org.apache.lucene.analysis.pt
Class RSLPStemmerBase

java.lang.Object
  org.apache.lucene.analysis.pt.RSLPStemmerBase

Direct Known Subclasses:

GalicianMinimalStemmer, GalicianStemmer, PortugueseMinimalStemmer, PortugueseStemmer

public abstract class RSLPStemmerBase
extends Object

Base class for stemmers that use a set of RSLP-like stemming steps.

RSLP (Removedor de Sufixos da Lingua Portuguesa) is an algorithm designed originally for stemming the Portuguese language, described in the paper A Stemming Algorithm for the Portuguese Language, Orengo et. al.

Since this time a plural-only modification (RSLP-S) as well as a modification for the Galician language have been implemented. This class parses a configuration file that describes RSLPStemmerBase.Steps, where each Step contains a set of RSLPStemmerBase.Rules.

The general rule format is:

{ "suffix", N, "replacement", { "exception1", "exception2", ...}}

where:

• suffix is the suffix to be removed (such as "inho").
• N is the min stem size, where stem is defined as the candidate stem after removing the suffix (but before appending the replacement!)
• replacement is an optimal string to append after removing the suffix. This can be the empty string.
• exceptions is an optional list of exceptions, patterns that should not be stemmed. These patterns can be specified as whole word or suffix (ends-with) patterns, depending upon the exceptions format flag in the step header.

A step is an ordered list of rules, with a structure in this format:

{ "name", N, B, { "cond1", "cond2", ... } ... rules ... };

where:

• name is a name for the step (such as "Plural").
• N is the min word size. Words that are less than this length bypass the step completely, as an optimization. Note: N can be zero, in this case this implementation will automatically calculate the appropriate value from the underlying rules.
• B is a "boolean" flag specifying how exceptions in the rules are matched. A value of 1 indicates whole-word pattern matching, a value of 0 indicates that exceptions are actually suffixes and should be matched with ends-with.
• conds are an optional list of conditions to enter the step at all. If the list is non-empty, then a word must end with one of these conditions or it will bypass the step completely as an optimization.

See Also:

RSLP description

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

Nested Class Summary

protected static class	RSLPStemmerBase.Rule A basic rule, with no exceptions.
protected static class	RSLPStemmerBase.RuleWithSetExceptions A rule with a set of whole-word exceptions.
protected static class	RSLPStemmerBase.RuleWithSuffixExceptions A rule with a set of exceptional suffixes.
protected static class	RSLPStemmerBase.Step A step containing a list of rules.

Constructor Summary

RSLPStemmerBase()

Method Summary

protected static Map<String,RSLPStemmerBase.Step>

parse(Class<? extends RSLPStemmerBase> clazz, String resource) Parse a resource file into an RSLP stemmer description.

Methods inherited from class java.lang.Object

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

Constructor Detail

RSLPStemmerBase

public RSLPStemmerBase()

Method Detail

parse

protected static Map<String,RSLPStemmerBase.Step> parse(Class<? extends RSLPStemmerBase> clazz,
                                                        String resource)

Parse a resource file into an RSLP stemmer description.

Returns:

a Map containing the named Steps in this description.