<?php
/**
* SeekQuarry/Yioop --
* Open Source Pure PHP Search Engine, Crawler, and Indexer
*
* Copyright (C) 2009 - 2026 Chris Pollett chris@pollett.org
*
* LICENSE:
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*
* END LICENSE
*
* @author Chris Pollett chris@pollett.org
* @license https://www.gnu.org/licenses/ GPL3
* @link https://www.seekquarry.com/
* @copyright 2009 - 2026
* @filesource
*/
namespace seekquarry\yioop\locale\en_US\resources;
use seekquarry\yioop\configs as C;
use seekquarry\yioop\library\PhraseParser;
use seekquarry\yioop\library as L;
/**
* This class has a collection of methods for English locale specific
* tokenization. In particular, it has a stemmer, a stop word remover (for
* use mainly in word cloud creation), and a part of speech tagger (for
* question answering). The stemmer is my stab at implementing the
* Porter Stemmer algorithm
* presented http://tartarus.org/~martin/PorterStemmer/def.txt
* The code is based on the non-thread safe C version given by Martin Porter.
* Since PHP is single-threaded this should be okay.
* Here given a word, its stem is that part of the word that
* is common to all its inflected variants. For example,
* tall is common to tall, taller, tallest. A stemmer takes
* a word and tries to produce its stem.
*
* @author Chris Pollett
*/
class Tokenizer
{
/**
* Words we don't want to be stemmed
* @var array
*/
public static $no_stem_list = ["titanic", "programming", "fishing", 'ins',
"blues", "factorial", "pbs"];
/**
* Phrases we would like yioop to rewrite before performing a query
* @var array
*/
public static $semantic_rewrites = [
"ins" => 'uscis',
"mimetype" => 'mime',
"military" => 'armed forces',
'full metal alchemist' => 'fullmetal alchemist',
'bruce schnier' => 'bruce schneier',
'dragonball' => 'dragon ball',
];
/**
* Any unique identifier corresponding to the component of a triplet which
* can be answered using a question answer list
* @var string
*/
public static $question_token = "qqq";
/**
* List of adjective-like parts of speech that might appear in lexicon file
* @var array
*/
public static $adjective_type = ["JJ", "JJR", "JJS"];
/**
* List of adverb-like parts of speech that might appear in lexicon file
* @var array
*/
public static $adverb_type = ["RB", "RBR", "RBS"];
/**
* List of conjunction-like parts of speech that might appear in lexicon
* file
* @var array
*/
public static $conjunction_type = ["CC"];
/**
* List of determiner-like parts of speech that might appear in lexicon
* file
* @var array
*/
public static $determiner_type = ["DT", "PDT"];
/**
* List of noun-like parts of speech that might appear in lexicon file
* @var array
*/
public static $noun_type = ["NN", "NNS", "NNP", "NNPS", "PRP"];
/**
* List of verb-like parts of speech that might appear in lexicon file
* @var array
*/
public static $verb_type = ["VB", "VBD", "VBG", "VBN", "VBP", "VBZ"];
/**
* A list of frequently occurring terms for this locale which should
* be excluded from certain kinds of queries
* @var array
*/
public static $stop_words = ['a','able','about','above','abst',
'accordance','according','based','accordingly','across','act',
'actually','added','adj','affected','affecting','affects','after',
'afterwards','again','against','ah','all','almost','alone','along',
'already','also','although','always','am','among','amongst','an','and',
'announce','another','any','anybody','anyhow','anymore','anyone',
'anything','anyway','anyways','anywhere','apparently','approximately',
'are','aren','arent','arise','around','as','aside','ask','asking','at',
'auth','available','away','awfully','b','back','be','became','because',
'become','becomes','becoming','been','before','beforehand','begin',
'beginning','beginnings','begins','behind','being','believe','below',
'beside','besides','between','beyond','biol','both','brief','briefly',
'but','by','c','ca','came','can','cannot','cant','cause','causes',
'certain','certainly', 'click', 'co','com','come',
'comment', 'comments', 'comes','contain','containing',
'contains','could','couldnt','d','date','did','didnt',
'different','do','does','doesnt','doing',
'done','dont','down','downwards',
'due','during','e','each','ed','edu','effect','eg','eight','eighty',
'either','else','elsewhere','end',
'ending','enough','especially','et',
'et-al','etc','even','ever','every',
'everybody','everyone','everything'
,'everywhere','ex','except','f','far','few','ff','fifth','first',
'five','fix','followed','following','follows','for','former',
'formerly','forth','found','four','from','further','furthermore',
'g','gave','get','gets','getting','give','given','gives','giving','go',
'goes','gone','got','gotten','h','had','happens','hardly','has',
'hasnt','have','havent','having','he','hed','hence','her','here',
'hereafter','hereby','herein','heres','hereupon','hers','herself',
'hes','hi','hid','him','himself','his','hither','home','how','howbeit',
'however', 'http', 'https', 'hundred','i','id','ie','if','ill',
'im','immediate','immediately',
'importance','important','in','inc','indeed','index','information',
'instead','into','invention','inward','is','isnt','it','itd','itll',
'its','itself','ive','j','just','k','keep','keeps',
'kept','kg','km','know',
'known','knows','l','largely','last','lately',
'later','latter','latterly',
'least','less','lest','let','lets','like','liked','likely','line',
'little','ll','look','looking','looks','ltd','m','made','mainly',
'make','makes','many','may','maybe','me','mean','means','meantime',
'meanwhile','merely','mg','might','million','miss','ml','more',
'moreover','most','mostly','mr','mrs','much','mug','must','my',
'myself','n','na','name','namely','nay','nd','near','nearly',
'necessarily','necessary','need','needs','neither','never',
'nevertheless','new','next','nine','ninety','no',
'nobody','non','none','nonetheless','noone',
'nor','normally','nos','not',
'noted','nothing','now','nowhere','o','obtain',
'obtained','obviously','of',
'off','often','oh','ok','okay','old','omitted','on','once','one',
'ones','only','onto','or','ord','other','others',
'otherwise','ought','our','ours',
'ourselves','out','outside','over','overall','owing','own','p','page',
'pages','part','particular','particularly',
'past','per','perhaps','placed',
'please','plus','poorly','possible','possibly','potentially','pp',
'predominantly','present','previously',
'primarily','probably','promptly',
'proud','provides','put','q','que','quickly','quite','qv', 'quot',
'r','ran',
'rather','rd','re','readily','really','recent','recently','ref','refs',
'regarding','regardless','regards','related','relatively','research',
'respectively','resulted','resulting',
'results','right','run','s','said',
'same','saw','say','saying','says','sec',
'section','see','seeing','seem',
'seemed','seeming','seems',
'seen','self','selves','sent','seven','several',
'shall','she','shed','shell',
'shes','should','shouldnt','show','showed','shown','showns','shows',
'significant','significantly','similar','similarly','since',
'six','slightly',
'so','some','somebody','somehow','someone','somethan',
'something','sometime',
'sometimes','somewhat','somewhere','soon',
'sorry','specifically','specified',
'specify','specifying','still','stop','strongly','sub','substantially',
'successfully','such','sufficiently','suggest','sup','sure','t','take',
'taken','taking','tell','tends','th','than',
'thank','thanks','thanx','that',
'thatll','thats','thatve','the','their',
'theirs','them','themselves','then',
'thence','there','thereafter','thereby','thered','therefore','therein',
'therell','thereof','therere','theres','thereto','thereupon','thereve',
'these','they','theyd','theyll','theyre',
'theyve','think','this','those',
'thou','though','thoughh','thousand','throug',
'through','throughout','thru',
'thus','til', 'till','tip','to','together','too',
'took','toward','towards','tried',
'tries','truly','try','trying','ts','twice','two','u','un','under',
'unfortunately','unless','unlike','unlikely','until','unto','up',
'upon','ups','us','use','used','useful','usefully','usefulness',
'uses','using','usually','v','value','various','ve','very',
'via','viz','vol','vols','vs',
'w','want','wants','was','wasnt','way','we',
'wed','welcome','well','went',
'were','werent','weve','what','whatever',
'whatll','whats','when','whence',
'whenever','where','whereafter','whereas','whereby','wherein','wheres',
'whereupon','wherever','whether','which','while','whim','whither',
'who','whod','whoever','whole','wholl','whom','whomever','whos',
'whose','why','widely', 'will', 'willing','wish','with','within',
'without','wont','words','world',
'would','wouldnt','www','x','y','yes','yet','you','youd','youll',
'your','youre','yours','yourself','yourselves','youve','z','zero'];
/**
* storage used in computing the stem
* @var string
*/
private static $buffer;
/**
* Index of the current end of the word at the current state of computing
* its stem
* @var int
*/
private static $k;
/**
* Index to start of the suffix of the word being considered for
* manipulation
* @var int
*/
private static $j;
/**
* Do any global set up for tokenizer (none in the case of en-US)
*/
public function __construct()
{
}
/**
* Stub function which could be used for a word segmenter.
