# CHAPTER 1: Introduction

## 1.1 What is Empress 4GL?

Empress 4GL is an application development environment containing a fundamental programming language and a set of tools to help you develop your application quickly.

The Empress 4GL language is an event-driven language which uses the following basic structures as building blocks to construct complex applications which may be used as prototypes or finished products.

- Forms
- Windows
- Fields
- Keys
- Scripts

The Empress 4GL development tools consist of:

- Default Application Generator
- Application Generator
- Application Manager
- Form Manager
- Source Debugger
- Executable Builder
- Compiler
- Linker

## 1.2 Capabilities of Empress 4GL

Using Empress 4GL you can design and run applications that may access Empress databases. Your application may be simple, allowing you to retrieve information from a single database table, or it may be sophisticated, accessing several databases and processing the data in complex ways. In addition, an application can act as a menu interface to the operating system and to Empress database.

Empress 4GL offers several advantages as a design environment. It is easy to use, it improves productivity, and your applications will be easy to maintain and enhance. It is particularly useful for the development of screen-intensive applications. The facilities for screen control that you will be using are centered on two powerful concepts: screen painting and windowing.

- Screen painting is the ability to design a screen format by simply painting it directly on the screen. When the application is run, the screen format will appear just as it was painted. This means that you need not do any programming to position things where you want them.

- Windowing is a technique for dividing the screen into independent regions so that you can see and do different things in the different regions. Each region is called a window and shows a format you have painted. Windows can be programmed to appear when required, become larger or smaller at the touch of a key, or even to move around.

If you wish to use Empress 4GL to do simple Query Language operations on a database table, you can generate a default application for the table of your choice. Empress 4GL will create an application that will allow you to select, update, delete and insert records in the table.

If you wish to design a more sophisticated application, Empress 4GL provides a simple language with which you can write scripts to do the processing you require. With scripts, you can access tables in databases, do computations and comparisons on the data, create and control windows, and effectively do anything you could do with another programming language.

## 1.3 Features of Empress 4GL

The programming language of Empress 4GL is used to write scripts that allow the application to respond to user or system events. Some example are: pressing a function key, moving between fields in a window, and responding to errors and operating system signals.

Empress 4GL provides:

- Commands to select, insert, update and delete records from database tables. Additionally, there are commands to define and set variables, evaluate expressions, perform iterative processing, conditional testing and comparison operations.

- Convenient and efficient screen handling functions that allow you to define windows which you can display and remove from the screen with single commands.

- A convenient means of attaching scripts to function keys, so that users of your application can control windows and processing with a minimum number of keystrokes.

- A series of functions designed to facilitate the programming