35 Introduction To 4gl

Introduction

INFORMIX-4GL is a fourth-generation programming language that is used for the development of database applications with a character-based interface.

INFORMIX-4GL provides all the standard constructs of third-generation languages plus two data structures:

• Record: Collection of members in which each member can have any valid Informix data type
• Array: Data structure of up to three dimensions of values of the same data type.

Compiled or Rapid Development System

Two versions:

• INFORMIX-4GL: Compiled version
• INFORMIX-4GL Rapid Development System (RDS): Interpreted version

The Process of Creating Programs

1. Design your program
2. Create an ASCII file for each screen form
3. Compile each form
4. Create an ASCII file for each source code module
5. Compile each module
6. Define and compile the complete program
7. Test, debug and correct both syntax and logic.

Suffix	Contents
per	Form source code
4gl	Module source code
err	Error file for both forms and modules
frm	Compiled screen form
4go	Interpreted module p-code
o	Compiled module object
4gi	Interpreted program p-code
4ge	Compiled program
c	C code source equivalent to 4GL source
ec	intermediate C source fiel
erc	Object error
pbr	Form source code backup
fbm	Form object backup
4bl	Module source code backup
4bo	Object backup
4be	Program backup
4db	Debugger initialization file

The Development Environment

Two interfaces:

• Menu-Driven Environment: Command i4gl
• The Command-Line Environment: Command form4gl

The Debugger: Command fgldb

Basic Language Features

Comments: # or with —.
Multiple lines comment: { }

User Interaction

• Window: Name rectangular area on the terminal screen
• Forms: Collection of labels and input fields in which the user can input or edit information that is stored in memory on program variables.
• Menus: Menus provide users with a list of actions that, once selectedm perform the task represented by the choise.

Programming Blocks

Types:

• MAIN: only one MAIN block
• FUNCTION
• REPORT

Standard Language Constructs

• Definitions and Declarations: DEFINE, FUNCTION, MAIN ,REPORT
• Flow of Control: CALL, CASE, CONTINUE, END
• 4GL Compiler Directives: DATABASE, DEFER, GLOBALS, WHENEVER
• Storage Management: INITIALIZE, LET, LOCATE, VALIDATE

Screen I/O Language Constructs

The INFORMIX-4GL command set includes a collection of statements designed to facilitate screen and keyboard interactions