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Managing ConText Indexes: DBMS_XDBT in PL/SQL

The DBMS_XDBT Package enables an administrator to create a ConText index on the XML DB hierarchy and configure it for automatic maintenance.

This chapter contains the following sections:

• Description of DBMS_XDBT
• Procedures and Functions of DBMS_XDBT
• Customizing the DBMS_XDBT package

  See Also: Oracle9i XML Database Developer's Guide - Oracle XML DB Oracle9i Supplied PL/SQL Packages and Types Reference

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DBMS_XDBT Package

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Description of DBMS_XDBT

The DBMS_XDBT package provides a convenient mechanism for administrators to set up a ConText index on the Oracle XML DB Hierarchy. The package contains procedures to create default preferences, create the index and set up automatic synchronization of the context index

The DBMS_XDBT package also contains a set of package variables that describe the configuration settings for the index. These are intended to cover the basic customizations that installations may require, but is by no means a complete set.

The DBMS_XDBT package can be used in the following fashion:

• Customize the package to set up the appropriate configuration.
• Drop any existing index preferences using the dropPreferences() procedure.
• Create new index preferences using the createPreferences() procedure.
• Create the ConText index using the createIndex() procedure.
• Set up automatic synchronization of the index using the configureAutoSync() procedure.

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Procedures and Functions of DBMS_XDBT

Table 33-1 Summary of Procedures and Functions of DBMS_XDBT  

Procedure/Function	Description
dropPreferences()	Drops any existing preferences.
createPreferences()	Creates preferences required for the ConText index on the XML DB hierarchy.
createDatastorePref()	Creates a USER datastore preference for the ConText index.
createFilterPref()	Creates a filter preference for the ConText index.
createLexerPref()	Creates a lexer preference for the ConText index.
createWordlistPref()	Creates a stoplist for the ConText index.
createStoplistPref()	Creates a section group for the ConText index.
createStoragePref()	Creates a wordlist preference for the ConText index.
createSectiongroupPref()	Creates a storage preference for the ConText index.
createIndex()	Creates the ConText index on the XML DB hierarchy.
configureAutoSync()	Configures the ConText index for automatic maintenance (SYNC).

dropPreferences()

Description

This procedure drops any previously created preferences for the ConText index on the XML DB hierarchy.

Syntax

PROCEDURE dropPreferences;

createPreferences()

Description

This procedure creates a set of default preferences based on the configuration settings.

Syntax

PROCEDURE createPreferences;

createDatastorePref()

Description

This procedure creates a USER datastore preference for the ConText index on the XML DB hierarchy.

• The name of the datastore preference can be modified; see the DatastorePref configuration setting.
• The default USER datastore procedure also filters the incoming document. The DBMS_XDBT package provides a set of configuration settings that control the filtering process.
• The SkipFilter_Types array contains a list of regular expressions. Documents with a mime type that matches one of these expressions are not indexed. Some of the properties of the document metadata, such as author, remain unindexed.
  • The NullFilter_Types array contains a list of regular expressions. Documents with a mime type that matches one of these expressions are not filtered; however, they are still indexed. This is intended to be used for documents that are text-based, such as HTML, XML and plain-text.
  • All other documents use the INSO filter through the IFILTER API.

Syntax

PROCEDURE createDatastorePref;

createFilterPref()

Description

This procedure creates a NULL filter preference for the ConText index on the XML DB hierarchy.

• The name of the filter preference can be modified; see FilterPref configuration setting.
• The USER datastore procedure filters the incoming document; see createDatastorePref for more details.

Syntax

PROCEDURE createFilterPref;

createLexerPref()

Description

This procedure creates a BASIC lexer preference for the ConText index on the XML DB hierarchy.

• The name of the lexer preference can be modified; see LexerPref configuration setting. No other configuration settings are provided.
• MultiLexer preferences are not supported.
• Base letter translation is turned on by default.

Syntax

PROCEDURE createLexerPref;

createWordlistPref()

Description

This procedure creates a wordlist preference for the ConText index on the XML DB hierarchy.

• The name of the wordlist preference can be modified; see the WordlistPref configuration setting. No other configuration settings are provided.
• FUZZY_MATCH and STEMMER attributes are set to AUTO (auto-language detection)

Syntax

PROCEDURE createWordlistPref;

createStoplistPref()

Description

This procedure creates a stoplist for the ConText index on the XML DB hierarchy.

• The name of the stoplist can be modified; see the StoplistPref configuration setting.
• Numbers are not indexed.
• The StopWords array is a configurable list of stopwords. These are meant to be stopwords in addition to the set of stopwords in CTXSYS.DEFAULT_STOPLIST.

Syntax

PROCEDURE createStoplistPref;

createStoragePref()

Description

This procedure creates a BASIC_STORAGE preference for the ConText index on the XML DB hierarchy.

• The name of the storage preference can be modified; see the StoragePref configuration setting.
• A tablespace can be specified for the tables and indexes comprising the ConText index; see the IndexTablespace configuration setting.
• Prefix and Substring indexing are not turned on by default.
• The I_INDEX_CLAUSE uses key compression.

Syntax

PROCEDURE createStoragePref;

createSectiongroupPref()

Description

This procedure creates a section group for the ConText index on the XML DB hierarchy.

• The name of the section group can be changed; see the SectiongroupPref configuration setting.
• The HTML sectioner is used by default. No zone sections are created by default. If the vast majority of documents are XML, consider using the AUTO_SECTION_GROUP or the PATH_SECTION_GROUP; see the SectionGroup configuration setting.

