org.apache.lucene.search.suggest.analyzing
Class FreeTextSuggester

java.lang.Object
  org.apache.lucene.search.suggest.Lookup
      org.apache.lucene.search.suggest.analyzing.FreeTextSuggester

public class FreeTextSuggester
extends Lookup

Builds an ngram model from the text sent to build(org.apache.lucene.search.suggest.InputIterator) and predicts based on the last grams-1 tokens in the request sent to lookup(java.lang.CharSequence, boolean, int). This tries to handle the "long tail" of suggestions for when the incoming query is a never before seen query string.

Likely this suggester would only be used as a fallback, when the primary suggester fails to find any suggestions.

Note that the weight for each suggestion is unused, and the suggestions are the analyzed forms (so your analysis process should normally be very "light").

This uses the stupid backoff language model to smooth scores across ngram models; see "Large language models in machine translation", http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.76.1126 for details.

From lookup(java.lang.CharSequence, boolean, int), the key of each result is the ngram token; the value is Long.MAX_VALUE * score (fixed point, cast to long). Divide by Long.MAX_VALUE to get the score back, which ranges from 0.0 to 1.0. onlyMorePopular is unused.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.search.suggest.Lookup

Lookup.LookupPriorityQueue, Lookup.LookupResult

Field Summary

static double	ALPHA The constant used for backoff smoothing; during lookup, this means that if a given trigram did not occur, and we backoff to the bigram, the overall score will be 0.4 times what the bigram model would have assigned.
static String	CODEC_NAME Codec name used in the header for the saved model.
static int	DEFAULT_GRAMS By default we use a bigram model.
static byte	DEFAULT_SEPARATOR The default character used to join multiple tokens into a single ngram token.
static int	VERSION_CURRENT Current version of the the saved model file format.
static int	VERSION_START Initial version of the the saved model file format.

Fields inherited from class org.apache.lucene.search.suggest.Lookup

CHARSEQUENCE_COMPARATOR

Constructor Summary

FreeTextSuggester(Analyzer analyzer)
Instantiate, using the provided analyzer for both indexing and lookup, using bigram model by default.

FreeTextSuggester(Analyzer indexAnalyzer, Analyzer queryAnalyzer)
Instantiate, using the provided indexing and lookup analyzers, using bigram model by default.

FreeTextSuggester(Analyzer indexAnalyzer, Analyzer queryAnalyzer, int grams)
Instantiate, using the provided indexing and lookup analyzers, with the specified model (2 = bigram, 3 = trigram, etc.).

FreeTextSuggester(Analyzer indexAnalyzer, Analyzer queryAnalyzer, int grams, byte separator)
Instantiate, using the provided indexing and lookup analyzers, and specified model (2 = bigram, 3 = trigram ,etc.).

Method Summary

void	build(InputIterator iterator) Builds up a new internal Lookup representation based on the given InputIterator.
void	build(InputIterator iterator, double ramBufferSizeMB) Build the suggest index, using up to the specified amount of temporary RAM while building.
Object	get(CharSequence key) Returns the weight associated with an input string, or null if it does not exist.
long	getCount() Get the number of entries the lookup was built with
boolean	load(DataInput input) Discard current lookup data and load it from a previously saved copy.
List<Lookup.LookupResult>	lookup(CharSequence key, boolean onlyMorePopular, int num) Look up a key and return possible completion for this key.
List<Lookup.LookupResult>	lookup(CharSequence key, int num) Retrieve suggestions.
long	sizeInBytes() Returns byte size of the underlying FST.
boolean	store(DataOutput output) Persist the constructed lookup data to a directory.

Methods inherited from class org.apache.lucene.search.suggest.Lookup

build, load, store

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

CODEC_NAME

public static final String CODEC_NAME

Codec name used in the header for the saved model.

See Also:

Constant Field Values

VERSION_START

public static final int VERSION_START

Initial version of the the saved model file format.

See Also:

Constant Field Values

VERSION_CURRENT

public static final int VERSION_CURRENT

Current version of the the saved model file format.

