HIGHLIGHT

Use the CTX_DOC.HIGHLIGHT procedure to generate highlight offsets for a document. The offset information is generated for the terms in the document that satisfy the query you specify. These highlighted terms are either the words that satisfy a word query or the themes that satisfy an ABOUT query.

You can generate highlight offsets for either plaintext or HTML versions of the document. Yo can apply the offset information to the same documents filtered with CTX_DOC.FILTER.

You usually call this procedure after a query, from which you identify the document to be processed.

You can store the highlight offsets in either an in-memory PL/SQL table or a result table.

Syntax 1:In-Memory Result Storage

CTX_DOC.HIGHLIGHT(
        index_name  IN VARCHAR2, 
        textkey     IN VARCHAR2, 
        text_query  IN VARCHAR2, 
        restab      IN OUT NOCOPY HIGHLIGHT_TAB, 
        plaintext   IN BOOLEAN  DEFAULT FALSE);

Syntax 2:Result Table Storage

CTX_DOC.HIGHLIGHT(
          index_name  IN VARCHAR2, 
          textkey     IN VARCHAR2, 
          text_query  IN VARCHAR2, 
          restab      IN VARCHAR2, 
          query_id    IN NUMBER   DEFAULT 0,
          plaintext   IN BOOLEAN  DEFAULT FALSE);

index_name

Specify the name of the index associated with the text column containing the document identified by textkey.

textkey

Specify the unique identifier (usually the primary key) for the document.

The textkey parameter can be one of the following:

• a single column primary key value

• encoded specification for a composite (multiple column) primary key. Use the CTX_DOC.PKENCODE procedure.

• the rowid of the row containing the document

You toggle between primary key and rowid identification using CTX_DOC.SET_KEY_TYPE.

text_query

Specify the original query expression used to retrieve the document. If NULL, no highlights are generated.

If text_query includes wildcards, stemming, fuzzy matching which result in stopwords being returned, HIGHLIGHT does not highlight the stopwords.

If text_query contains the threshold operator, the operator is ignored. The HIGHLIGHT procedure always returns highlight information for the entire result set.

restab

You can specify that this procedure store highlight offsets to either a table or to an in-memory PL/SQL table.

To store results to a table specify the name of the table. The table must exist before you call this procedure.

See Also: see "Highlight Table" in Appendix A for more information about the structure of the highlight result table.

To store results to an in-memory table, specify the name of the in-memory table of type CTX_DOC.HIGHLIGHT_TAB. The HIGHLIGHT_TAB datatype is defined as follows:

type highlight_rec is record (
  offset number;
  length number;
);
type highlight_tab is table of highlight_rec index by binary_integer;

CTX_DOC.HIGHLIGHT clears HIGHLIGHT_TAB before the operation.

query_id

Specify the identifier used to identify the row inserted into restab.

When query_id is not specified or set to NULL, it defaults to 0. You must manually truncate the table specified in restab.

plaintext

Specify TRUE to generate a plaintext offsets of the document.

Specify FALSE to generate HTML offsets of the document if you are using the INSO filter or indexing HTML documents.

Examples

Create Highlight Table

Create the highlight table to store the highlight offset information:

create table hightab(query_id number, 
                     offset number, 
                     length number);

Word Highlight Offsets

To obtain HTML highlight offset information for document 20 for the word dog:

begin
ctx_doc.highlight('newsindex', '20', 'dog', 'hightab', 0, FALSE);
end;

Theme Highlight Offsets

Assuming the index newsindex has a theme component, you obtain HTML highlight offset information for the theme query of politics by issuing the following query:

begin
ctx_doc.highlight('newsindex', '20', 'about(politics)', 'hightab', 0, FALSE);
end;

The output for this statement are the offsets to highlighted words and phrases that represent the theme of politics in the document.