Flow of Control in WDB.

The actual flow of control is perhaps better illustrated in the following diagram :

 
Figure 4: Flow of Control 

What happens is the following

• The users "clicks" on a URL leading to the WDB script. The URL contains some extra information in the path (PATHINFO), specifying what information in the database s|he would like to query. This is typically obtained from a normal hypertext page with a menu of available query forms.

• The server receives the URL, starts the WDB script and passes the extra information in PATHINFO, actually the name of the Form Definition File (fdf\) to use and the word "form".

• WDB reads the fdf and generates an HTML form according to the specifications in the fdfThe form is returned to the user and WDB exits.

• The user fills out the form with her query constraints and presses the "Submit" button. This sends the WDB URL (with PATHINFO) plus the contents of the form (encoded) to the WWW Server.

• The server receives the URL, starts the WDB script and passes the extra information in PATHINFO plus the form content.

• WDB parses the PATHINFO which in this case is the name of the fdf plus the word "query". This tells WDB to construct a SQL query from the information in the fdf file and and the user's constraints.

• The SQL query is send to the database server.

• The database server processes the query and returns a number of rows.

• WDB retrieves the rows from the database server and after having converted the data according to the specifications in the fdfconstructs an HTML page with the result. If more than one row was returned, a tabular output format is chosen, allowing the user to select a row, via a hypertext link, to get all the details.

• The HTML page is returned to the user and WDB exits.

• The user clicks on a hypertext link for a row. This link contains the WDB URL with the fdf name, the word "query" and the key(s) for the current row in the PATHINFO.

• The WWW server receives the URL, starts the WDB script and passes it the extra information in PATHINFO.

• WDB constructs a new database query, this time using the key(s) instead of the form contents.

• The database process the query and returns the result.

• WDB retrieves the row from the database server, converts the data according to the specifications in the fdf and this time, as only one row is returned, constructs a HTML page with all the details. The HTML page is returned to the user and WDB exits.

• etc.