Oracle Context Option Application Developer's Guide

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CHAPTER 9. CTXQUERY - Forms Sample Application

Overview of CTXQUERY
CTXQUERY Form Architecture

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

The topics covered in this chapter are:

Overview of CTXQUERY

CTXQUERY Form Architecture

Overview of CTXQUERY

The CTXQUERY sample Forms application is a simple Oracle Forms 4.5 application which allows GUI text querying and DML operations. It supports all the query expression operators and can provide text query term highlighting using asterisks in the specified documents.

Note: The CTXQUERY sample Forms application does not utilize any of the theme querying functionality provided by ConText Option.

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.

For more information about theme queries and theme indexing policies, see "Theme Queries (Chapter 4)".

Distribution and Usage

CTXQUERY (runtime and source code) is distributed with Oracle ConText Option Workbench. Oracle ConText Option Workbench can be installed on any personal computer running the Windows environment.

Before the sample form can be used, the demonstration installation scripts must be run. The demonstration installation scripts are provided with ConText Option and are installed automatically on the server machine during ConText Option installation.

For more information about running the demonstration installation scripts, see the Oracle7 Server installation documentation specific to your operating system.

Concepts

The ConText Option concepts demonstrated in this example are:

query expression syntax

boolean and statistical (logical) operators

expansion operators

score thresholds

result limits

two-step queries

sharing result tables

term highlighting

Layout

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.

CTXQUERY Form Architecture

The architecture for the CTXQUERY form can be divided into eight distinct sections:

startup

enter the query screen

start the pre-query trigger

build the query expression

display an article in the view block

invoke the HIGHLIGHT procedure

perform DML operations

cleanup

Startup

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

  When-New-Form-Instance

  set_window_property
	(FORMS_MDI_WINDOW, WINDOW_STATE, MAXIMIZE);
  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

	go_block('hitlist');
	clear_block(no_validate);
	execute_query(all_records);

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

	build_query_string;

	ctx_query.contains('DEMO_POLICY',
					:query.query_string,
					'QUERY_TEMP',
					1,
					:global.query_id,
					0,1,null);

	--
	--	limit the relational fields to the query criteria
	--

	:hitlist.conid := :global.query_id;
	:hitlist.author := :query.author;
	: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:

attaches expansion operators (FUZZY, STEM, SOUNDEX) to the front of each specified query term

encases user-specified query arguments in curly brackets

Query arguments are enclosed in curly brackets so that any special characters within the argument (e.g., the "&" in Q&A) will not be misinterpreted as ConText operators

adds weighting factor

If the user has filled in a weighting factor in the appropriate field of the input screen, this value is appended to the search argument.

appends any specified logical operators to the end of the query expression

Note: Logical operators are Boolean operators that join terms together.

When the concatenation is finished, a sample term looks like this:

! {cat} *2 &

expansion search weight boolean operator criteria operator Note: In CTXQUERY, the user can enter up to three separate query expression. These four steps are repeated to for each query expression.

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
BEGIN

--
--	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)) ||
			substr(:query.qop1,2,1);

	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)) ||
		substr(:query.qop2,2,1);

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;

END;

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

	GO_BLOCK('VIEW');
	EXECUTE_QUERY;

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:

fetches the document

parses the query

identifies the matching terms

inserts results into the HIGHLIGHT_TEMP table.

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

TABLE HIGHLIGHT_TEMP
COLUMNS ID NUMBER
OFFSET NUMBER
LENGTH NUMBER
STRENGTH NUMBER

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
--

BEGIN
	ctx_query.highlight( 
		'DEMO_POLICY',			-- policy name
		to_char(:view.article_id),	-- textkey 
		:query.query_string,		-- query string 
		:global.query_id,			-- query_id

		null,
		null,
		'HIGHLIGHT_TEMP',			-- highlight table
		null,
		null,
		null,
		null);

--
--	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;
END;

Perform DML Operations

When a document is changed it needs to be reindexed 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 reindexing when there is a change to article data. Both triggers invoke the REINDEX_ARTICLE procedure.

The REINDEX_ARTICLE procedure performs the following tasks:

submits the document for text reindex (Section A)

clears existing linguistic information (Section B)

extracts new linguistic information (Section C)

submits the linguistic requests (Section D)

Note: There is no COMMIT; it is performed by the COMMIT of the change to the VIEW block. In SUBMIT, you must explicitly ask for it not to COMMIT (the FALSE second parameter).

For more information about DML and reindexing, see Oracle ConText Option Administrator's Guide.

REINDEX_ARTICLE Procedure -- Sample Code

PROCEDURE reindex_article IS

	handle number;

begin

#
#	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
#

ctx_ling.REQUEST_themes('demo_policy',
					TO_CHAR(:view.article_id),
						'article_themes');

ctx_ling.REQUEST_gist('demo_policy',
					TO_CHAR(:view.article_id),
						'article_gists');

#
#	Section D
#

	handle := ctx_ling.submit(0,FALSE,0);
end;

Cleanup

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:

	Post-Form

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

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

	standard.commit;

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

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`TABLE`	`HIGHLIGHT_TEMP`
`COLUMNS`	`ID`	`NUMBER`
	`OFFSET`	`NUMBER`
	`LENGTH`	`NUMBER`
	`STRENGTH`	`NUMBER`