Indexing

Once your text data is loaded in a table and the table contains a primary key, you can run the command to create a Text index.

For example, the following command creates a Text index called myindex on the text column in the docs table:

create index myindex on docs(text) indextype is ctxsys.context;

General Defaults for All Languages

When you use CREATE INDEX without explicitly specifying parameters, the system does the following for all languages by default:

• Assumes that the text to be indexed is stored directly in a text column. The text column can be of type CLOB, BLOB, BFILE, VARCHAR2, or CHAR. The columns types LONG and LONG RAW are supported for migrating Oracle7 systems to Oracle8i. The column types NCLOB, DATE and NUMBER cannot be indexed

• Detects the column type and uses filtering for binary column types. Most document formats are supported for filtering. If your column is plain text, the system does not use filtering.

  Note: For document filtering to work correctly in your system, you must ensure that your environment is set up correctly to support the Inso filter. To learn more about configuring your environment to use the Inso filter, see "About Inso Filtering Technology" in Appendix C.

• Assumes the language of text to index is the language you specify in your database setup.

• Uses the default stoplist for the language you specify in your database setup. Stoplists identify the words that the system ignores during indexing.

• Enables fuzzy and stemming queries for your language, if this feature is available for your language.

You can always change the default indexing behavior by creating your own preferences and specifying these custom preferences in the parameter string of CREATE INDEX.

See Also: To learn more about creating your own custom preferences, see Chapter 3, "Indexing". See also CTX_DDL.CREATE_PREFERENCE in Chapter 7. To learn more about using CREATE INDEX, see its specification in Chapter 2.

Language Specific Defaults

American and English Language Defaults

In addition to the general defaults, the system enables the following option for American and English language text:

• Indexes document theme information. When theme information is indexed, ABOUT queries are more precise

Danish Language Defaults

In addition to the general defaults, the system enables the following options for Danish text:

• Alternate spelling

Dutch Language Defaults

In addition to the general defaults, the system enables the following options for Dutch text:

• Composite indexing

• Alternate spelling

Finnish, Norwegian, and Swedish Language Defaults

In addition to the general defaults, the system enables the following option for Finnish, Norwegian, and Swedish text:

• Alternate spelling

German and German DIN Language Defaults

In addition to the general defaults, the system enables the following options for German text:

• Case-sensitive indexing

• Composite indexing

• Alternate spelling

  .

  See Also: To learn more about these options, see BASIC_LEXER in Chapter 3.

Index Maintenance

Index maintenance is necessary after your application inserts, updates, or deletes documents in your base table.

If your base table is static, that is, you do no updating, inserting or deleting of documents after your initial index, you do not need to maintain your index.

However, if you perform DML (inserts, updates, or deletes) on your base table, you must update your index. You can synchronize your index manually with ALTER INDEX. You can also run the ctxsrv server in the background which synchronizes the index automatically at regular intervals.

See Also: For more information about synchronizing the index, see ALTER INDEX in Chapter 2. For more information about ctxsrv, see "ctxsrv" in Chapter 11.