Fourthgeneration languages visual languages

Fourth-generation languages (4GL) provide a higher level of abstraction than third-generation languages in that they support visual program development. With visual programming, the programmer has the ability to create graphical user interfaces by pointing and clicking with a mouse, similar to using the Windows operating system. This contrasts with third-generation programming where the programmer has to write code with the keyboard. 4GLs are a product of the visual programming age that began with the rise of the GUI operating systems such as Windows. 4GLs have many recognised features including:

♦ Rapid development of applications compared to 3GLs

♦ Visual environment for development

♦ Built-in 3GL language support

♦ Faster learning curve

Visual Basic, and even VBA for Excel to a certain extent, is a 4GL that evolved from Microsoft Basic which was used on the first-generation microcomputers. With Visual Basic, programs are created in an Integrated Development Environment (IDE). The IDE provides a means of producing programs in a fraction of the time it would take using a 3GL. Delphi is another fourth-generation Windows programming language that was developed by the Borland company in the early 1990s. Delphi evolved from a very successful DOS version of Pascal, called Turbo Pascal, developed in 1984. 3GL language support is an essential feature of a 4GL as the developer can only do so much with the 4GL visual layer. The Delphi visual programmer's interface is shown in Figure 1.8, and is similar to that used in Visual Basic. The illustration displays a Form that the developer can drop components onto as the means of developing the application. The important point to make is that although this can be achieved visually, the developer will often have to program at the 3GL level, as we will see in Chapter 10. The main difference between Visual Basic and Delphi is that the former is an interpreted language. An interpreted language translates source code line by line; by contrast Delphi is a compiled 4GL, which means the code is completely translated into machine language before execution. Therefore, the program will run faster if compiled. Both Visual Basic and Delphi are Rapid Application Development (RAD) languages.

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