Class RSLPStemmerBase

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 RSLPStemmerBase.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 ... };

• 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.