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# How OSAS Does GUI

Windows-based applications written in languages like Visual Basic® use object oriented programming. In this programming method, the objects or controls placed on a form (as well as the form itself) contain code that is executed when events involving the control occur (such as gaining or losing focus).

OSAS code is written in a top-down structure, meaning that the code is essentially executed from beginning to end, and is not tied to specific fields or events. Each of these coding structures has advantages and disadvantages.

The goal of Open Systems in developing the graphical interface was to provide users with a consistent, familiar keyboard interface and in-line field verification while adding graphical features, mouse navigation and Windows functionality. The result is a Windows interface that maintains its ties to the existing product while providing a new look and feel.

In order to make use of the existing OSAS code, graphical events must be captured, interpreted, and simulated within the existing OSAS code structure.

So that your applications maintain a standard Windows interface, you must take great pains to assure that the rules of graphical interfaces are adhered to wherever possible as you convert your programs to graphical.