Overview: Adjusting How Screens are Identified

Active host screens viewed in Presentation Designer must be identified programmatically by traits that remain constant, regardless of the data being displayed. The correct form must display for a previously visited screen, and new forms must generate for screens visited for the first time.

When you navigate to a new host screen at design time, a default screen recognition rule is automatically generated.

A screen recognition rule consists of a logical statement, whose job it is to identify a unique host screen during run time; the logical statement is composed of sub rules. The sub rules identify the characteristics of the fields and data on the screen.

How a Screen Recognition Rule Works

By default, when a screen is downloaded from the host, its format is compared to the screen recognition rules of all the known screens. If it evaluates as true, the appropriate form is displayed.

If a host screen meets
This occurs
All of the requirements of a screen recognition rule The appropriate form is displayed.
The requirements of several screen recognition rules The first form with which it is a complete match is displayed.
None of the requirements for any screen recognition rule, and no match is found before the time out concludes
  • During design time, a new default recognition rule is created and a new form is generated.

  • During run time, you can direct the user to an error form that you've specified.
Note Screens that appear identical can actually be very different. A single field, misplaced by only one character position, can cause a screen recognition rule to evaluate as false.

Often, comparing the screen recognition rules for both screens will help you quickly identify their differences.

Modifying Screen Recognition Rules

The screen recognition rules provide you with a great deal of freedom and flexibility for customizing your application. The main reasons for modifying screen recognition rules are to:

Related Topics
Bullet Customizing Individual Screens
Bullet Comparing Host Screens and Screen Recognition Rules
Bullet Distinguishing Between Screens Recognized as the Same
Bullet Making Screens Recognized as Different the Same
Bullet Creating and Editing User Fields