6 CTX_CLS Package

This chapter provides reference information for using the CTX_CLS PL/SQL package, which enables you to perform document classification.

The following procedures are described in this chapter:

Name Description
TRAIN Generates rules that define document categories. Output based on input training document set.
CLUSTERING Generates clusters for a document collection.

See Also:

The Oracle Text Application Developer's Guide for more on document classification

TRAIN

Use this procedure to generate query rules that select document categories. You must supply a training set consisting of categorized documents. Documents can be in any format supported by Oracle Text and must belong to one or more categories. This procedure generates the queries that define the categories and then writes the results to a table.

You must also have a document table and a category table. The category table must contain at least two categories.

For example, your document and category tables can be defined as:

create table trainingdoc(
docid number primary key,
text varchar2(4000));
create table category (
docid trainingdoc(docid),
categoryid number);

You can use one of two syntaxes depending on the classification algorithm you need. The query compatible syntax uses the RULE_CLASSIFIER preference and generates rules as query strings. The support vector machine syntax uses the SVM_CLASSIFER preference and generates rules in binary format. The SVM_CLASSIFIER is good for high classification accuracy, but because its rules are generated in binary format, they cannot be examined like the query strings generated with the RULE_CLASSIFIER. Note that only those document ids that appear in both the document table and the category table will impact RULE_CLASSIFIER and SVM_CLASSIFIER learning.

The CTX_CLS.TRAIN procedure requires that your document table have an associated context index. For best results, the index should be synchronized before running this procedure. SVM_CLASSIFIER syntax enables the use of an unpopulated context index, while query-compatible syntax requires that the context index be populated.

See Also:

The Oracle Text Application Developer's Guide for more on document classification

Query Compatible Syntax

The following syntax generates query-compatible rules and is used with the RULE_CLASSIFIER preference. Use this syntax and preference when different categories are separated from others by several key words. An advantage of generating your rules as query strings is that you can easily examine the generated rules. This is different from generating SVM rules, which are in binary format.

CTX_CLS.TRAIN(
index_name    in varchar2,
docid         in varchar2,
cattab        in varchar2,
catdocid      in varchar2,
catid         in varchar2,
restab        in varchar2,
rescatid      in varchar2,
resquery      in varchar2,
resconfid     in varchar2,
preference    in varchar2 DEFAULT NULL
);
index_name

Specify the name of the context index associated with your document training set.

docid

Specify the name of the document ID column in the document table. The document IDs in this column must be unique, and this column must be of datatype NUMBER. The values for this column must be stored in an unsigned 32-bit integer and must be in the range 0-4294967295.

cattab

Specify the name of the category table. You must have SELECT privilege on this table.

catdocid

Specify the name of the document ID column in the category table. The document ids in this table must also exist in the document table. This column must a NUMBER. The values for this column must be stored in an unsigned 32-bit integer and must be in the range 0-4294967295.

catid

Specify the name of the category ID column in the category table. This column must a NUMBER. The values for this column must be stored in an unsigned 32-bit integer and must be in the range 0-4294967295.

restab

Specify the name of the result table. You must have INSERT privilege on this table.

rescatid

Specify the name of the category ID column in the result table. This column must a NUMBER. The values for this column must be stored in an unsigned 32-bit integer and must be in the range 0-4294967295.

resquery

Specify the name of the query column in the result table. This column must be VARACHAR2, CHAR CLOB, NVARCHAR2, or NCHAR.

The queries generated in this column connects terms with AND or NOT operators, such as:

'T1 & T2 ~ T3'

Terms can also be theme tokens and be connected with the ABOUT operator, such as:

'about(T1) & about(T2) ~ about(T3)'

Generated rules also support WITHIN queries on field sections.

resconfid

Specify the name of the confidence column in result table. This column contains the estimated probability from training data that a document is relevant if that document satisfies the query.

preference

Specify the name of the preference. For classifier types and attributes, see Classifier Types in Chapter 2, "Oracle Text Indexing Elements".

Syntax for Support Vector Machine Rules

The following syntax generates support vector machine (SVM) rules with the SVM_CLASSIFIER preference. This preference generates rules in binary format. Use this syntax when your application requires high classification accuracy.

CTX_CLS.TRAIN(
    index_name in varchar2,    
    docid      in varchar2,         
    cattab     in varchar2, 
    catdocid   in varchar2, 
    catid      in varchar2,  
    restab     in varchar2,  
    preference in varchar2 );
index_name

Specify the name of the text index.

docid

Specify the name of docid column in document table.

cattab

Specify the name of category table.

catdocid

Specify the name of docid column in category table.

catid

Specify the name of category ID column in category table.

restab

Specify the name of result table.

The result table has the following format:

Column Name Datatype Description
CAT_ID NUMBER The ID of the category.
TYPE NUMBER(3) NOT NULL 0 for the actual rule or catid; 1 for other.
RULE BLOB The returned rule.

preference

Specify the name of user preference. For classifier types and attributes, see Classifier Types in Chapter 2, "Oracle Text Indexing Elements".

Example

The CTX_CLS.TRAIN procedure is used in supervised classification. For an extended example, see the Oracle Text Application Developer's Guide.