* Such a segmenter on input thisisabunchofwords would output
* this is a bunch of words
*
* @param string $pre_segment before segmentation
* @return string should return string with words separated by space
* in this case does nothing
*/
public static function segment($pre_segment)
{
return $pre_segment;
}
/**
* Removes the stop words from the page (used for Word Cloud generation)
*
* @param mixed $data either a string or an array of string to remove
* stop words from
* @return mixed $data with no stop words
*/
public static function stopwordsRemover($data)
{
static $pattern = "";
if (empty($pattern)) {
$pattern = '/\b(' . implode('|', self::$stop_words) . ')\b/ui';
}
$data = preg_replace($pattern, '', $data);
return $data;
}
/**
* This methods tries to handle punctuation in terms specific to the
* English language such as abbreviations.
*
* @param string &$string a string of words, etc which might involve such
* terms
*/
public function canonicalizePunctuatedTerms(&$string)
{
static $substitutions = [
//abbreviated titles
"/([mM]r|[mM]rs|[mM]s|[dD]r|dD]rs|[iI]n|".
"[cC]apt|[cC]pl|sS]t|fF]t|[vV]s)\.(\s*)(\p{Lu}|\Z)/u" => '$1 $3',
"/,(\p{Lu})\.(\s*)(\p{Lu}|\Z)/u" => '$1_ $3',
"/gimme/i" => "give me",
"/gonna/i" => "going to",
"/gotta/i" => "got to",
"/ma\'am/i" => "madam",
"/\'tis/i" => "it is",
"/\'twas/i" => "it was",
"/y\'all/i" => "you all",
"/I\'m/" => "I am",
"/I ain\'t/" => "I am not",
"/You ain\'t/i" => "you are not",
"/can\'t/i" => "cannot",
"/(why|who|which|when|what|this|that|there|how|" .
"it|everyone|one|he|she)\'s/i" => "$1 is",
"/is been/" => "has been",
"/is had/" => "has had",
// shan't
"/shan\'t/" => "shall not",
// contractions with not
"/\b(\p{L}+)\'d/" => ' $1 would',
// contractions with not
"/\b(\p{L}+)n\'t/" => ' $1 not',
// contractions with will
"/\b(\p{L}+)\'ll/" => ' $1 will',
// contractions with have
"/\b(\p{L}+)\'ve/" => ' $1 have',
// contractions with have
"/\b(\p{L}+)\'re/" => ' $1 are',
"/\b(\p{L}+)\'s/" => ' $1_pos_s'
];
static $patterns = [];
static $replacements = [];
if (empty($patterns)) {
$patterns = array_keys($substitutions);
$replacements = array_values($substitutions);
}
$string = preg_replace($patterns, $replacements, $string);
}
/**
* Takes a phrase and tags each term in it with its part of speech.
* So each term in the original phrase gets mapped to term~part_of_speech
* This tagger is based on a Brill tagger. It makes uses a lexicon
* consisting of words from the Brown corpus together with a list of
* part of speech tags that that word had in the Brown Corpus. These are
* used to get an initial part of speech (in word was not present than
* we assume it is a noun). From this a fixed set of rules is used to
* modify the initial tag if necessary.
*
* @param string $phrase text to add parts speech tags to
* @param bool $with_tokens whether to include the terms and the tags
* in the output string or just the part of speech tags
* @return string $tagged_phrase phrase where each term has ~part_of_speech
* appended ($with_tokens == true) or just space separated
* part_of_speech (!$with_tokens)
*/
public static function tagPartsOfSpeechPhrase($phrase, $with_tokens = true)
{
$tagged_tokens = self::tagTokenizePartOfSpeech($phrase);
$tagged_phrase = self::taggedPartOfSpeechTokensToString(
$tagged_tokens, $with_tokens);
return $tagged_phrase;
}
/**
* Split input text into terms and output an array with one element
* per term, that element consisting of array with the term token
* and the part of speech tag.
