Configuring a Text Attribute

As shown in Table 7-1, you can identify columns of CHAR,shorter VARCHAR2 (<=4000), BFILE, and BLOB as text attributes. If CHAR and shorter VARCHAR2 columns are not explicitly identified as unstructured text, then CREATE_MODEL processes them as categorical attributes. If BFILE and BLOB columns are not explicitly identified as unstructured text, then CREATE_MODEL returns an error.

To identify a column as a text attribute, supply the keyword TEXT in an attribute specification. The attribute specification is a field (attribute_spec) in a transformation record (transform_rec). Transformation records are components of transformation lists (xform_list) that can be passed to CREATE_MODEL.

Note:

An attribute specification can also include information that is not related to text. Instructions for constructing an attribute specification are in "Embedding Transformations in a Model" in Transforming the Data.

You can provide transformation instructions for any text attribute by qualifying the TEXT keyword in the attribute specification with the subsettings described in Table 7-7.

Table 7-7 Attribute-Specific Text Transformation Instructions

Subsetting Name Description Example

POLICY_NAME

Name of an Oracle Text policy object created with CTX_DDL.CREATE_POLICY

(POLICY_NAME:my_policy)

TOKEN_TYPE

The following values are supported:

  • NORMAL (the default)
  • STEM
  • THEME

See "Token Types in an Attribute Specification"

(TOKEN_TYPE:THEME)

MAX_FEATURES

Maximum number of features to use from the attribute.

(MAX_FEATURES:3000)

Note:

The TEXT keyword is only required for CLOB and longer VARCHAR2 (>4000) when you specify transformation instructions. The TEXT keyword is always required for CHAR, shorter VARCHAR2, BFILE, and BLOB — whether or not you specify transformation instructions.

Tip:

You can view attribute specifications in the data dictionary view ALL_MINING_MODEL_ATTRIBUTES, as shown in Oracle Database Reference.

Token Types in an Attribute Specification

When stems or themes are specified as the token type, the lexer preference for the text policy must support these types of tokens.

The following example adds themes and English stems to BASIC_LEXER.

BEGIN
  CTX_DDL.CREATE_PREFERENCE('my_lexer', 'BASIC_LEXER');
  CTX_DDL.SET_ATTRIBUTE('my_lexer', 'index_stems', 'ENGLISH');
  CTX_DDL.SET_ATTRIBUTE('my_lexer', 'index_themes', 'YES');
END;

See Also:

Example 7-1 A Sample Attribute Specification for Text

This expression specifies that text transformation for the attribute should use the text policy named my_policy. The token type is THEME, and the maximum number of features is 3000.

"TEXT(POLICY_NAME:my_policy)(TOKEN_TYPE:THEME)(MAX_FEATURES:3000)"