "ator", "ate", 3, 2, 0, NULL,}, {217, "alism", "al", 4, 1, 0, NULL,}, {218, "iveness", "ive", 6, 2, 0, NULL,}, {219, "fulnes", "ful", 5, 2, 0, NULL,}, {220, "ousness", "ous", 6, 2, 0, NULL,}, {221, "aliti", "al", 4, 1, 0, NULL,}, {222, "iviti", "ive", 4, 2, 0, NULL,}, {223, "biliti", "ble", 5, 2, 0, NULL,}, {000, NULL, NULL, 0, 0, 0, NULL,} }; static RuleList step3_rules[] = { {301, "icate", "ic", 4, 1, 0, NULL,}, {302, "ative", LAMBDA, 4, -1, 0, NULL,}, {303, "alize", "al", 4, 1, 0, NULL,}, {304, "iciti", "ic", 4, 1, 0, NULL,}, {305, "ical", "ic", 3, 1, 0, NULL,}, {308, "ful", LAMBDA, 2, -1, 0, NULL,}, {309, "ness", LAMBDA, 3, -1, 0, NULL,}, {000, NULL, NULL, 0, 0, 0, NULL,} }; static RuleList step4_rules[] = { {401, "al", LAMBDA, 1, -1, 1, NULL,}, {402, "ance", LAMBDA, 3, -1, 1, NULL,}, {403, "ence", LAMBDA, 3, -1, 1, NULL,}, {405, "er", LAMBDA, 1, -1, 1, NULL,}, {406, "ic", LAMBDA, 1, -1, 1, NULL,}, {407, "able", LAMBDA, 3, -1, 1, NULL,}, {408, "ible", LAMBDA, 3, -1, 1, NULL,}, {409, "ant", LAMBDA, 2, -1, 1, NULL,}, {410, "ement", LAMBDA, 4, -1, 1, NULL,}, {411, "ment", LAMBDA, 3, -1, 1, NULL,}, {412, "ent", LAMBDA, 2, -1, 1, NULL,}, {423, "sion", "s", 3, 0, 1, NULL,}, {424, "tion", "t", 3, 0, 1, NULL,}, {415, "ou", LAMBDA, 1, -1, 1, NULL,}, {416, "ism", LAMBDA, 2, -1, 1, NULL,}, {417, "ate", LAMBDA, 2, -1, 1, NULL,}, {418, "iti", LAMBDA, 2, -1, 1, NULL,}, {419, "ous", LAMBDA, 2, -1, 1, NULL,}, {420, "ive", LAMBDA, 2, -1, 1, NULL,}, {421, "ize", LAMBDA, 2, -1, 1, NULL,}, {000, NULL, NULL, 0, 0, 0, NULL,} }; static RuleList step5a_rules[] = { {501, "e", LAMBDA, 0, -1, 1, NULL,}, {502, "e", LAMBDA, 0, -1, -1, RemoveAnE,}, {000, NULL, NULL, 0, 0, 0, NULL,} }; static RuleList step5b_rules[] = { {503, "ll", "l", 1, 0, 1, NULL,}, {000, NULL, NULL, 0, 0, 0, NULL,} }; static RuleList *all_steps[] = { step1a_rules, step1b_rules, /* step1b1_rules, -- conditionaly called below */ step1c_rules, step2_rules, step3_rules, step4_rules, step5a_rules, step5b_rules, }; /*****************************************************************************/ /******************** Private Function Declarations **********************/ /*FN*************************************************************************** WordSize( word ) Returns: int -- a weird count of word size in adjusted syllables Purpose: Count syllables in a special way: count the number vowel-consonant pairs in a word, disregarding initial consonants and final vowels. The letter "y" counts as a consonant at the beginning of a word and when it has a vowel in front of it; otherwise (when it follows a consonant) it is treated as a vowel. For example, the WordSize of "cat" is 1, of "any" is 1, of "amount" is 2, of "anything" is 3. Plan: Run a DFA to compute the word size Notes: The easiest and fastest way to compute this funny measure is with a finite state machine. The initial state 0 checks the first letter. If it is a vowel, then the machine changes to state 1, which is the "last letter was a vowel" state. If the first letter is a consonant or y, then it changes to state 2, the "last letter was a consonant state". In state 1, a y is treated as a consonant (since it follows a vowel), but in state 2, y is treated as a vowel (since it follows a consonant. The result counter is incremented on the transition from state 1 to state 2, since this transition only occurs after a vowel-consonant pair, which is what we are counting. **/ int WordSize(char *word) { register int result; /* WordSize of the word */ register int state; /* current state in machine */ result = 0; state = 0; /* Run a DFA to compute the word size */ while ( *word ) { switch (state) { case 0: state = (IsVowel(*word)) ? 1 : 2; break; case 1: state = (IsVowel(*word)) ? 1 : 2; if (2 == state) result++; break; case 2: state = (IsVowel(*word) || ('y' == *word)) ? 1 : 2; break; } word++; } return (result); } /* WordSize */ /*FN************************************************************************** ContainsVowel( word, end ) Returns: int -- TRUE (1) if the word parameter contains a vowel, FALSE (0) otherwise. Purpose: Some of the rewrite rules apply only to a root containing a vowel, where a vowel is one of "aeiou" or y with a consonant in front of it. Plan: Obviously, under the definition of a vowel, a word contains a vowel iff either its first letter is one of "aeiou", or any of its other letters are "aeiouy". The plan is to test this condition. Notes: None **/ int ContainsVowel(char *word) { /* This isn't needed, right? */ if ( !