14 Oracle Text Utilities

14.1.1 Text Loading

The ctxload program no longer supports the loading of text columns. To load files to a text column in batch mode, Oracle recommends that you use SQL*Loader.

14.1.2 ctxload Syntax

ctxload -user username[/password][@sqlnet_address]
        -name object_name 
        -file file_name 
      
       [-thes]
       [-thescase y|n]
       [-thesdump]
       [-log file_name]
       [-trace]
       [-drop]

14.1.3 ctxload Examples

This section provides examples for some of the operations that ctxload can perform.

ctxload -user jsmith/123abc -thes -name tech_doc -file tech_thesaurus.txt 

ctxload -user jsmith/123abc -thesdump -name tech_doc -file tech_thesaurus.out 

14.2.1 Knowledge Base Character Set

Knowledge bases can be in any single-byte character set. Supplied knowledge bases are in WE8ISO8859P1. You can store an extended knowledge base in another character set such as US7ASCII.

14.2.2 ctxkbtc Syntax

ctxkbtc -user uname/passwd

[-name thesname1 [thesname2 ... thesname16]]
[-revert]
[-stoplist stoplistname]
[-verbose]
[-log filename]

-user

Specify the user name and password for the administrator creating an extended knowledge base. This user must have write permission to the ORACLE_HOME directory.

-name thesname1 [thesname2 ... thesname16]

Specify the names of the thesauri (up to 16) to be compiled with the knowledge base to create the extended knowledge base. The thesauri you specify must already be loaded with ctxload with the "-thescase Y" option

-revert

Reverts the extended knowledge base to the default knowledge base provided by Oracle Text.

-stoplist stoplistname

Specify the name of the stoplist. Stopwords in the stoplist are added to the knowledge base as useless words that are prevented from becoming themes or contributing to themes. Add stopthemes after running this command using CTX_DLL.ADD_STOPTHEME.

-verbose

Displays all warnings and messages, including non-Globalization Support messages, to the standard output.

-log

Specify the log file for storing all messages. When you specify a log file, no messages are reported to standard out.

14.2.3 ctxkbtc Usage Notes

• Before running ctxkbtc, you must set the NLS_LANG environment variable to match the database character set.

• The user issuing ctxkbtc must have write permission to the ORACLE_HOME, because the program writes files to this directory.

• Before being compiled, each thesaurus must be loaded into Oracle Text case sensitive with the "-thescase Y" option in ctxload.

• Running ctxkbtc twice removes the previous extension.

14.2.4 ctxkbtc Limitations

The ctxkbtc program has the following limitations:

• When upgrading or downgrading your database to a different release, for theme indexing and related features to work correctly, Oracle recommends that you recompile your extended knowledge base in the new environment.

• Before extending the knowledge base, you must terminate all server processes that have invoked any knowledge base-related Text functions during their lifetime.

• There can be only one user extension for each language for each installation. Because a user extension affects all users at the installation, only the CTXSYS user can extend the knowledge base.

• In an Oracle RAC environment, the ORACLE_HOME can either be shared between multiple nodes, or each node can have its own ORACLE_HOME. The following requirements apply:

  • Before using any knowledge base-dependent functionality in any of the Oracle RAC nodes, ctxkbtc must be run in every ORACLE_HOME in the Oracle RAC environment.

  • When using ctxkbtc, the exact same input thesaurus content must be used in every ORACLE_HOME in the Oracle RAC environment.

14.2.5 ctxkbtc Constraints on Thesaurus Terms

Terms are case sensitive. If a thesaurus has a term in uppercase, for example, the same term present in lowercase form in a document will not be recognized.

The maximum length of a term is 80 characters.

Disambiguated homographs are not supported.

14.2.6 ctxkbtc Constraints on Thesaurus Relations

The following constraints apply to thesaurus relations:

• BTG and BTP are the same as BT. NTG and NTP are the same as NT.

• Only preferred terms can have a BT, NTs or RTs.

• If a term has no USE relation, it will be treated as its own preferred term.

• If a set of terms are related by SYN relations, only one of them may be a preferred term.

• An existing category cannot be made a top term.

• There can be no cycles in BT and NT relations.

• A term can have at most one preferred term and at most one BT. A term may have any number of NTs.

• An RT of a term cannot be an ancestor or descendent of the term. A preferred term may have any number of RTs up to a maximum of 32.

• The maximum height of a tree is 16 including the top term level.

• When multiple thesauri are being compiled, a top term in one thesaurus should not have a broader term in another thesaurus.

  Note:

  The thesaurus compiler tolerates some violations of the preceding rules. For example, if a term has multiple BTs, then the compiler ignores all but the last one it encounters.

  Similarly, BTs between existing knowledge base categories result only in a warning message.

  Oracle recommends that you do not set up extended storage bases with violations. Using extended storage bases containing violations can produce undesired results.

