Package org.apache.lucene.analysis.miscellaneous

Class ScandinavianFoldingFilter

  • All Implemented Interfaces:
    Closeable, AutoCloseable
    public final class ScandinavianFoldingFilter
extends TokenFilter
    This filter folds Scandinavian characters åÅäæÄÆ->a and öÖøØ->o. It also discriminate against use of double vowels aa, ae, ao, oe and oo, leaving just the first one.

    It's a semantically more destructive solution than ScandinavianNormalizationFilter but can in addition help with matching raksmorgas as räksmörgås.

    blåbærsyltetøj == blåbärsyltetöj == blaabaarsyltetoej == blabarsyltetoj räksmörgås == ræksmørgås == ræksmörgaos == raeksmoergaas == raksmorgas

    Background: Swedish åäö are in fact the same letters as Norwegian and Danish åæø and thus interchangeable when used between these languages. They are however folded differently when people type them on a keyboard lacking these characters.

    In that situation almost all Swedish people use a, a, o instead of å, ä, ö.

    Norwegians and Danes on the other hand usually type aa, ae and oe instead of å, æ and ø. Some do however use a, a, o, oo, ao and sometimes permutations of everything above.

    This filter solves that mismatch problem, but might also cause new.

    See Also:
    ScandinavianNormalizationFilter