*
* @param string $text string to tag and tokenize
* @return array of pairs of the form ("token" => token_for_term,
* "tag"=> part_of_speech_tag_for_term) for one each token in $text
*/
public static function tagTokenizePartOfSpeech($text)
{
/* if run as own server dictionary only loaded once for all requests */
static $dictionary = [];
$lexicon_file = C\LOCALE_DIR . "/en_US/resources/lexicon.txt.gz";
if (empty($dictionary)) {
if (file_exists($lexicon_file)) {
$lex_data = gzdecode(file_get_contents($lexicon_file));
preg_match_all("/([^\s\,]+)[\s|\,]+([^\n]+)/u",
$lex_data, $lex_parts);
$dictionary = array_combine($lex_parts[1], $lex_parts[2]);
}
}
preg_match_all("/[\w\d]+/", $text, $matches);
$tokens = $matches[0];
$nouns = ['NN', 'NNS', 'NNP'];
$verbs = ['VBD', 'VBP', 'VB'];
$result = [];
$previous = ['token' => -1, 'tag' => -1];
$previous_token = -1;
// now using our dictionary we tag
$i = 0;
$tag_list = [];
foreach ($tokens as $token) {
$prev_tag_list = $tag_list;
$tag_list = [];
// default to a common noun
$current = ['token' => $token, 'tag' => 'NN'];
// remove trailing full stops
$token = mb_strtolower($token);
if ($token == "howto") {
$current['tag'] = 'WP';
} else if (!empty($dictionary[$token])) {
$tag_list = explode(" ", $dictionary[$token]);
$current['tag'] = $tag_list[0];
}
// Converts verbs after 'the' to nouns
if ($previous['token'] == 'the' &&
in_array($current['tag'], $verbs)){
$current['tag'] = 'NN';
}
// Convert noun to number if . appears
if ($current['tag'][0] == 'N' && str_contains($token, '.')) {
$current['tag'] = 'CD';
}
$ends_with = substr($token, -2);
switch ($ends_with) {
case 'ed':
// Convert noun to past particle if ends with 'ed'
if ($current['tag'][0] == 'N') {
$current['tag'] = 'VBN';
}
break;
case 'ly':
// Anything that ends 'ly' is an adverb
$current['tag'] = 'RB';
break;
case 'al':
// Common noun to adjective if it ends with al
if (in_array($current['tag'], $nouns)) {
$current['tag'] = 'JJ';
}
break;
}
// Noun to verb if the word before is 'would'
if ($current['tag'] == 'NN' && $previous_token == 'would') {
$current['tag'] = 'VB';
}
// Convert common noun to gerund
if (in_array($current['tag'], $nouns) &&
str_ends_with($token, 'ing')) {
$current['tag'] = 'VBG';
}
//nouns followed by adjectives
if (in_array($previous['tag'], $nouns) &&
$current['tag'] == 'JJ' && in_array('JJ', $prev_tag_list)) {
$result[$i - 1]['tag'] = 'JJ';
$current['tag'] = 'NN';
}
/* If we have a noun, and the second can be a verb,
* convert to verb; if noun noun and previous could be an
* adjective convert to adjective
*/
if (in_array($previous['tag'], $nouns) &&
in_array($current['tag'], $nouns) ) {
if (in_array('VBN', $tag_list)) {
$current['tag'] = 'VBN';
} else if (in_array('VBZ', $tag_list)) {
$current['tag'] = 'VBZ';
} else if (in_array('JJ', $prev_tag_list)) {
$result[$i - 1]['tag'] = 'JJ';
}
}
$result[$i] = $current;
$i++;
$previous = $current;
$previous_token = $token;
}
return $result;
}
/**
* Takes a phrase query entered by user and return true if it is question
* and false if not
*
* @param $phrase any statement
* @return bool returns true if statement is question
*/
public function isQuestion($phrase)
{
$regex_starts_with_que =
"/^(who|what|which|where|when|whose|how)(.*)$/";
if (preg_match($regex_starts_with_que, trim($phrase))) {
return true;
}
return false;
}
/**
* Computes the stem of an English word
*
* For example, jumps, jumping, jumpy, all have jump as a stem
*
* @param string $word the string to stem
* @return string the stem of $words
*/
public static function stem($word)
{
if (in_array($word, self::$no_stem_list)) {
return $word;
}
// for hyphenated words, only stem last word -- my change CP
if (($last_hyphen = strrpos($word, "-")) > 0) {
$before_hyphen = substr($word, 0, $last_hyphen + 1);
$after_hyphen = substr($word, $last_hyphen + 1);
return $before_hyphen . self::stem($after_hyphen);
}
self::$buffer = $word;
self::$k = strlen($word) - 1;
self::$j = self::$k;
if (self::$k <= 1) {
return $word;
}
self::step1ab();
self::step1c();
self::step2();
self::step3();
self::step4();
self::step5();
return substr(self::$buffer, 0, self::$k + 1);
}
/**
* Take in a sentence and try to compress it to a smaller version
* that "retains the most important information and remains grammatically
* correct" (Jing 2000).
*
* @param string $sentence_to_compress the sentence to compress
* @return the compressed sentence
*/
public static function compressSentence($sentence_to_compress)
{
// patterns are based on From Back to Basics: CLASSY 2006 page 3:
static $delete_patterns = [
/*
2. We remove many adverbs and all conjunctions,
including phrases such as "As a matter of fact," and
"At this point," that occur at the start of a sentence.
*/
"/^At this point,?\b/i", "/^As a matter of fact,?\b/i",
"/^[a-zA-Z]*ly\b/i", "/(^and,?\b)|(^but,?\b)|(^for,?\b)|" .
"(^nor,?\b)|(^or,?\b)|(^so,?\b)|(^yet,?\b)/i",
/*
3. We remove a small selections of words that occur in the middle
of a sentence, such as ", however," and ", also," (not always
requiring the commas).
*/
"/(;|,)?\s*(nevertheless|today|tomorrow|soon|instead|in practice|" .
"however|as a practical matter|further(more)?|".
"as such|also)\s*(;|,)?\s*/i",
/*
4. For DUC 2006, we added the removal of ages such as ", 51," or
", aged 24,".
*/
"/,\s?\d{1,3},/i", "/,\s?aged\s?\d{1,3},/i",
/*
6. We remove relative clause attributives (clauses beginning with
"who(m)", "which", "when", and "where") wherever possible.
*/
"/(,\s?whom?[^,]*,)|(,\s?which[^,]*,)|" .
"(,\s?when[^,]*,)|(,\s?where[^,]*,)/i"
];
return preg_replace($delete_patterns, " ", $sentence_to_compress);
}
/**
* Takes a triplets array with subject, predicate, object fields with
* CONCISE and RAW subfields and rearranges it to have two fields CONCISE
* and RAW with subject, predicate, object, and QUESTION_ANSWER_LIST
* subfields
*
* @param array $sub_pred_obj_triplets in format described above
* @return array $processed_triplets in format described above
*/
public static function rearrangeTripletsByType($sub_pred_obj_triplets)
{
$processed_triplet = [];
$processed_triplets['CONCISE'] =
self::extractTripletByType($sub_pred_obj_triplets, "CONCISE");
$processed_triplets['RAW'] =
self::extractTripletByType($sub_pred_obj_triplets, "RAW");
return $processed_triplets;
}
/**
* Starting at the $cur_node in a $tagged_phrase parse tree for an English
* sentence, create a phrase string for each of the next nodes
* which belong to part of speech group $type.
*
* @param array &$cur_node node within parse tree
* @param array $tagged_phrase parse tree for phrase
* @param string $type self::$noun_type, self::$verb_type, etc
* @return string phrase string involving only terms of that $type
*/
public static function parseTypeList(&$cur_node, $tagged_phrase, $type)
{
$string = "";
$previous_string = "";
$previous_tag = "";
$start_node = $cur_node;
$next_tag = (empty($tagged_phrase[$cur_node]['tag'])) ? "" :
trim($tagged_phrase[$cur_node]['tag']);
$allowed_conjuncts = [];
while ($next_tag && (in_array($next_tag, $type) ||
in_array($next_tag, $allowed_conjuncts))) {
$previous_string = $string;
$string .= " ". $tagged_phrase[$cur_node]['token'];
$cur_node++;
$allowed_conjuncts = self::$conjunction_type;
$previous_tag = $next_tag;
$next_tag = (empty($tagged_phrase[$cur_node]['tag'])) ? "" :
trim($tagged_phrase[$cur_node]['tag']);
}
if (in_array($previous_tag, $allowed_conjuncts) && $start_node <
$cur_node) {
$cur_node--;
$string = $previous_string;
}
return $string;
}
/**
* Takes a part-of-speech tagged phrase and pre-tree with a
* parse-from position and builds a parse tree for an adjective if possible
*
* @param array $tagged_phrase
* an array of pairs of the form ("token" => token_for_term,
* "tag"=> part_of_speech_tag_for_term)
* @param array $tree that consists of ["cur_node" =>
* current parse position in $tagged_phrase]
* @return array has fields
* "cur_node" index of how far we parsed $tagged_phrase
* "JJ" a subarray with a token node for the adjective that was
* parsed
*/
public static function parseAdjective($tagged_phrase, $tree)
{
$adjective_string = self::parseTypeList($tree['cur_node'],
$tagged_phrase, self::$adjective_type);
if (!empty($adjective_string)) {
$tree["JJ"] = $adjective_string;
}
return $tree;
}
/**
* Takes a part-of-speech tagged phrase and pre-tree with a
* parse-from position and builds a parse tree for a determiner if possible
*
* @param array $tagged_phrase
* an array of pairs of the form ("token" => token_for_term,
* "tag"=> part_of_speech_tag_for_term)
* @param array $tree that consists of ["curnode" =>
* current parse position in $tagged_phrase]
* @return array has fields
* "cur_node" index of how far we parsed $tagged_phrase
* "DT" a subarray with a token node for the determiner that was
* parsed
*/
public static function parseDeterminer($tagged_phrase, $tree)
{
$determiner_string = "";
/* In: All the cows low, "All the" is considered a determiner.
