Stoplists

Stoplists identify the words in your language that are not to be indexed. In English, you can also identify stopthemes that are not to be indexed. By default, the system indexes text using the system-supplied stoplist that corresponds to your database language.

Oracle Text provides default stoplists for most languages including English, French, German, Spanish, Dutch, and Danish. These default stoplists contain only stopwords.

See Also: For more information about the supplied default stoplists, see Appendix D, "Supplied Stoplists".

Multi-Language Stoplists

You can create multi-language stoplists to hold language-specific stopwords. A multi-language stoplist is useful when you use the MULTI_LEXER to index a table that contains documents in different languages, such as English, German, and Japanese.

To create a multi-language stoplist, use the CTX_DLL.CREATE_STOPLIST procedure and specify a stoplist type of MULTI_STOPLIST. You add language specific stopwords with CTX_DDL.ADD_STOPWORD.

At indexing time, the language column of each document is examined, and only the stopwords for that language are eliminated. At query time, the session language setting determines the active stopwords, like it determines the active lexer when using the multi-lexer.

Creating Stoplists

You can create your own stoplists using the CTX_DLL.CREATE_STOPLIST procedure. With this procedure you can create a BASIC_STOPLIST for single language stoplist, or you can create a MULTI_STOPLIST for a multi-language stoplist.

When you create your own stoplist, you must specify it in the parameter clause of CREATE INDEX.

Modifying the Default Stoplist

The default stoplist is always named CTXSYS.DEFAULT_STOPLIST. You can use the following procedures to modify this stoplist:

• CTX_DDL.ADD_STOPWORD

• CTX_DDL.REMOVE_STOPWORD

• CTX_DDL.ADD_STOPTHEME

• CTX_DDL.ADD_STOPCLASS

When you modify CTXSYS.DEFAULT_STOPLIST with the CTX_DDL package, you must re-create your index for the changes to take effect.

Dynamic Addition of Stopwords

You can add stopwords dynamically to a default or custom stoplist with ALTER INDEX. When you add a stopword dynamically, you need not re-index, because the word immediately becomes a stopword and is removed from the index.

Note: Even though you can dynamically add stopwords to an index, you cannot dynamically remove stopwords. To remove a stopword, you must use CTX_DDL.REMOVE_STOPWORD, drop your index and recreate it.

See Also: ALTER INDEX in Chapter 1, "SQL Statements and Operators".