CLUSTERING

Use this procedure to cluster a collection of documents. A cluster is a group of documents similar to each other in content.

A clustering result set is composed of document assignments and cluster descriptions:

  • A document assignment result set shows how relevant each document is to all generated leaf clusters.

  • A cluster description result set contains information about what topic a cluster is about. This result set identifies the cluster and contains cluster description text, a suggested cluster label, and a quality score for the cluster.

Cluster output is hierarchical. Only leaf clusters are scored for relevance to documents. Producing more clusters requires more computing time. Indicate the upper limit for generated clusters with the CLUSTER_NUM attribute of the KMEAN_CLUSTERING cluster type (see "Cluster Types" in this chapter).

There are two versions of this procedure: one with a table result set, and one with an in-memory result set.

Clustering is also known as unsupervised classification.

See Also:

For more information about clustering and relevant preferences, see Cluster Types in Chapter 2, "Oracle Text Indexing Elements", as well as the Oracle Text Application Developer's Guide

Syntax: Table Result Set

ctx_cls.clustering (
 index_name  IN VARCHAR2, 
 docid       IN VARCHAR2, 
 doctab_name IN VARCHAR2, 
 clstab_name IN VARCHAR2, 
 pref_name   IN VARCHAR2  DEFAULT NULL
);
index_name

Specify the name of the context index on collection table.

docid

Specify the name of document ID column of the collection table.

doctab_name

Specify the name of document assignment table. This procedure creates the table with the following structure:

doc_assign(
   docid number,
   clusterid number,
   score number
);
Column Description
DOCID Document ID to identify document.
CLUSTERID ID of a leaf cluster associated with this document. If CLUSTERID is -1, then the cluster contains "miscellaneous" documents; for example, documents that cannot be assigned to any other cluster category.
SCORE The associated score between the document and the cluster.

If you require more columns, then create the table before you call this procedure.

clstab_name

Specify the name of the cluster description table. This procedure creates the table with the following structure:

cluster_desc(
  clusterid NUMBER,
  descript VARCHAR2(4000),
  label VARCHAR2(200),
  sze NUMBER,
  quality_score NUMBER,
  parent NUMBER
);
Column Description
CLUSTERID Cluster ID to identify cluster. If CLUSTERID is -1, then the cluster contains "miscellaneous" documents; for example, documents that cannot be assigned to any other cluster category.
DESCRIPT String to describe the cluster.
LABEL A suggested label for the cluster.
SZE This parameter currently has no value.
QUALITY_SCORE The quality score of the cluster. A higher number indicates greater coherence.
PARENT The parent cluster ID. Zero means no parent cluster.

If you require more columns, then create the table before you call this procedure.

pref_name

Specify the name of the preference.

Syntax: In-Memory Result Set

Put the result set into in-memory structures for better performance. Two in-memory tables are defined in CTX_CLS package for document assignment and cluster description respectively.

CTX_CLS.CLUSTERING(
  index_name     IN VARCHAR2, 
  docid          IN VARCHAR2,
  dids           IN DOCID_TAB,
  doctab_name    IN OUT NOCOPY DOC_TAB,
  clstab_name    IN OUT NOCOPY CLUSTER_TAB,
  pref_name      IN VARCHAR2  DEFAULT NULL 
          );
index_name

Specify the name of context index on the collection table.

docid

Specify the document ID column of the collection table.

dids

Specify the name of the in-memory docid_tab.

TYPE docid_tab IS TABLE OF number INDEX BY BINARY_INTEGER;
doctab_name

Specify name of the document assignment in-memory table. This table is defined as follows:

TYPE doc_rec IS RECORD (
   docid NUMBER,
   clusterid NUMBER,
   score NUMBER
)
TYPE doc_tab IS TABLE OF doc_rec INDEX BY BINARY_INTEGER;
Column Description
DOCID Document ID to identify document.
CLUSTERID ID of a leaf cluster associated with this document. If CLUSTERID is -1, then the cluster contains "miscellaneous" documents; for example, documents that cannot be assigned to any other cluster category.
SCORE The associated score between the document and the cluster.

cls_tab

Specify the name of cluster description in-memory table.

TYPE cluster_rec IS RECORD(
     clusterid NUMBER,
     descript VARCHAR2(4000),
     label VARCHAR2(200),
     sze NUMBER,
     quality_score NUMBER,
     parent NUMBER
);
TYPE cluster_tab IS TABLE OF cluster_rec INDEX BY BINARY_INTEGER;
Column Description
CLUSTERID Cluster ID to identify cluster. If CLUSTERID is -1, then the cluster contains "miscellaneous" documents; for example, documents that cannot be assigned to any other cluster category.
DESCRIPT String to describe the cluster.
LABEL A suggested label for the cluster.
SZE This parameter currently has no value.
QUALITY_SCORE The quality score of the cluster. A higher number indicates greater coherence.
PARENT The parent cluster ID. Zero means no parent cluster.

pref_name

Specify the name of the preference. For cluster types and attributes, see Cluster Types in Chapter 2, "Oracle Text Indexing Elements".

Example

See Also:

The Oracle Text Application Developer's Guide for an example of using clustering