That is, we will mush together the predeterminer with the determiner
*/
$determiner_string = self::parseTypeList($tree['cur_node'],
$tagged_phrase, self::$determiner_type);
if (!empty($determiner_string)) {
$tree["DT"] = $determiner_string;
}
return $tree;
}
/**
* Takes a part-of-speech tagged phrase and pre-tree with a
* parse-from position and builds a parse tree for a noun if possible
*
* @param array $tagged_phrase
* an array of pairs of the form ("token" => token_for_term,
* "tag"=> part_of_speech_tag_for_term)
* @param array $tree that consists of ["curnode" =>
* current parse position in $tagged_phrase]
* @return array has fields
* "cur_node" index of how far we parsed $tagged_phrase
* "NN" a subarray with a token node for the noun string that was
* parsed
*/
public static function parseNoun($tagged_phrase, $tree)
{
//Combining multiple noun into one
$noun_string = self::parseTypeList($tree['cur_node'], $tagged_phrase,
self::$noun_type);
if (!empty($noun_string)) {
$tree["NN"] = $noun_string;
}
return $tree;
}
/**
* Takes a part-of-speech tagged phrase and pre-tree with a
* parse-from position and builds a parse tree for a verb if possible
*
* @param array $tagged_phrase
* an array of pairs of the form ("token" => token_for_term,
* "tag"=> part_of_speech_tag_for_term)
* @param array $tree that consists of ["curnode" =>
* current parse position in $tagged_phrase]
* @return array has fields
* "cur_node" index of how far we parsed $tagged_phrase
* "VB" a subarray with a token node for the verb string that was
* parsed
*/
public static function parseVerb($tagged_phrase, $tree)
{
$verb_string = self::parseTypeList($tree['cur_node'], $tagged_phrase,
self::$verb_type);
if (!empty($verb_string)) {
$tree["VB"] = $verb_string;
}
return $tree;
}
/**
* Takes a part-of-speech tagged phrase and pre-tree with a
* parse-from position and builds a parse tree for a sequence of
* prepositional phrases if possible
*
* @param array $tagged_phrase
* an array of pairs of the form ("token" => token_for_term,
* "tag"=> part_of_speech_tag_for_term)
* @param array $tree that consists of ["cur_node" =>
* current parse position in $tagged_phrase]
* @param int $index which term in $tagged_phrase to start to try to parse
* a preposition from
* @return array has fields
* "cur_node" index of how far we parsed $tagged_phrase
* parsed followed by additional possible fields (here i
* represents the ith clause found):
* "IN_i" with value a preposition subtree
* "DT_i" with value a determiner subtree
* "JJ_i" with value an adjective subtree
* "NN_i" with value an additional noun subtree
*/
public static function parsePrepositionalPhrases($tagged_phrase, $tree,
$index = 1)
{
$cur_node = $tree['cur_node'];
// Checking for preposition. I.e, format: prep [det] [adjective] noun
if (isset($tagged_phrase[$cur_node]['tag']) &&
trim($tagged_phrase[$cur_node]['tag']) == "IN") {
/* can have multiple prep's in a row, for example,
it is known in over 20 countries*/
$preposition_string = self::parseTypeList($cur_node, $tagged_phrase,
["IN"]);
if (!empty($preposition_string)) {
$tree["IN_$index"] = $preposition_string;
}
$determiner_string = self::parseTypeList($cur_node, $tagged_phrase,
self::$determiner_type);
if (!empty($determiner_string)) {
$tree["DT_$index"] = $determiner_string;
}
$adjective_string = self::parseTypeList($cur_node, $tagged_phrase,
self::$adjective_type);
if (!empty($adjective_string)) {
$tree["JJ_$index"] = $adjective_string;
}
$prep_noun_string = self::parseTypeList($cur_node, $tagged_phrase,
self::$noun_type);
if ($prep_noun_string) {
$tree["NP_$index"] = $prep_noun_string;
}
/* if have more than one phrase in a row:
the drought happened in many countries over many years.
*/
$tree_next = self::parsePrepositionalPhrases($tagged_phrase,
["cur_node" => $cur_node], $index + 1);
unset($tree_next['cur_node']);
$tree['PRP'] = $tree_next;
}
$tree['cur_node'] = $cur_node;
return $tree;
}
/**
* Takes a part-of-speech tagged phrase and pre-tree with a
* parse-from position and builds a parse tree for a noun phrase if possible
*
* @param array $tagged_phrase
* an array of pairs of the form ("token" => token_for_term,
* "tag"=> part_of_speech_tag_for_term)
* @param array $tree that consists of ["curnode" =>
* current parse position in $tagged_phrase]
* @return array has fields
* "cur_node" index of how far we parsed $tagged_phrase
* "NP" a subarray with possible fields
* "DT" with value a determiner subtree
* "JJ" with value an adjective subtree
* "NN" with value a noun tree
*/
public static function parseNounPhrase($tagged_phrase, $tree)
{
$cur_node = $tree['cur_node'];
$tree_dt = self::parseDeterminer($tagged_phrase,
['cur_node' => $cur_node]);
$tree_jj = self::parseAdjective($tagged_phrase,
['cur_node' => $tree_dt['cur_node']]);
$tree_nn = self::parseNoun($tagged_phrase,
['cur_node' => $tree_jj['cur_node']]);
if ($tree_nn['cur_node'] == $cur_node) {
$tree['NP'] = "";
return $tree;
}
$tree_pp = self::parsePrepositionalPhrases($tagged_phrase,
['cur_node' => $tree_nn['cur_node']]);
$tree_aux = self::parseAuxClause($tagged_phrase,
['cur_node' => $tree_pp['cur_node']]);
$cur_node = $tree_aux['cur_node'];
$cc = "";
if (!empty($tagged_phrase[$cur_node]['tag']) &&
in_array($tagged_phrase[$cur_node]['tag'],
self::$conjunction_type)) {
$cc = $tagged_phrase[$cur_node]['token'];
$cur_node++;
}
$tree_np = self::parseNounPhrase($tagged_phrase,
['cur_node' => $cur_node]);
if ($tree_np['cur_node'] == $cur_node && $cc) {
$cur_node--;
$tree_np = [];
$cc = "";
} else {
$cur_node = $tree_np['cur_node'];
}
unset($tree_dt['cur_node'], $tree_jj['cur_node'],
$tree_nn['cur_node'], $tree_pp['cur_node'],
$tree_aux['cur_node'], $tree_np['cur_node']);
$sub_tree = ['DT' => $tree_dt, 'JJ' => $tree_jj, 'NN' => $tree_nn,
'PRP' => $tree_pp, 'AUX' => $tree_aux, 'CC' => $cc,
