Oracle8 ConText Cartridge Workbench User's Guide
Release 2.3






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CTXQUERY Forms Sample Application

This chapter presents the CTXQUERY sample application, developed with Oracle Forms 4.5, and illustrates one method for developing applications using ConText.

The topics covered in this chapter are:

Overview of CTXQUERY

The CTXQUERY sample application is a basic Oracle Forms 4.5 application which provides a graphical interface for performing text queries and DML operations with ConText. It supports all the query expression operators and can provide query term highlighting using asterisks in the specified documents.


The CTXQUERY sample Forms application does not utilize any of the theme querying functionality provided by ConText. However, the sample application could be theme-query enabled for English-language documents simply by creating a theme indexing policy, indexing the column with the policy, and referencing the policy in the query block.



The ConText query concepts demonstrated in this example are:


The form is laid out in four blocks on three canvases. There is a block and a canvas for each step of the query, hitlist, and view with one extra block for all the buttons. All canvases are displayed in a single window, CTXQUERY.

Setting Up the Sample

This sections provides information about the setup tasks that must be performed before using the sample application:

Demonstration Installation Scripts

Before the sample Forms application can be used, the demonstration installation scripts must be run. The demonstration installation scripts are provided with ConText and are installed automatically on the server machine during ConText installation; however, they must be run manually after ConText is installed.

The demonstration scripts perform the following tasks:

Oracle Forms Installation

The sample application requires Oracle Forms (32-bit), version or higher, to be installed.

Oracle Forms is not installed automatically during ConText Workbench installation and must be installed manually before using the sample application.


If a version higher than is installed on your machine, to use the sample application, the ctxquery.fmb file may have to be regenerated after installation.


CTXQUERY Architecture

The CTXQUERY form is divided into eight distinct sections:


On startup, the When-New-Form-Instance trigger initializes the form.

  set_window_property('CTXQUERY', WINDOW_STATE, MAXIMIZE);
  select query_id.nextval 
    into :global.query_id
    from dual;

This maximizes the windows for display, then selects a query ID from a sequence.

This form is designed so that it can be used by multiple concurrent users, which means that the results tables are shared. When result tables are shared, a unique query ID separates each user's results from other users. In this form the unique ID is created as an increasing sequence of numbers with the last value stored in a global variable.

Enter the query screen

The query screen is the first screen of the form displayed.

Each widget is part of the query block, which is a non-base-table block. There is one hidden field in this screen, query_string.

When the Query button is pressed, the When-Button-Pressed trigger goes to the hitlist block and executes a query:

When-Button-Pressed on BUTTONS.QUERY


The hitlist block is based on the article_hitlist view. This view joins the query result table query_temp and the base table articles into a hitlist which has both score and article information. Although this block contains items for all the fields in this view, most are hidden. The visible page displays score, author, section, and title.

Start the pre-query trigger

Before the query on the hitlist block is executed, the pre-query trigger fires. This trigger executes the first step of a two-step query, then limits the relational fields to the query criteria:

Pre-Query on HITLIST


--limit the relational fields to the query criteria
-- :hitlist.conid := :global.query_id; :=; :hitlist.section := :query.section; copy(:query.pub_date,'hitlist.pub_date');

Build the query expression

The build_query_string procedure constructs the query expression by concatenating the term, weight, and operator fields from the form and putting them into the query.query_string hidden field.

build_query_string is divided into sections A through E.

Section A

Section A of the code clears the query string of any previous contents.

Section B

Section B takes each term from the user input form and builds the query expression as follows:

Section C

Section C of the code strips off extraneous operators at the end of the final query string since the last term has no boolean operator.

Section D

Section D adds the score threshold value to the query expression.

Section E

Section E appends the result limit.

