A chunked output, especially for long and complex documents, sometimes loses contextual meaning or coherence with its parent content. In this example, you can see how to refine your chunks by applying custom chunking specifications.

1. Connect to Oracle Database as a local user.
   1. Log in to SQL*Plus as the SYS user, connecting as SYSDBA:

      conn sys/password as sysdba

      CREATE TABLESPACE tbs1
      DATAFILE 'tbs5.dbf' SIZE 20G AUTOEXTEND ON
      EXTENT MANAGEMENT LOCAL
      SEGMENT SPACE MANAGEMENT AUTO;

      SET ECHO ON
      SET FEEDBACK 1
      SET NUMWIDTH 10
      SET LINESIZE 80
      SET TRIMSPOOL ON
      SET TAB OFF
      SET PAGESIZE 10000
      SET LONG 10000

   2. Create a local test user (docuser) and grant necessary privileges:

      DROP USER docuser cascade;

      CREATE USER docuser identified by docuser DEFAULT TABLESPACE tbs1 quota unlimited on tbs1;

      GRANT DB_DEVELOPER_ROLE to docuser;

   3. Connect as the local user (docuser):

      CONN docuser/password

2. Create a relational table (documentation_tab) to store unstructured text chunks in it:

   DROP TABLE IF EXISTS documentation_tab; 
   
   CREATE TABLE documentation_tab (
       id NUMBER, 
       text VARCHAR2(2000));

   INSERT INTO documentation_tab VALUES(1,
   'Oracle AI Vector Search stores and indexes vector embeddings'||
   ' for fast retrieval and similarity search.'||CHR(10)||CHR(10)||
   '    About Oracle AI Vector Search'||CHR(10)||
   '    Vector Indexes are a new classification of specialized indexes'||
   ' that are designed for Artificial Intelligence (AI) workloads that allow'||
   ' you to query data based on semantics, rather than keywords.'||CHR(10)||CHR(10)||
   '    Why Use Oracle AI Vector Search?'||CHR(10)||
   ' The biggest benefit of Oracle AI Vector Search is that semantic search'||
   ' on unstructured data can be combined with relational search on business'||
   ' data in one single system.'||CHR(10));
   
   COMMIT;

   SET LINESIZE 1000;
   SET PAGESIZE 200;
   COLUMN doc FORMAT 999;
   COLUMN id  FORMAT 999;
   COLUMN pos FORMAT 999;
   COLUMN siz FORMAT 999;
   COLUMN txt FORMAT a60;
   COLUMN data FORMAT a80;

3. Call the VECTOR_CHUNKS SQL function and specify the following custom chunking parameters. Setting the NORMALIZE parameter to all ensures that the formatting of the results is easier to read, which is especially helpful when the data includes PDF documents:

   SELECT D.id doc, C.chunk_offset pos, C.chunk_length siz, C.chunk_text txt
   FROM documentation_tab D, VECTOR_CHUNKS(D.text 
       BY words
       MAX 50
       OVERLAP 0
       SPLIT BY recursively
       LANGUAGE american
       NORMALIZE all) C;

   To call the same operation using the UTL_TO_CHUNKS function from the DBMS_VECTOR_CHAIN package, run:

   SELECT D.id doc,
       JSON_VALUE(C.column_value, '$.chunk_id' RETURNING NUMBER) AS id,
       JSON_VALUE(C.column_value, '$.chunk_offset' RETURNING NUMBER) AS pos,
       JSON_VALUE(C.column_value, '$.chunk_length' RETURNING NUMBER) AS siz,
       JSON_VALUE(C.column_value, '$.chunk_data') AS txt
   FROM documentation_tab D,
      dbms_vector_chain.utl_to_chunks(D.text,
      JSON('{"by":"words",
             "max":"50",
             "overlap":"0",
             "split":"recursively",
             "language":"american",
             "normalize":"all"}')) C;

   This returns a set of three chunks, which are split by words recursively using blank lines, new lines, and spaces:

   DOC  POS  SIZ  TXT
   ---- ---- ---- ------------------------------------------------------------
   1   1    108   Oracle AI Vector Search stores and indexes vector embeddings
   		 for fast retrieval and similarity search.
   
   1   109  234   About Oracle AI Vector Search
   	        Vector Indexes are a new classification of specialized index
   	        es that are designed for Artificial Intelligence (AI) worklo
   	        ads that allow you to query data based on semantics, rather
   	        than keywords.
   
   1   343  204   Why Use Oracle AI Vector Search?
   	        The biggest benefit of Oracle AI Vector Search is that seman
   	        tic search on unstructured data can be combined with relatio
   	        nal search on business data in one single system.

   The chunking results contain:

   • chunk_id as DOC: ID for each chunk

   • chunk_offset as POS: Original position of each chunk in the source document, relative to the start of document (which has a position of 1)

   • chunk_length as SIZ: Character length of each chunk

   • chunk_data as TXT: Textual content from each chunk