'ADD_NP' => $tree_np];
return ['cur_node' => $cur_node, 'NP' => $sub_tree];
}
/**
* Takes a part-of-speech tagged phrase and pre-tree with a
* parse-from position and builds a parse tree for a verb phrase if possible
*
* @param array $tagged_phrase
* an array of pairs of the form ("token" => token_for_term,
* "tag"=> part_of_speech_tag_for_term)
* @param array $tree that consists of ["curnode" =>
* current parse position in $tagged_phrase]
* @return array has fields
* "cur_node" index of how far we parsed $tagged_phrase
* "VP" a subarray with possible fields
* "VB" with value a verb subtree
* "NP" with value an noun phrase subtree
*/
public static function parseVerbPhrase($tagged_phrase, $tree)
{
$cur_node = $tree['cur_node'];
$adverb_string = self::parseTypeList($cur_node, $tagged_phrase,
self::$adverb_type);
$tree_vb = self::parseVerb($tagged_phrase, ['cur_node' => $cur_node]);
if ($cur_node == $tree_vb['cur_node']) {
// if no verb return what started with
return $tree;
}
$cur_node = $tree_vb['cur_node'];
$add_to_adverb_string = self::parseTypeList($cur_node,
$tagged_phrase, self::$adverb_type);
if (trim($add_to_adverb_string) != 'very') {
$adverb_string .= $add_to_adverb_string;
$tree_vb['cur_node'] = $cur_node;
} else {
$tagged_phrase[$tree_vb['cur_node']]['tag'] = 'JJ';
}
$tree_np = self::parseNounPhrase($tagged_phrase,
['cur_node' => $tree_vb['cur_node']]);
$adverb_string .= self::parseTypeList($tree_np['cur_node'],
$tagged_phrase, self::$adverb_type);
if (!empty($adverb_string)) {
$tree_vb["RB"] = $adverb_string;
}
$cur_node = $tree_np['cur_node'];
if (!empty($tree_np['NP'])) {
unset($tree_vb['cur_node'], $tree_np['cur_node']);
return ['VP' => ['VB' => $tree_vb, 'NP' => $tree_np['NP']],
'cur_node' => $cur_node];
}
unset($tree_vb['cur_node']);
return ['VP' => ['VB' => $tree_vb], 'cur_node' => $cur_node];
}
/**
* Given a part-of-speeech tagged phrase array generates a parse tree
* for the phrase using a recursive descent parser.
*
* @param array $tagged_phrase
* an array of pairs of the form ("token" => token_for_term,
* "tag"=> part_of_speech_tag_for_term)
* @param $tree that consists of ["curnode" =>
* current parse position in $tagged_phrase]
* @return array used to represent a tree. The array has up to three fields
* $tree["cur_node"] index of how far we parsed our$tagged_phrase
* $tree["NP"] contains a subtree for a noun phrase
* $tree["VP"] contains a subtree for a verb phrase
*/
public static function parseWholePhrase($tagged_phrase, $tree)
{
// for example: In the dark of winter, he walked silently.
$tree_start = self::parsePrepositionalPhrases($tagged_phrase,
["cur_node" => $tree['cur_node']]);
$cur_node = empty($tree_start['cur_node']) ? $tree['cur_node'] :
$tree_start['cur_node'];
unset($tree_start['cur_node']);
//cur_node is the index in tagged_phrase we've parse to so far
$tree_np = self::parseNounPhrase($tagged_phrase,
["cur_node" => $cur_node]);
if ($tree_np['cur_node'] == $cur_node) {
return $tree;
}
$tree_vp = self::parseVerbPhrase($tagged_phrase,
["cur_node" => $tree_np['cur_node']]);
if ($tree_np['cur_node'] == $tree_vp['cur_node']) {
return $tree;
}
$cur_node = $tree_vp['cur_node'];
unset($tree_np['cur_node'], $tree_vp['cur_node']);
if (!empty($tree_start) && !empty($tree_np['NP'])) {
$tree_np['NP']['PRP-1'] = $tree_start;
}
return ['cur_node' => $cur_node, 'NP' => $tree_np['NP'],
'VP' => $tree_vp['VP']];
}
/**
* Takes a part-of-speech tagged phrase and pre-tree with a
* parse-from position and builds a parse tree for a auxiliary clause
* if possible
*
* @param array $tagged_phrase
* an array of pairs of the form ("token" => token_for_term,
* "tag"=> part_of_speech_tag_for_term)
* @param array $tree that consists of ["cur_node" =>
* current parse position in $tagged_phrase]
* @return array has fields
* "cur_node" index of how far we parsed $tagged_phrase
*/
public static function parseAuxClause($tagged_phrase, $tree)
{
$cur_node = $tree["cur_node"];
$token = empty($tagged_phrase[$cur_node]["token"]) ? "" :
trim($tagged_phrase[$cur_node]["token"]);
if (!in_array($token, ["that", "who", "which", "because", "like",
"as"])) {
return $tree;
}
$cur_node++;
$tree_vp = self::parseVerbPhrase($tagged_phrase,
["cur_node" => $cur_node]);
if ($cur_node != $tree_vp['cur_node']) {
$cur_node = $tree_vp['cur_node'];
unset($tree_vp['cur_node']);
return ['cur_node' => $cur_node,
'IN' => $token, 'PHRASE' => $tree_vp];
}
$tree_wp = self::parseWholePhrase($tagged_phrase,
["cur_node" => $cur_node]);
if ($tree_wp['cur_node'] == $cur_node) {
return $tree;
}
$cur_node = $tree_wp['cur_node'];
unset($tree_wp['cur_node']);
return ['cur_node' => $cur_node,
'IN' => $token, 'PHRASE' => $tree_wp];
}
/**
* Takes a parse tree of a phrase and computes subject, predicate, and
* object arrays. Each of these array consists of two components CONCISE and
* RAW, CONCISE corresponding to something more similar to the words in the
* original phrase and RAW to the case where extraneous words have been
* removed
*
* @param are $tree a parse tree for a sentence
* @return array triplet array
*/
public static function extractTripletsParseTree($tree)
{
$triplets = [];
$triplets['subject'] = self::extractSubjectParseTree($tree);
$triplets['predicate'] = self::extractPredicateParseTree($tree);
$triplets['object'] = self::extractObjectParseTree($tree);
return $triplets;
}
/**
* Scans a word list for phrases. For phrases found generate
* a list of question and answer pairs at two levels of granularity:
* CONCISE (using all terms in original phrase) and RAW (removing
* (adjectives, etc).
*
* @param array $word_and_phrase_list of statements
* @return array with two fields: QUESTION_LIST consisting of triplets
* (SUBJECT, PREDICATES, OBJECT) where one of the components has been
* replaced with a question marker.
