Overriding Alternative Spelling Features

Even when alternative spelling features have been specified by lexer preference, it is possible to override them.

You can override base-letter conversion when Alternate Spelling is used, to prevent characters with alternate spelling forms, such as ü, ö, and ä, from also being transformed to the base letter forms.

Overriding Base-Letter Transformations with Alternate Spelling

Transformations caused by turning on alternate_spelling are performed before those of base_letter, which can sometimes cause unexpected results when both are enabled.

When Alternate Spelling is enabled, Oracle Text converts two-letter forms to single-letter forms (for example, ue to ü), so that words can be searched in both their base and alternate forms. Therefore, with Alternate Spelling enabled, a search for Schoen will return documents with both Schoen and Schön.

However, when Base-letter Transformation is also enabled, the ü in Schlüssel is transformed into a u, producing the non-existent word (in German, anyway) Schlussel, and the word is indexed in all three forms.

To prevent this secondary conversion, set the OVERRIDE_BASE_LETTER attribute to TRUE.

OVERRIDE_BASE_LETTER only affects letters with umlauts; accented letters, for example, are still transformed into their base forms.

For more on BASE_LETTER, see “Base-Letter Conversion”.