ADD_SUB_LEXER

Add a sub-lexer to a multi-lexer preference. A sub-lexer identifies a language in a multi-lexer (multi-language) preference. Use a multi-lexer preference when you want to index more than one language.

Restrictions

The following restrictions apply to using CTX_DDL.ADD_SUB_LEXER:

• The invoking user must be the owner of the multi-lexer or CTXSYS.

• The lexer_name parameter must name a preference which is a multi-lexer lexer.

• A lexer for default must be defined before the multi-lexer can be used in an index.

• The sub-lexer preference owner must be the same as multi-lexer preference owner.

• The sub-lexer preference must not be a multi-lexer lexer.

• A sub-lexer preference cannot be dropped while it is being used in a multi-lexer preference.

• CTX_DDL.ADD_SUB_LEXER records only a reference. The sub-lexer values are copied at create index time to index value storage.

Syntax

CTX_DDL.ADD_SUB_LEXER(
             lexer_name in varchar2,
             language  in varchar2,
             sub_lexer in varchar2,
             alt_value in varchar2 default null
);

lexer_name

Specify the name of the multi-lexer preference.

language

Specify the NLS language name or abbreviation of the sub-lexer. For example, you can specify ENGLISH or EN for English.

The sub-lexer you specify with sub_lexer is used when the language column has a value case-insensitive equal to the NLS name of abbreviation of language.

Specify DEFAULT to assign a default sub-lexer to use when the value of the language column in the base table is null, invalid, or unmapped to a sub-lexer. The DEFAULT lexer is also used to parse stopwords.

If a sub-lexer definition for language already exists, then it is replaced by this call.

sub_lexer

Specify the name of the sub-lexer to use for this language.

alt_value

Optionally specify an alternate value for language.

If you specify DEFAULT for language, you cannot specify an alt_value.

The alt_value is limited to 30 bytes and cannot be an NLS language name, abbreviation, or DEFAULT.

Example

This example shows how to create a multi-language text table and how to set up the multi-lexer to index the table.

Create the multi-language table with a primary key, a text column, and a language column as follows:

create table globaldoc (
   doc_id number primary key,
   lang varchar2(3),
   text clob
);

Assume that the table holds mostly English documents, with the occasional German or Japanese document. To handle the three languages, you must create three sub-lexers, one for English, one for German, and one for Japanese:

ctx_ddl.create_preference('english_lexer','basic_lexer');
ctx_ddl.set_attribute('english_lexer','index_themes','yes');
ctx_ddl.set_attribtue('english_lexer','theme_language','english');

ctx_ddl.create_preference('german_lexer','basic_lexer');
ctx_ddl.set_attribute('german_lexer','composite','german');
ctx_ddl.set_attribute('german_lexer','mixed_case','yes');
ctx_ddl.set_attribute('german_lexer','alternate_spelling','german');

ctx_ddl.create_preference('japanese_lexer','japanese_vgram_lexer');

Create the multi-lexer preference:

ctx_ddl.create_preference('global_lexer', 'multi_lexer');

Since the stored documents are mostly English, make the English lexer the default:

ctx_ddl.add_sub_lexer('global_lexer','default','english_lexer');

Add the German and Japanese lexers in their respective languages. Also assume that the language column is expressed in ISO 639-2, so we add those as alternate values.

ctx_ddl.add_sub_lexer('global_lexer','german','german_lexer','ger');
ctx_ddl.add_sub_lexer('global_lexer','japanese','japanese_lexer','jpn');

Create the index globalx, specifying the multi-lexer preference and the language column in the parameters string as follows:

create index globalx on globaldoc(text) indextype is ctxsys.context
parameters ('lexer global_lexer language column lang');