*/
public static function extractTripletsPhrases($word_and_phrase_list)
{
$triplets_list = [];
$question_list = [];
$question_answer_list = [];
$word_and_phrase_list = array_filter($word_and_phrase_list,
function ($key) {
return str_word_count($key) >= C\PHRASE_THRESHOLD;
}, \ARRAY_FILTER_USE_KEY );
$triplet_types = ['CONCISE', 'RAW'];
foreach ($word_and_phrase_list as $word_and_phrase => $position_list) {
$word_and_phrase = self::compressSentence($word_and_phrase);
// strip parentheticals
$word_and_phrase = preg_replace("/[\{\[\(][^\}\]\)]+[\}\]\)]/u",
"", $word_and_phrase);
$tagged_phrase = self::tagTokenizePartOfSpeech($word_and_phrase);
$parse_tree = self::parseWholePhrase($tagged_phrase,
['cur_node' => 0]);
$triplets = self::extractTripletsParseTree($parse_tree);
$extracted_triplets = self::rearrangeTripletsByType($triplets);
foreach ($triplet_types as $type) {
if (!empty($extracted_triplets[$type])) {
$triplets = $extracted_triplets[$type];
$questions = $triplets['QUESTION_LIST'];
foreach ($questions as $question) {
$question_list[$question] = $position_list;
}
$question_answer_list = array_merge($question_answer_list,
$triplets['QUESTION_ANSWER_LIST']);
}
}
}
$out_triplets['QUESTION_LIST'] = $question_list;
$out_triplets['QUESTION_ANSWER_LIST'] = $question_answer_list;
return $out_triplets;
}
/**
* Takes phrase tree $tree and a part-of-speech $pos returns
* the deepest $pos only path in tree.
*
* @param array $tree phrase to extract type from
* @param string $pos the part of speech to extract
* @return string the label of deepest $pos only path in $tree
*/
public static function extractDeepestSpeechPartPhrase($tree, $pos)
{
$extract = "";
if (!empty($tree[$pos])) {
$extract = self::extractDeepestSpeechPartPhrase($tree[$pos], $pos);
}
if (!$extract && !empty($tree[$pos]) && !empty($tree[$pos][$pos])) {
$extract = $tree[$pos][$pos];
}
return $extract;
}
/**
* Takes a parse tree of a phrase or statement and returns an array
* with two fields CONCISE and RAW the former having the object of
* the original phrase (as a string) the latter having the importart
* parts of the object
*
* @param array $tree representation of a parse tree of a phrase
* @return array with two fields CONCISE and RAW as described above
*/
public static function extractObjectParseTree($tree)
{
$object = [];
if (!empty($tree['VP'])) {
$tree_vp = $tree['VP'];
if (!empty($tree_vp['NP'])) {
$nb = $tree_vp['NP'];
$object['CONCISE'] = self::extractDeepestSpeechPartPhrase($nb,
"NN");
$raw_object = "";
$it = new \RecursiveIteratorIterator(
new \RecursiveArrayIterator($nb));
foreach ($it as $v) {
$raw_object .= $v . " ";
}
$object['RAW'] = $raw_object;
} else {
$object['CONCISE'] = "";
$object['RAW'] = "";
}
} else {
$object['CONCISE'] = "";
$object['RAW'] = "";
}
return $object;
}
/**
* Takes a parse tree of a phrase or statement and returns an array
* with two fields CONCISE and RAW the former having the predicate of
* the original phrase (as a string) the latter having the importart
* parts of the predicate
*
* @param array $tree representation of a parse tree of a phrase
* @return array with two fields CONCISE and RAW as described above
*/
public static function extractPredicateParseTree($tree)
{
$predicate = [];
if (!empty($tree['VP'])) {
$tree_vp = $tree['VP'];
$predicate['CONCISE'] = self::extractDeepestSpeechPartPhrase(
$tree_vp, "VB");
$raw_predicate = "";
if (!empty($tree_vp['VB'])) {
$tree_vb = $tree_vp['VB'];
$it = new \RecursiveIteratorIterator(
new \RecursiveArrayIterator($tree_vb));
foreach ($it as $v) {
$raw_predicate .= $v . " ";
}
$predicate['RAW'] = $raw_predicate;
}
} else {
$predicate['CONCISE'] = "";
$predicate['RAW'] = "";
}
return $predicate;
}
/**
* Takes a parse tree of a phrase or statement and returns an array
* with two fields CONCISE and RAW the former having the subject of
* the original phrase (as a string) the latter having the importart
* parts of the subject
*
* @param array $tree representation of a parse tree of a phrase
* @return array with two fields CONCISE and RAW as described above
*/
public static function extractSubjectParseTree($tree)
{
$subject = [];
if (!empty($tree['NP'])) {
$subject['CONCISE'] = self::extractDeepestSpeechPartPhrase(
$tree['NP'], "NN");
$raw_subject = "";
$it = new \RecursiveIteratorIterator(
new \RecursiveArrayIterator($tree['NP']));
foreach ($it as $v) {
$raw_subject .= $v . " ";
}
$subject['RAW'] = $raw_subject;
} else {
$subject['CONCISE'] = "";
$subject['RAW'] = "";
}
return $subject;
}
/**
* Takes tagged question string starts with Who
* and returns question triplet from the question string
*
* @param string $tagged_question part-of-speech tagged question
* @param int $index current index in statement
* @return array parsed triplet
*/
public static function parseWhoQuestion($tagged_question, $index)
{
$generated_questions = [];
$tree = ["cur_node" => $index];
$tree['NP'] = "WHO";
$triplets = [];
$tree_vp = self::parseVerbPhrase($tagged_question, $tree);
$triplets['predicate'] = self::extractPredicateParseTree(
$tree_vp);
$triplets['object'] = self::extractObjectParseTree(
$tree_vp);
$triplet_types = ['CONCISE', 'RAW'];
foreach ($triplet_types as $type) {
if (!empty($triplets['object'][$type])
&& !empty($triplets['predicate'][$type])) {
$generated_questions[$type][] =
trim($triplets['object'][$type]) .
" " . trim($triplets['predicate'][$type]) . " " .
self::$question_token;
$generated_questions[$type][] = self::$question_token .
" " . trim($triplets['predicate'][$type]) .
" " . trim($triplets['object'][$type]);
}
}
return $generated_questions;
}
/**
* Takes tagged question string starts with Wh+ except Who
* and returns question triplet from the question string
* Unlike the WHO case, here we assume there is an auxliary verb
* followed by a noun phrase then the rest of the verb phrase. For example,
* Where is soccer played?
*
* @param string $tagged_question part-of-speech tagged question
* @param $index current index in statement
* @return array parsed triplet suitable for query look-up
*/
public static function parseWHPlusQuestion($tagged_question, $index)
{
$generated_questions = [];
$aux_verb = "";
while (isset($tagged_question[$index]) &&
in_array(trim($tagged_question[$index]['tag']),
self::$verb_type)) {
$token = trim($tagged_question[$index]['token']);
$aux_verb .= " " . $token;
$index++;
}
$tree = ["cur_node" => $index];
$tree['NP'] = "WHPlus";
$triplets = [];
$tree_np = self::parseNounPhrase($tagged_question, $tree);
$triplets['subject'] = self::extractSubjectParseTree($tree_np);
$tree_vp = self::parseVerbPhrase($tagged_question, $tree_np);
$triplets['predicate'] = self::extractPredicateParseTree($tree_vp);
if (!empty($aux_verb)) {
if (!isset($triplets['predicate']['RAW'])) {
$triplets['predicate']['RAW'] = "";
}
$triplets['predicate']['RAW'] = trim($aux_verb) .