BUILD_QUERY_STRING Procedure - Sample Code

PROCEDURE build_query_string IS
--Section A
    :query.query_string := null;
--Section B
    if (:query.qterm1 is not null) then
      :query.query_string := :query.query_string ||
        :query.qexp1 ||
        '{' || :query.qterm1 || '}' ||
        '*' || to_char(nvl(:query.qwt1, 1)) ||
    end if;
if (:query.qterm2 is not null) then
    :query.query_string := :query.query_string ||
      :query.qexp2 ||
      '{' || :query.qterm2 || '}' ||
      '*' || to_char(nvl(:query.qwt2, 1)) ||
end if;
if (:query.qterm3 is not null) then
    :query.query_string := :query.query_string ||
      :query.qexp3 || 
      '{' || :query.qterm3 || '}' ||
      '*' || to_char(nvl(:query.qwt3, 1));     
end if;
--Section C
:query.query_string := 
rtrim(:query.query_string, '&|,;-');
--Section D
    if (:query.qthresh is not null) then
        :query.query_string := '(' || :query.query_string ||
        ')>' || to_char(:query.qthresh);
    end if;
--Section E
    if (:query.qlimit is not null) then
        :query.query_string := '(' || :query.query_string ||
        '):' || to_char(:query.qlimit);
    end if;

Display an article in the view block

When an article in the hitlist is double-clicked, the When-Mouse-Double-Click trigger on hitlist.title displays the article in the VIEW block:

When-Mouse-Double-Click on HITLIST.TITLE

In order to display the correct article, the Pre-Query trigger limits the view block to display the article highlighted in the hitlist block:

Pre-Query on VIEW:
:view.article_id := :hitlist.article_id;

The view block is based on articles, and displays the full text of the article.

Invoke the HIGHLIGHT procedure

When the highlight button on the view block is pressed, the When-Button-Pressed trigger on buttons.highlight invokes the CTX_QUERY.HIGHLIGHT procedure.

The highlight procedure is divided into sections A and B.

Section A

Section A call the HIGHLIGHT procedure and performs the following tasks:

The highlight result table (highlight_temp) has the following structure:

Columns   TYPE  









This procedure highlights matching query terms in the text window by surrounding them with <<< and >>>.

It is not possible to do an INSTR for the search terms because of the expansion operators; for example, go=going=gone in a stem expansion. Instead, use the highlight procedure in Section A to generate the highlights table.

This table holds the offset and the length of each word to be highlighted.

Section B

With the highlights generated, the cursor loop in Section B works through each offset, length pair backwards from last offset to first.

The asterisks insert won't change the other offsets. For each offset, length pair, the asterisks are inserted by reassigning the full text to: everything before the term (line 1), then the asterisks, then the term and some more asterisks (line 2) then everything after the term (line 3). Doing this repeatedly highlights all the terms in the document.

HIGHLIGHT Procedure -- Sample Code

PROCEDURE highlight IS 
  cursor highcur is select offset, length
    from highlight_temp
    where id = :global.query_id
    order by offset desc;
--  Section A
    'DEMO_POLICY',              -- policy name
    to_char(:view.article_id),  -- textkey 
    :query.query_string,        -- query string 
    :global.query_id,           -- query_id 
    'HIGHLIGHT_TEMP',           -- highlight table
--  Section B
  for hc in highcur loop
1.    :view.text := substr(:view.text,1,hc.offset - 1) ||
2.    '***'||substr(:view.text,hc.offset,hc.length)||'***'||
3.    substr(:view.text,hc.offset+hc.length);
  end loop;

Perform DML Operations

When a document is changed it needs to be re-indexed and new linguistic information needs to be extracted. This can be performed in a table trigger or in the application.

The view block contains pre-update and pre-index triggers that perform the necessary re-indexing when there is a change to article data. Both triggers invoke the reindex_article procedure.

The reindex_article procedure performs the following tasks:

REINDEX_ARTICLE Procedure -- Sample Code

PROCEDURE reindex_article IS
  handle number;
# Section A
ctx_dml.reindex('demo_policy', TO_CHAR(:view.article_id));
# Section B
delete from article_themes
where pk = :view.article_id;

delete from article_gists
where pk = :view.article_id;
# Section C
Section D
  handle := ctx_ling.submit(0,FALSE,0);


Before the session is ended, clean up any leftover rows in the hitlist result table (query_temp) and the highlight result table (highlight_temp) tables for the query ID:

delete from query_temp 
where conid = to_number(:global.query_id);
delete from highlight_temp
where id = to_number(:global.query_id);

The standard.commit statement executes an Oracle COMMIT without doing a Forms commit_form.


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