In a case-insensitive thesaurus, terms are stored in all-uppercase, regardless of the case in which they were originally entered.
The ctxload program loads a thesaurus in case-insensitive mode by default.
When creating a thesaurus with either CTX_THES.CREATE_THESAURUS or CTX_THES.IMPORT_THESAURUS, the thesaurus is created as case-insensitive by default.
In addition, when a case-insensitive thesaurus is specified in a query, the query terms are converted to all-uppercase for thesaurus lookup. As a result, Oracle Text is unable to distinguish between terms that have different meanings when they are in mixed-case.
For example, a case-insensitive thesaurus is created with different entries for the two distinct meanings of the term TURKEY (the country or the type of bird). Using the thesaurus, a query for either Turkey or turkey is converted to TURKEY for thesaurus lookup and then expanded to include all the entries associated with both meanings.
The "ctxload Utility"