Base-Letter Conversion

Besides alternative spelling, Oracle Text also handles base-letter conversions. With base-letter conversions enabled, letters with umlauts, acute accents, cedillas, and the like are converted to their basic forms for indexing, so fiancé is indexed both as fiancé and as fiance, and a query of fiancé returns documents containing either form.

To enable base-letter conversions, set the BASIC_LEXER attribute BASE_LETTER to YES. See “BASIC_LEXER” for more information.

When Alternate Spelling is also enabled, Base-Letter Conversion may need to be overridden to prevent unexpected results. See “Overriding Alternative Spelling Features” for more information.

Generic Versus Language-Specific Base-Letter Conversions

The BASE_LETTER_TYPE attribute affects the way base-letter conversions take place. It has two possible values: GENERIC or SPECIFIC.

The GENERIC value is the default and specifies that base letter transformation uses one transformation table that applies to all languages.

The SPECIFIC value means that a base-letter transformation that has been specifically defined for your language will be used. This enables you to use accent-sensitive searches for words in your own language, while ignoring accents that are from other languages.

For example, both the GENERIC and the Spanish SPECIFIC tables will transform é into e. However, they treat the letter ñ distinctly. The GENERIC table treats ñ as an n with an accent (actually, a tilde), and so transforms ñ to n. The Spanish SPECIFIC table treats ñ as a separate letter of the alphabet, and thus does not transform it.