14.2.7 Extending the Knowledge Base

Extend the supplied knowledge base by compiling one or more thesauri with the Oracle Text knowledge base. The extended information can be application-specific terms and relationships. During theme analysis, the extended portion of the knowledge base overrides any terms and relationships in the knowledge base where there is overlap.

When extending the knowledge base, Oracle recommends that new terms be linked to one of the categories in the knowledge base for best results in theme proving when appropriate.

If new terms are kept completely disjoint from existing categories, fewer themes from new terms will be proven. The result of this is poorer precision and recall with ABOUT queries as well poor quality of gists and theme highlighting.

Link new terms to existing terms by making an existing term the broader term for the new terms.

health and medicine
 NT Anesthesia and Analgesia
 NT Anti-Allergic and Respiratory System Agents
 NT Anti-Inflamammatory Agents, Antirheumatic Agents, and Inflamation Mediators
 NT Antineoplastic and Immunosuppressive Agents

setenv NLS_LANG AMERICAN_AMERICA.WE8ISO8859P1

ctxload -thes -thescase y -name medthes -file med.thes -user ctxsys/ctxsys

ctxkbtc -user ctxsys/ctxsys -name medthes 

14.2.8 Adding a Language-Specific Knowledge Base

Extend theme functionality to languages other than English or French by loading your own knowledge base for any single-byte whitespace delimited language, including Spanish.

Theme functionality includes theme indexing, ABOUT queries, theme highlighting, and the generation of themes, gists, and theme summaries with the CTX_DOC PL/SQL package.

Extend theme functionality by adding a user-defined knowledge base. For example, you can create a Spanish knowledge base from a Spanish thesaurus.

To load your language-specific knowledge base, follow these steps:

1. Load your custom thesaurus using ctxload.

2. Set NLS_LANG so that the language portion is the target language. The charset portion must be a single-byte character set.

3. Compile the loaded thesaurus using ctxkbtc:

ctxkbtc -user ctxsys/ctxsys -name my_lang_thes

This command compiles your language-specific knowledge base from the loaded thesaurus. To use this knowledge base for theme analysis during indexing and ABOUT queries, specify the NLS_LANG language as the THEME_LANGUAGE attribute value for the BASIC_LEXER preference.

14.2.9 Order of Precedence for Multiple Thesauri

When multiple thesauri are to be compiled, precedence is determined by the order in which thesauri are listed in the arguments to the compiler, assumed to be most preferred first. A user-defined thesaurus always has precedence over the built-in knowledge base.

14.2.10 Size Limits for Extended Knowledge Base

The following table lists the size limits associated with creating and compiling an extended knowledge base.

14.3.1 Syntax of ctxlc

ctxlc has the following syntax:

ctxlc -ja | -zh [ -n ] -ics character_set -i input_file

ctxlc -ja | -zh -ocs character_set [ > output_file ]

14.3.2 Performance Considerations

You can add up to 1,000,000 new words to a lexicon. However, creating a very large lexicon can reduce performance in indexing and querying. Performance is best when the lexicon character set is UTF-8. There is no performance impact on the Chinese or Japanese V-gram lexers, as they do not use lexicons.

14.3.3 ctxlc Usage Notes

Oracle recommends the following practices with regard to ctxlc:

• Save your plain text dictionary file in your environment for emergency use.

• When upgrading or downgrading your database to a different release, recompile your plain text dictionary file in the new environment so that the user lexicon will work correctly.

14.3.4 Example

In this example, you create a new Japanese lexicon from the file jadict.txt, a word list that uses the JA16EUC character set. Because you are not specifying -n, the new lexicon is the result of merging jadict.txt with the system Japanese lexicon. Then replace the existing Japanese lexicon with the new, merged one.

% ctxlc -ja -ics JA16EUC -i jadict.txt

This creates new files in the current directory:

% ls
drold.dat
drolk.dat
droli.dat
drolt.dat

The system lexicon files for Japanese and Chinese are named droldxx.dat drolkxx.dat, and drolixx.dat, where xx is either JA (for Japanese) or ZH (for Chinese). Rename the three new files and copy them to the directory containing the system Japanese lexicon.

% mv drold.dat droldJA.dat
% mv drolk.dat drolkJA.dat
% mv droli.dat droliJA.dat
% cp *dat $ORACLE_HOME/ctx/data/jalx

This replaces the system Japanese lexicon with one that is a merge of the old system lexicon and your wordlist from jadict.txt.

You can also use ctxlc to get a dump of a system lexicon. This example dumps the Chinese lexicon to a file called new_chinese_dict.txt in the current directory:

% ctxlc -zh -ocs UTF8 > new_chinese_dict.txt

This creates a file, new_japanese.dict.txt, using the UTF8 character set, in the current directory.