*word ) return FALSE; return (IsVowel(*word) || (NULL != strpbrk(word + 1, "aeiouy"))); } /* ContainsVowel */ /*FN************************************************************************** EndsWithCVC( word ) Returns: int -- TRUE (1) if the current word ends with a consonant-vowel-consonant combination, and the second consonant is not w, x, or y, FALSE (0) otherwise. Purpose: Some of the rewrite rules apply only to a root with this characteristic. Plan: Look at the last three characters. Notes: None **/ int EndsWithCVC(char *word) { int length; /* for finding the last three characters */ if ((length = (int) strlen(word)) < 3) /* This was < 2 in original - Moseley 10/19/99 */ return (FALSE); return ( (NULL == strchr("aeiouwxy", (int)word[--length])) /* consonant */ && (NULL != strchr("aeiouy", (int)word[--length])) /* vowel */ && (NULL == strchr("aeiou", (int)word[--length])) ); /* consonant */ } /* EndsWithCVC */ /*FN************************************************************************** AddAnE( word ) Returns: int -- TRUE (1) if the current word meets special conditions for adding an e. Purpose: Rule 122 applies only to a root with this characteristic. Plan: Check for size of 1 and a consonant-vowel-consonant ending. Notes: None **/ int AddAnE(char *word) { return ((1 == WordSize(word)) && EndsWithCVC(word)); } /* AddAnE */ /*FN************************************************************************** RemoveAnE( word ) Returns: int -- TRUE (1) if the current word meets special conditions for removing an e. Purpose: Rule 502 applies only to a root with this characteristic. Plan: Check for size of 1 and no consonant-vowel-consonant ending. Notes: None **/ int RemoveAnE(char *word) { return ((1 == WordSize(word)) && !EndsWithCVC(word)); } /* RemoveAnE */ /*FN************************************************************************** ReplaceEnd( word, rule, end) Returns: int -- the id for the rule fired, 0 is none is fired Purpose: Apply a set of rules to replace the suffix of a word Plan: Loop through the rule set until a match meeting all conditions is found. If a rule fires, return its id, otherwise return 0. Connditions on the length of the root are checked as part of this function's processing because this check is so often made. Notes: This is the main routine driving the stemmer. It goes through a set of suffix replacement rules looking for a match on the current suffix. When it finds one, if the root of the word is long enough, and it meets whatever other conditions are required, then the suffix is replaced, and the function returns. **/ int ReplaceEnd(char *word, RuleList *rule) { char *ending; /* set to start of possible stemmed suffix */ char tmp_ch; /* save replaced character when testing */ char *end; /* pointer to last char of string */ end = word + strlen( word ) - 1; while ( rule->id ) { /* point ending to the start of the test sufix */ ending = end - rule->old_offset; /* is word long enough to contain suffix, and does it exist? */ if ( (word <= ending ) && (0 == strcmp(ending, rule->old_end)) ) { tmp_ch = *ending; /* in case we change our mind */ *ending = '\0'; if ( rule->min_root_size < WordSize(word) ) if (!rule->condition || (*rule->condition) ( word )) { /* replace the ending */ if ( (strlen( word ) + rule->new_offset + 1 ) >= MAXWORDLEN ) return STEM_WORD_TOO_BIG; strcat( word, rule->new_end ); return rule->id; } *ending = tmp_ch; /* nope, put it back */ } rule++; } return 0; } /* ReplaceEnd */ /*****************************************************************************/ /********************* Public Function Declarations **********************/ /*FN*************************************************************************** Stem( word ) Returns: int -- FALSE (0) if the word contains non-alphabetic characters and hence is not stemmed, TRUE (1) otherwise Purpose: Stem a word Plan: Part 1: Check to ensure the word is all alphabetic Part 2: Run through the Porter algorithm Part 3: Return an indication of successful stemming Notes: This function implements the Porter stemming algorithm, with a few additions here and there. See: Porter, M.F., "An Algorithm For Suffix Stripping," Program 14 (3), July 1980, pp. 130-137. Porter's algorithm is an ad hoc set of rewrite rules with various conditions on rule firing. The terminology of "step 1a" and so on, is taken directly from Porter's article, which unfortunately gives almost no justification for the various steps. Thus this function more or less faithfully refects the opaque presentation in the article. Changes from the article amount to a few additions to the rewrite rules; these are marked in the RuleList data structures with comments. **/ int Stem(char **inword, int *lenword) { char *end; /* pointer to the end of the word */ char word[MAXWORDLEN+1]; int length; int rule_result; /* which rule is fired in replacing an end */ // RuleList **rule; int i; /* Make sure the word is not too large from the start. */ if ( strlen( *inword ) >= MAXWORDLEN ) return STEM_WORD_TOO_BIG; /* make working copy */ strcpy( word, *inword ); /* Part 1: Check to ensure the word is all alphabetic */ /* no longer converts to lower case -- word should be lower before calling */ for ( end = word; *end; end++ ) if ( !isalpha( (unsigned int) *end ) ) return STEM_NOT_ALPHA; /* Part 2: Run through the Porter algorithm */ for (i = 0; i < sizeof(all_steps)/sizeof(all_steps[0]); i++) { rule_result = ReplaceEnd(word, all_steps[i]); if ((rule_result == 106) || (rule_result == 107)) rule_result = ReplaceEnd(word, step1b1_rules); if ( rule_result == STEM_WORD_TOO_BIG ) return rule_result; } length = strlen( word ); /* Stem must be two chars or more in length */ if ( length <= 1 ) return STEM_TO_NOTHING; /* reallocate memory if need more room */ if ( length >= *lenword ) { efree( *inword ); *lenword = length; *inword = emalloc( *lenword + 1 ); } strcpy( *inword, word ); return STEM_OK; }