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Rework word set computation

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Switch from an recursive algorithm for computing the word sets
to an iterative one that benefits from caching intermediate
results. This considerably reduces the amount of memory needed,
so that the depth restriction can be dropped. To ensure that
the number of word sets remains manageable, only sets up to
a certain length are accepted and only a certain number of
total word sets. If word sets need to be dropped, we drop
the ones with more words per word set first.

To further reduce the number of potential word sets, the valid
tokens are looked up first and then only word sets containing
valid tokens are computed.

Fixes #1403, #1404 and #654.
This commit is contained in:
Sarah Hoffmann
2019-06-29 18:22:31 +02:00
parent 09e7f0d013
commit 38a99856c0
4 changed files with 143 additions and 46 deletions
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104
lib/Phrase.php
View File

@@ -9,7 +9,8 @@ namespace Nominatim;
*/
class Phrase
{
const MAX_DEPTH = 7;
public const MAX_WORDSET_LEN = 20;
public const MAX_WORDSETS = 100;
// Complete phrase as a string.
private $sPhrase;
@@ -20,13 +21,24 @@ class Phrase
// Possible segmentations of the phrase.
private $aWordSets;
public static function cmpByArraylen($aA, $aB)
{
$iALen = count($aA);
$iBLen = count($aB);
if ($iALen == $iBLen) {
return 0;
}
return ($iALen < $iBLen) ? -1 : 1;
}
public function __construct($sPhrase, $sPhraseType)
{
$this->sPhrase = trim($sPhrase);
$this->sPhraseType = $sPhraseType;
$this->aWords = explode(' ', $this->sPhrase);
$this->aWordSets = $this->createWordSets($this->aWords, 0);
}
/**
@@ -60,10 +72,17 @@ class Phrase
*/
public function addTokens(&$aTokens)
{
foreach ($this->aWordSets as $aSet) {
foreach ($aSet as $sWord) {
$aTokens[' '.$sWord] = ' '.$sWord;
$aTokens[$sWord] = $sWord;
$iNumWords = count($this->aWords);
for ($i = 0; $i < $iNumWords; $i++) {
$sPhrase = $this->aWords[$i];
$aTokens[' '.$sPhrase] = ' '.$sPhrase;
$aTokens[$sPhrase] = $sPhrase;
for ($j = $i + 1; $j < $iNumWords; $j++) {
$sPhrase .= ' '.$this->aWords[$j];
$aTokens[' '.$sPhrase] = ' '.$sPhrase;
$aTokens[$sPhrase] = $sPhrase;
}
}
}
@@ -75,44 +94,59 @@ class Phrase
*/
public function invertWordSets()
{
$this->aWordSets = $this->createInverseWordSets($this->aWords, 0);
foreach ($this->aWordSets as $i => $aSet) {
$this->aWordSets[$i] = array_reverse($aSet);
}
}
private function createWordSets($aWords, $iDepth)
public function computeWordSets($oTokens)
{
$aResult = array(array(join(' ', $aWords)));
$sFirstToken = '';
if ($iDepth < Phrase::MAX_DEPTH) {
while (count($aWords) > 1) {
$sWord = array_shift($aWords);
$sFirstToken .= ($sFirstToken?' ':'').$sWord;
$aRest = $this->createWordSets($aWords, $iDepth + 1);
foreach ($aRest as $aSet) {
$aResult[] = array_merge(array($sFirstToken), $aSet);
$iNumWords = count($this->aWords);
// Caches the word set for the partial phrase up to word i.
$aSetCache = array_fill(0, $iNumWords, array());
// Initialise first element of cache. There can only be the word.
if ($oTokens->containsAny($this->aWords[0])) {
$aSetCache[0][] = array($this->aWords[0]);
}
// Now do the next elements using what we already have.
for ($i = 1; $i < $iNumWords; $i++) {
for ($j = $i; $j > 0; $j--) {
$sPartial = $j == $i ? $this->aWords[$j] : $this->aWords[$j].' '.$sPartial;
if (!empty($aSetCache[$j - 1]) && $oTokens->containsAny($sPartial)) {
$aPartial = array($sPartial);
foreach ($aSetCache[$j - 1] as $aSet) {
if (count($aSet) < Phrase::MAX_WORDSET_LEN) {
$aSetCache[$i][] = array_merge($aSet, $aPartial);
}
}
if (count($aSetCache[$i]) > 2 * Phrase::MAX_WORDSETS) {
usort(
$aSetCache[$i],
array('\Nominatim\Phrase', 'cmpByArraylen')
);
$aSetCache[$i] = array_slice(
$aSetCache[$i],
0,
Phrase::MAX_WORDSETS
);
}
}
}
// finally the current full phrase
$sPartial = $this->aWords[0].' '.$sPartial;
if ($oTokens->containsAny($sPartial)) {
$aSetCache[$i][] = array($sPartial);
}
}
return $aResult;
$this->aWordSets = $aSetCache[$iNumWords - 1];
usort($this->aWordSets, array('\Nominatim\Phrase', 'cmpByArraylen'));
$this->aWordSets = array_slice($this->aWordSets, 0, Phrase::MAX_WORDSETS);
}
private function createInverseWordSets($aWords, $iDepth)
{
$aResult = array(array(join(' ', $aWords)));
$sFirstToken = '';
if ($iDepth < Phrase::MAX_DEPTH) {
while (count($aWords) > 1) {
$sWord = array_pop($aWords);
$sFirstToken = $sWord.($sFirstToken?' ':'').$sFirstToken;
$aRest = $this->createInverseWordSets($aWords, $iDepth + 1);
foreach ($aRest as $aSet) {
$aResult[] = array_merge(array($sFirstToken), $aSet);
}
}
}
return $aResult;
}
public function debugInfo()
{