" " . $triplets['predicate']['RAW'];
}
$triplet_types = ['CONCISE', 'RAW'];
foreach ($triplet_types as $type) {
if (!empty($triplets['subject'][$type])&&
!empty($triplets['predicate'][$type])) {
$generated_questions[$type][] =
trim($triplets['subject'][$type]) .
" " . trim($triplets['predicate'][$type]) .
" " . self::$question_token;
$generated_questions[$type][] = self::$question_token .
" " . trim($triplets['predicate'][$type]) .
" " . trim($triplets['subject'][$type]);
}
}
return $generated_questions;
}
/**
* Takes any question started with WH question and returns the
* triplet from the question
*
* @param string $question question to parse
* @return array question triplet
*/
public static function questionParser($question)
{
$question = preg_replace("/how\s+to/", "howto", $question);
$tagged_question = self::tagTokenizePartOfSpeech($question);
$generated_questions = [];
if (isset($tagged_question[0])) {
if (in_array(trim($tagged_question[0]['tag']),
["WRB", "WP"])) {
$token = strtoupper(trim($tagged_question[0]['token']));
if ($token == "WHO") {
$generated_questions = self::parseWhoQuestion(
$tagged_question, 1);
} else if (in_array($token, ["WHERE", "WHEN", "WHAT",
"HOW", "HOWTO"])) {
$generated_questions = self::parseWHPlusQuestion(
$tagged_question, 1);
}
}
}
return $generated_questions;
}
/**
* Takes a triplets array with subject, predicate, object fields with
* CONCISE, RAW subfields and produces a triplits with $type subfield (where
* $type is one of CONCISE and RAW) and with subject, predicate, object,
* and QUESTION_ANSWER_LIST subfields
*
* @param array $sub_pred_obj_triplets in format described above
* @param string $type either CONCISE or RAW
* @return array $triplets in format described above
*/
public static function extractTripletByType($sub_pred_obj_triplets, $type)
{
$triplets = [];
if (!empty($sub_pred_obj_triplets['subject'][$type])
&& !empty($sub_pred_obj_triplets['predicate'][$type])
&& !empty($sub_pred_obj_triplets['object'][$type])) {
$question_answer_triplets = [];
$sentence = [ trim($sub_pred_obj_triplets['subject'][$type]),
trim($sub_pred_obj_triplets['predicate'][$type]),
trim($sub_pred_obj_triplets['object'][$type])];
$question_triplets = [];
for ($j = 0; $j < 2; $j++) {
if ($j == 1 && in_array($sentence[1], ['is', 'was'])) {
$tmp = $sentence[2];
$sentence[2] = $sentence[0];
$sentence[0] = $tmp;
} else if ($j == 1) {
break;
}
for ($i = 0; $i < 3; $i++) {
$q_sentence = $sentence;
$q_sentence[$i] = self::$question_token;
$q_sentence_string = implode(" ", $q_sentence);
$q_sentence_string = self::stemPhrase($q_sentence_string);
$question_triplets[] = $q_sentence_string;
$question_answer_triplets[$q_sentence_string] =
preg_replace('/\s+/u', ' ',$sentence[$i]);
}
}
$triplets['QUESTION_LIST'] = $question_triplets;
$triplets['QUESTION_ANSWER_LIST'] = $question_answer_triplets;
}
return $triplets;
}
/**
* Given an English phrase produces a phrase where each of the terms has
* been stemmed
*
* @param string $phrase phrase to stem
* @return string in which each term has been stemmed according to the
* English stemmer
*/
private static function stemPhrase($phrase)
{
$terms = mb_split("[[:space:]]", $phrase);
if (empty($terms)) {
return "";
}
$stemmed_phrase = "";
$space = "";
foreach ($terms as $term) {
if (trim($term) == "") {
continue;
}
$stemmed_phrase .= $space . self::stem($term);
$space = " ";
}
return $stemmed_phrase;
}
// private methods for stemming
/**
* Checks to see if the ith character in the buffer is a consonant
*
* @param int $i the character to check
* @return if the ith character is a constant
*/
private static function cons($i)
{
return match (self::$buffer[$i]) {
'a', 'e', 'i', 'o', 'u' => false,
'y' => ($i == 0) ? true : !self::cons($i - 1),
default => true,
};
}
/**
* m() measures the number of consonant sequences between 0 and j. if c is
* a consonant sequence and v a vowel sequence, and [.] indicates arbitrary
* presence,
* <pre>
* [c][v] gives 0
* [c]vc[v] gives 1
* [c]vcvc[v] gives 2
* [c]vcvcvc[v] gives 3
* ....
* </pre>
* @return int measure (number of [c][v][c] repetitions before $j) of
* the word stem currently in self::$b[0..self::$j], used by the
* Porter stemmer's vowel-consonant pattern rules
*/
private static function m()
{
$n = 0;
$i = 0;
while(true) {
if ($i > self::$j) return $n;
if (!self::cons($i)) break;
$i++;
}
$i++;
while(true) {
while(true) {
if ($i > self::$j) return $n;
if (self::cons($i)) break;
$i++;
}
$i++;
$n++;
while(true)
{
if ($i > self::$j) return $n;
if (!self::cons($i)) break;
$i++;
}
$i++;
}
}
/**
* Checks if 0,...$j contains a vowel
*
* @return bool whether it does not
*/
private static function vowelinstem()
{
for ($i = 0; $i <= self::$j; $i++) {
if (!self::cons($i)) return true;
}
return false;
}
/**
* Checks if $j,($j-1) contain a double consonant.
*
* @param int $j position to check in buffer for double consonant
* @return bool if it does or not
*/
private static function doublec($j)
{
if ($j < 1) { return false; }
if (self::$buffer[$j] != self::$buffer[$j - 1]) { return false; }
return self::cons($j);
}
/**
* Checks whether the letters at the indices $i-2, $i-1, $i in the buffer
* have the form consonant - vowel - consonant and also if the second c is
* not w,x or y. this is used when trying to restore an e at the end of a
* short word. e.g.
*<pre>
* cav(e), lov(e), hop(e), crim(e), but
* snow, box, tray.
*</pre>
* @param int $i position to check in buffer for consonant-vowel-consonant
* @return bool whether the letters at indices have the given form
*/
private static function cvc($i)
{
if ($i < 2 || !self::cons($i) || self::cons($i - 1) ||
!self::cons($i - 2)) return false;
$ch = self::$buffer[$i];
if ($ch == 'w' || $ch == 'x' || $ch == 'y') return false;
return true;
}
/**
* Checks if the buffer currently ends with the string $s
*
* @param string $s string to use for check
* @return bool whether buffer currently ends with $s
*/
private static function ends($s)
{
$len = strlen($s);
$loc = self::$k - $len + 1;
if ($loc < 0 ||
substr_compare(self::$buffer, $s, $loc, $len) != 0) {
return false;
}
self::$j = self::$k - $len;
return true;
}
/**
* setto($s) sets (j+1),...k to the characters in the string $s,
* readjusting k.
*
* @param string $s string to modify the end of buffer with
*/
private static function setto($s)
{
$len = strlen($s);
$loc = self::$j + 1;
self::$buffer = substr_replace(self::$buffer, $s, $loc, $len);
self::$k = self::$j + $len;
}
/**
* Sets the ending in the buffer to $s if the number of consonant sequences
* between $k and $j is positive.
