it.unimi.di.mg4j.index
Interface TermProcessor

All Superinterfaces:

FlyweightPrototype<TermProcessor>, Serializable

All Known Implementing Classes:

AbstractSnowballTermProcessor, DanishStemmer, DowncaseTermProcessor, DutchStemmer, EnglishStemmer, FinnishStemmer, FrenchStemmer, German2Stemmer, GermanStemmer, HungarianStemmer, ItalianStemmer, KraaijPohlmannStemmer, LovinsStemmer, NorwegianStemmer, NullTermProcessor, PorterStemmer, PortugueseStemmer, SpanishStemmer, SwedishStemmer

public interface TermProcessor
extends Serializable, FlyweightPrototype<TermProcessor>

A term processor, implementing term/prefix transformation and possibly term/prefix filtering.

Index contruction requires sometimes modifications of the given terms: downcasing, stemming, and so on. The same transformation must be applied to terms in a query. This interface provides a uniform way to perform arbitrary term transformations.

Index construction requires also term filtering: processTerm(MutableString) may return false, indicating that the term should not be processed at all (e.g., because it is a stopword).

Additionally, the method processPrefix(MutableString) may process analogously a prefix (used for prefix queries).

Implementation are encouraged to expose a singleton, when possible, by means of the static factory method getInstance(). Warning: implementations of this class are not required to be thread-safe, but they provide flyweight copies. The copy() method is strengthened so to return a instance of this class.

This interface was originally suggested by Fabien Campagne.

Method Summary

TermProcessor	copy()
boolean	processPrefix(MutableString prefix) Processes the given prefix, leaving the result in the same mutable string.
boolean	processTerm(MutableString term) Processes the given term, leaving the result in the same mutable string.

Method Detail

processTerm

boolean processTerm(MutableString term)

Processes the given term, leaving the result in the same mutable string.

Parameters:

term - a mutable string containing the term to be processed, or null.

Returns:

true if the term is not null and should be indexed, false otherwise.

processPrefix

boolean processPrefix(MutableString prefix)

Processes the given prefix, leaving the result in the same mutable string.

This method is not used during the indexing phase, but rather at query time. If the user wants to specify a prefix query, it is sometimes necessary to transform the prefix (e.g., DowncaseTermProcessor.processPrefix(MutableString) downcasing it).

It is of course unlikely that this method returns false, as it is usually not possible to foresee which are the prefixes of indexable words. In case no natural transformation applies, this method should leave its argument unchanged.

Parameters:

prefix - a mutable string containing a prefix to be processed, or null.

Returns:

true if the prefix is not null and there might be an indexed word starting with prefix, false otherwise.

copy

TermProcessor copy()

Specified by:

copy in interface FlyweightPrototype<TermProcessor>