How to get the narrower terms of a category in the supplied knowledgebase?

Question

I want to add more medical terms for cardiovascular disorders to the supplied knowledge base of Oracle Text for better theme extraction. (Oracle 10g release 2, Oracle Text version 10.2.0.1.0 )
Based on the "English Knowledge Base Category Hierarchy" documented at http://www.oracle.com/technology/products/text/index.html , I think I want to add more diseases names to "science and technology->life sciences->health and medicine->medical problems->cardiovascular disorders".
Before doing that, I hope I can see the existing narrower terms under "cardiovascular disorders". I tried ctx_query.hfeedback() following the example in Oracle Text reference.
But, I got the following error messages where I tried to print out content in the result table at the end:
SQL> CREATE TABLE text (
2 id NUMBER primary key,
3 text VARCHAR2(4000)
4 );
Table created.
SQL> insert into text values (1,'This is about cardiovascular disorders. Cardiovascular disorders terms will be extended');
1 row created.
SQL> exec ctx_ddl.set_attribute('mylex','index_themes','YES');
PL/SQL procedure successfully completed.
SQL> exec ctx_ddl.set_attribute('mylex','index_text','YES');
PL/SQL procedure successfully completed.
SQL> create index idx_text on text(text)
2 indextype is ctxsys.context
3 parameters('lexer mylex');
Index created.
SQL> set serveroutput on
SQL> declare
2 the_themes ctx_doc.theme_tab;
3 begin
4 ctx_doc.themes('idx_text','1',the_themes);
5 for i in 1..the_themes.count loop
6 dbms_output.put_line(the_themes(i).theme||':'||the_themes(i).weight);
7 end loop;
8 end;
9 /
cardiovascular disorders:87
extensions:51
PL/SQL procedure successfully completed.
SQL> CREATE TABLE restab (
2 feedback_id VARCHAR2(30),
3 id NUMBER,
4 parent_id NUMBER,
5 operation VARCHAR2(30),
6 options VARCHAR2(30),
7 object_name VARCHAR2(80),
8 position NUMBER,
9 bt_feedback ctxsys.ctx_feedback_type,
10 rt_feedback ctxsys.ctx_feedback_type,
11 nt_feedback ctxsys.ctx_feedback_type
12 ) NESTED TABLE bt_feedback STORE AS res_bt
13 NESTED TABLE rt_feedback STORE AS res_rt
14 NESTED TABLE nt_feedback STORE AS res_nt;
Table created.
SQL> BEGIN
2 ctx_query.hfeedback (index_name => 'idx_text',
3 text_query => 'blood disorders',
4 feedback_table => 'restab',
5 sharelevel => 0,
6 feedback_id => 'query1'
7 );
8 END;
9 /
PL/SQL procedure successfully completed.
SQL> DECLARE
2 i NUMBER;
3 BEGIN
4 FOR frec IN (
5 SELECT object_name, nt_feedback
6 FROM restab
7 WHERE feedback_id = 'query1' AND object_name IS NOT NULL
8 ) LOOP
9
10 dbms_output.put_line('Narrower term feedback for ' || frec.object_name
||
11 ':');
12 i := frec.nt_feedback.FIRST;
13 WHILE i IS NOT NULL LOOP
14 dbms_output.put_line(frec.nt_feedback(i).text);
15 i := frec.nt_feedback.NEXT(i);
16 END LOOP;
17
18 END LOOP;
19 END;
20 /
DECLARE
ERROR at line 1:
ORA-06531: Reference to uninitialized collection
ORA-06512: at line 12
any thought?
Thanks in advance,
-Haijun

Answer 1

You can avoid the error by wrapping an if .. end if around the problem section, like so:
IF frec.nt_feedback IS NOT NULL THEN
i := frec.nt_feedback.FIRST;
WHILE i IS NOT NULL LOOP
dbms_output.put_line(frec.nt_feedback(i).text);
i := frec.nt_feedback.NEXT(i);
END LOOP;
END IF;
However, the reason that you are getting the error is because the nt_feedback is empty. You can see this by simply:
select * from restab;
The reason is that ctx_query.hfeedback is intended for finding narrower terms within your index that match narrower terms within your knowledge base. Since there is only one row in your table, there are no narrow terms to be found.
To find narrower terms in your knowledge base, all you need is:
SELECT CTX_THES.NT ('your_broad_term_goes_here') FROM DUAL;
You may need to run the query as CTXSYS and specify the thesaurus name, if it is not part of the default thesaurus. You can also specify the level of narrower terms. A medthes must be purchased and loaded separately. I don't have a complete medthes, so the following is just a brief example, having loaded just a few terms:
CTXSYS@orcl_11g> SELECT CTX_THES.NT ('health and medicine', 10, 'MEDTHES') from dual;
CTX_THES.NT('HEALTHANDMEDICINE',10,'MEDTHES')
{health and medicine}|{Anesthesia and Analgesia}|{Anti-Allergic and Respiratory
System Agents}|{Anti-Inflamammatory Agents, Antirheumatic Agents, and Inflamatio
n Mediators}|{Antineoplastic and Immunosuppressive Agents}
CTXSYS@orcl_11g>