*
* @param string $s what to change the suffix to
*/
private static function r($s)
{
if (self::m() > 0) self::setto($s);
}
/** step1ab() gets rid of plurals and -ed or -ing. e.g.
* <pre>
* caresses -> caress
* ponies -> poni
* ties -> ti
* caress -> caress
* cats -> cat
*
* feed -> feed
* agreed -> agree
* disabled -> disable
*
* matting -> mat
* mating -> mate
* meeting -> meet
* milling -> mill
* messing -> mess
*
* meetings -> meet
* </pre>
*/
private static function step1ab()
{
if (self::$buffer[self::$k] == 's') {
if (self::ends("sses")) {
self::$k -= 2;
} else if (self::ends("ies")) {
self::setto("i");
} else if (self::$buffer[self::$k - 1] != 's') {
self::$k--;
}
}
if (self::ends("eed")) {
if (self::m() > 0) self::$k--;
} else if ((self::ends("ed") || self::ends("ing")) &&
self::vowelinstem()) {
self::$k = self::$j;
if (self::ends("at")) {
self::setto("ate");
} else if (self::ends("bl")) {
self::setto("ble");
} else if (self::ends("iz")) {
self::setto("ize");
} else if (self::doublec(self::$k)) {
self::$k--;
$ch = self::$buffer[self::$k];
if ($ch == 'l' || $ch == 's' || $ch == 'z') self::$k++;
} else if (self::m() == 1 && self::cvc(self::$k)) {
self::setto("e");
}
}
}
/**
* step1c() turns terminal y to i when there is another vowel in the stem.
*/
private static function step1c()
{
if (self::ends("y") && self::vowelinstem()) {
self::$buffer[self::$k] = 'i';
}
}
/**
* step2() maps double suffiXes to single ones. so -ization ( = -ize plus
* -ation) maps to -ize etc. Note that the string before the suffix must
* give m() > 0.
*/
private static function step2()
{
if (self::$k < 1) return;
switch (self::$buffer[self::$k - 1]) {
case 'a':
if (self::ends("ational")) { self::r("ate"); break; }
if (self::ends("tional")) { self::r("tion"); break; }
break;
case 'c':
if (self::ends("enci")) { self::r("ence"); break; }
if (self::ends("anci")) { self::r("ance"); break; }
break;
case 'e':
if (self::ends("izer")) { self::r("ize"); break; }
break;
case 'l':
if (self::ends("abli")) { self::r("able"); break; }
if (self::ends("alli")) { self::r("al"); break; }
if (self::ends("entli")) { self::r("ent"); break; }
if (self::ends("eli")) { self::r("e"); break; }
if (self::ends("ousli")) { self::r("ous"); break; }
break;
case 'o':
if (self::ends("ization")) { self::r("ize"); break; }
if (self::ends("ation")) { self::r("ate"); break; }
if (self::ends("ator")) { self::r("ate"); break; }
break;
case 's':
if (self::ends("alism")) { self::r("al"); break; }
if (self::ends("iveness")) { self::r("ive"); break; }
if (self::ends("fulness")) { self::r("ful"); break; }
if (self::ends("ousness")) { self::r("ous"); break; }
break;
case 't':
if (self::ends("aliti")) { self::r("al"); break; }
if (self::ends("iviti")) { self::r("ive"); break; }
if (self::ends("biliti")) { self::r("ble"); break; }
break;
}
}
/**
* step3() deals with -ic-, -full, -ness etc. similar strategy to step2.
*/
private static function step3()
{
switch (self::$buffer[self::$k]) {
case 'e':
if (self::ends("icate")) { self::r("ic"); break; }
if (self::ends("ative")) { self::r(""); break; }
if (self::ends("alize")) { self::r("al"); break; }
break;
case 'i':
if (self::ends("iciti")) { self::r("ic"); break; }
break;
case 'l':
if (self::ends("ical")) { self::r("ic"); break; }
if (self::ends("ful")) { self::r(""); break; }
break;
case 's':
if (self::ends("ness")) { self::r(""); break; }
break;
}
}
/**
* step4() takes off -ant, -ence etc., in context <c>vcvc<v>.
*/
private static function step4()
{
if (self::$k < 1) { return; }
switch (self::$buffer[self::$k - 1]) {
case 'a':
if (self::ends("al")) { break; }
return;
case 'c':
if (self::ends("ance")) { break; }
if (self::ends("ence")) { break; }
return;
case 'e':
if (self::ends("er")) break;
return;
case 'i':
if (self::ends("ic")) break;
return;
case 'l':
if (self::ends("able")) break;
if (self::ends("ible")) break;
return;
case 'n':
if (self::ends("ant")) break;
if (self::ends("ement")) break;
if (self::ends("ment")) break;
if (self::ends("ent")) break;
return;
case 'o':
if (self::ends("ion") && self::$j >= 0 &&
(self::$buffer[self::$j] == 's' ||
self::$buffer[self::$j] == 't')) break;
if (self::ends("ou")) break;
return;
/* takes care of -ous */
case 's':
if (self::ends("ism")) break;
return;
case 't':
if (self::ends("ate")) break;
if (self::ends("iti")) break;
return;
case 'u':
if (self::ends("ous")) break;
return;
case 'v':
if (self::ends("ive")) break;
return;
case 'z':
if (self::ends("ize")) break;
return;
default:
return;
}
if (self::m() > 1) self::$k = self::$j;
}
/** step5() removes a final -e if m() > 1, and changes -ll to -l if
* m() > 1.
*/
private static function step5()
{
self::$j = self::$k;
if (self::$buffer[self::$k] == 'e') {
$a = self::m();
if ($a > 1 || $a == 1 && !self::cvc(self::$k - 1)) self::$k--;
}
if (self::$buffer[self::$k] == 'l' &&
self::doublec(self::$k) && self::m() > 1) self::$k--;
}
//private methods for part of speech tagging
/**
* Takes an array of pairs (token, tag) that came from phrase
* and builds a new phrase where terms look like token~tag.
*
* @param array $tagged_tokens array pairs as might come from tagTokenize
* @param bool $with_tokens whether to include the terms and the tags
* in the output string or just the part of speech tags
* @return string $tagged_phrase a phrase with terms in the format token~tag
* ($with_token == true) or space separated tags (!$with_token).
*/
private static function taggedPartOfSpeechTokensToString($tagged_tokens,
$with_tokens = true)
{
$tagged_phrase = "";
$simplified_parts_of_speech = [
"NN" => "NN", "NNS" => "NN", "NNP" => "NN", "NNPS" => "NN",
"PRP" => "NN", 'PRP$' => "NN", "WP" => "NN",
"VB" => "VB", "VBD" => "VB", "VBN" => "VB", "VBP" => "VB",
"VBZ" => "VB",
"JJ" => "AJ", "JJR" => "AJ", "JJS" => "AJ",
"RB" => "AV", "RBR" => "AV", "RBS" => "AV", "WRB" => "AV"
];
foreach ($tagged_tokens as $t) {
$tag = trim($t['tag']);
$tag = (isset($simplified_parts_of_speech[$tag])) ?
$simplified_parts_of_speech[$tag] : $tag;
$token = ($with_tokens) ? $t['token'] . "~" : "";
$tagged_phrase .= $token . $tag . " ";
}
return $tagged_phrase;
}
}
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