See Also:

Constant Field Values

DEFAULT_GRAMS

public static final int DEFAULT_GRAMS

By default we use a bigram model.

See Also:

Constant Field Values

ALPHA

public static final double ALPHA

The constant used for backoff smoothing; during lookup, this means that if a given trigram did not occur, and we backoff to the bigram, the overall score will be 0.4 times what the bigram model would have assigned.

See Also:

Constant Field Values

DEFAULT_SEPARATOR

public static final byte DEFAULT_SEPARATOR

The default character used to join multiple tokens into a single ngram token. The input tokens produced by the analyzer must not contain this character.

See Also:

Constant Field Values

Constructor Detail

FreeTextSuggester

public FreeTextSuggester(Analyzer analyzer)

Instantiate, using the provided analyzer for both indexing and lookup, using bigram model by default.

FreeTextSuggester

public FreeTextSuggester(Analyzer indexAnalyzer,
                         Analyzer queryAnalyzer)

Instantiate, using the provided indexing and lookup analyzers, using bigram model by default.

FreeTextSuggester

public FreeTextSuggester(Analyzer indexAnalyzer,
                         Analyzer queryAnalyzer,
                         int grams)

Instantiate, using the provided indexing and lookup analyzers, with the specified model (2 = bigram, 3 = trigram, etc.).

FreeTextSuggester

public FreeTextSuggester(Analyzer indexAnalyzer,
                         Analyzer queryAnalyzer,
                         int grams,
                         byte separator)

Instantiate, using the provided indexing and lookup analyzers, and specified model (2 = bigram, 3 = trigram ,etc.). The separator is passed to ShingleFilter.setTokenSeparator(java.lang.String) to join multiple tokens into a single ngram token; it must be an ascii (7-bit-clean) byte. No input tokens should have this byte, otherwise IllegalArgumentException is thrown.

Method Detail

sizeInBytes

public long sizeInBytes()

Returns byte size of the underlying FST.

Specified by:

sizeInBytes in class Lookup

Returns:

ram size of the lookup implementation in bytes

build

public void build(InputIterator iterator)
           throws IOException

Description copied from class: Lookup

Builds up a new internal Lookup representation based on the given InputIterator. The implementation might re-sort the data internally.

Specified by:

build in class Lookup

Throws:

IOException

build

public void build(InputIterator iterator,
                  double ramBufferSizeMB)
           throws IOException

Build the suggest index, using up to the specified amount of temporary RAM while building. Note that the weights for the suggestions are ignored.

Throws:

IOException

store

public boolean store(DataOutput output)
              throws IOException

Description copied from class: Lookup

Persist the constructed lookup data to a directory. Optional operation.

Specified by:

store in class Lookup

Parameters:

output - DataOutput to write the data to.

Returns:

true if successful, false if unsuccessful or not supported.

Throws:

IOException - when fatal IO error occurs.

load

public boolean load(DataInput input)
             throws IOException

Description copied from class: Lookup

Discard current lookup data and load it from a previously saved copy. Optional operation.

Specified by:

load in class Lookup

Parameters:

input - the DataInput to load the lookup data.

Returns:

true if completed successfully, false if unsuccessful or not supported.

Throws:

IOException - when fatal IO error occurs.

lookup

public List<Lookup.LookupResult> lookup(CharSequence key,
                                        boolean onlyMorePopular,
                                        int num)

Description copied from class: Lookup

Look up a key and return possible completion for this key.

Specified by:

lookup in class Lookup

Parameters:

key - lookup key. Depending on the implementation this may be a prefix, misspelling, or even infix.

onlyMorePopular - return only more popular results

num - maximum number of results to return

Returns:

a list of possible completions, with their relative weight (e.g. popularity)

getCount

public long getCount()

Description copied from class: Lookup

Get the number of entries the lookup was built with

Specified by:

getCount in class Lookup

Returns:

total number of suggester entries

lookup

public List<Lookup.LookupResult> lookup(CharSequence key,
                                        int num)
                                 throws IOException

Retrieve suggestions.

Throws:

IOException

get

public Object get(CharSequence key)

Returns the weight associated with an input string, or null if it does not exist.