Syntax

PROCEDURE createSectiongroupPref;

createIndex()

Description

This procedure creates the ConText index on the XML DB hierarchy.

Syntax

PROCEDURE createIndex;

Notes

• The name of the index can be changed; see the IndexName configuration setting.
• Set the LogFile configuration parameter to enable ROWID logging during index creation.
• Set the IndexMemory configuration parameter to determine the amount of memory that index creation, and later SYNCs, will use.

configureAutoSync()

Description

This procedure sets up jobs for automatic SYNCs of the ConText index.

• The system must be configured for job queues for automatic synchronization. The jobs can be viewed using the USER_JOBS catalog views
• The configuration parameter AutoSyncPolicy can be set to choose an appropriate synchronization policy.

The synchronization can be based on one of the following:

SYNC_BY_PENDING_COUNT	The SYNC is triggered when the number of documents in the pending queue is greater than a threshold (See the MaxPendingCount configuration setting) The pending queue is polled at regular intervals (See the CheckPendingCountInterval configuration parameter) to determine if the number of documents exceeds the threshold
SYNC_BY_TIME	The SYNC is triggered at regular intervals. See the SyncInterval configuration parameter.
SYNC_BY_PENDING_COUNT_AND_TIME	A combination of both SYNC_BY_PENDING_COUNT and SYNC_BY_TIME

Syntax

PROCEDURE configureAutoSync;

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Customizing the DBMS_XDBT package

The DBMS_XDBT package can be customized in one of two ways.

• Using a PL/SQL procedure, or an anonymous block, to set the relevant package variables (configuration settings), and then executing the procedures in this package.
• The more general approach is to introduce the appropriate customizations by modifying this package in place, or as a copy.

Please note that the system must be configured to use job queues, and that the jobs can be viewed through the USER_JOBS catalog views.

This section describes the configuration settings, or package variables, available to customize the DBMS_XDBT package.

General Indexing Settings

The following table lists configuration settings that are relevant to general indexing.

Parameter	Default Values	Description
IndexName	XDB$CI	The name of the ConText index.
IndexTablespace	XDB$RESINFO	The tablespace used by tables and indexes comprising the ConText index.
IndexMemory	128M	Memory used by index creation and Sync. This must be less than (or equal to) the MAX_INDEX_MEMORY system parameter. The MAX_INDEX_MEMORY system parameter (see the CTX_ADMIN package) must be greater than or equal to the IndexMemory setting.
LogFile	'XdbCtxLog'	The logfile used for ROWID logging during index creation. The LOG_DIRECTORY system parameter must be set already. Set this to NULL to turn off ROWID logging. The LOG_DIRECTORY system parameter (see the CTX_ADMIN package) must be set to enable ROWID logging.

Filtering Settings

The following table lists configuration settings that control the filtering of documents in the XML DB hierarchy.

Parameter	Default Value(s)	Description
SkipFilter_Types	image/%, audio/%, video/%, model/%	List of mime types that should not be indexed.
NullFilter_Types	text/plain, text/html, text/xml	List of mime types that do not need to use the INSO filter. Use this for text-based documents.
FilterPref	XDB$CI_FILTER	Name of the filter preference.

Sectioning and Section Group Settings

The following table lists configuration settings relevant to the sectioner.

Parameter	Default Value	Description
SectionGroup	HTML_SECTION_GROUP	Default sectioner to use. Consider using PATH_SECTION_GROUP or AUTO_SECTION_GROUP if the repository contains mainly XML documents.
SectiongroupPref	XDB$CI_SECTIONGROUP	Name of the section group.

Stoplist Settings

The following table lists stoplist configuration settings.

Parameter	Default Value(s)	Description
StoplistPref	XDB$CI_STOPLIST	Name of the stoplist.
StopWords	0..9 'a'..'z' 'A'..'Z'	List of stopwords, in addition to stopwords specified in CTXSYS.DEFAULT_STOPLIST.

Other Preference Settings

The following table lists settings for other index preferences.

Parameter	Default Value	Description
DatastorePref	XDB$CI_DATASTORE	The name of the datastore preference.
StoragePref	XDB$CI_STORAGE	The name of the storage preference.
WordlistPref	XDB$CI_WORDLIST	The name of the wordlist preference.
DefaultLexerPref	XDB$CI_DEFAULT_LEXER	The name of the default lexer preference.

Index SYNC settings

The following table lists settings that control when and how the ConText index is synchronized.

Parameter	Default Value(s)	Description
AutoSyncPolicy	SYNC_BY_PENDING_COUNT	Indicates when the index should be SYNCed. Can be one of: - SYNC_BY_PENDING_COUNT, - SYNC_BY_TIME, or - SYNC_BY_PENDING_COUNT_AND_TIME.
MaxPendingCount	2	Maximum number of documents in the CTX_USER_PENDING queue for this index before an index SYNC is triggered. Applies only if the AutoSyncPolicy is one of: - SYNC_BY_PENDING_COUNT, or - SYNC_BY_PENDING_COUNT_AND_TIME.
CheckPendingCountInterval	10 minutes	Indicates how often, in minutes, the pending queue should be checked. Applies only if the AutoSyncPolicy is one of: - SYNC_BY_PENDING_COUNT, or - SYNC_BY_PENDING_COUNT_AND_TIME.
SyncInterval	60 minutes	Indicates how often, in minutes, the index should be SYNCed. Applies only if the AutoSyncPolicy is one of: - SYNC_BY_TIME, or - SYNC_BY_PENDING_COUNT_AND_TIME