Fourt Generation Language:-
A fourth-generation programming language (1970s-1990) (abbreviated 4GL) is a programming language or programming environment designed with a specific purpose in mind, such as the development of commercial business software. In the evolution of computing, the 4GL followed the 3GL in an upward trend toward higher abstraction and statement power. The 4GL was followed by efforts to define and use a 5GL.
The natural-language, block-structured mode of the third-generation programming languages improved the process of software development. However, 3GL development methods can be slow and error-prone. It became clear that some applications could be developed more rapidly by adding a higher-level programming language and methodology which would generate the equivalent of very complicated 3GL instructions with fewer errors. In some senses, software engineering arose to handle 3GL development. 4GL and 5GL projects are more oriented toward problem solving and systems engineering.
All 4GLs are designed to reduce programming effort, the time it takes to develop software, and the cost of software development. They are not always successful in this task, sometimes resulting in inelegant and unmaintainable code. However, given the right problem, the use of an appropriate 4GL can be spectacularly successful as was seen with MARK-IV and MAPPER (see History Section, Santa Fe real-time tracking of their freight cars - the productivity gains were estimated to be 8 times over COBOL). The usability improvements obtained by some 4GLs (and their environment) allowed better exploration for heuristic solutions than did the 3GL.

History
Though used earlier in papers and discussions, the term 4GL was first used formally by James Martin in his 1982 book Applications Development Without Programmers to refer to non-procedural, high-level specification languages. In some primitive way, IBM's RPG (1960) could be described as the first 4GL followed closely by others, such as the Informatics MARK-IV (1967) product and Sperry's MAPPER (1969 internal use, 1979 release).

The motivations for the '4GL' inception and continued interest are several. The term can apply to a large set of software products. It can also apply to an approach that looks for greater semantic properties and implementation power. Just as the 3GL offered greater power to the programmer, so too did the 4GL open up the development environment to a wider population.

In a sense, the 4GL is an example of 'black box' processing, each generation (in the sense of the page) is further from the machine (see the Computer Science history in regard to data structure improvements and information hiding). It is this latter nature that is directly associated with 4GL having errors that are harder, in many cases, to debug. In terms of applications, a 4GL could be business oriented or it could deal with some technical domain. Being further from the machine implies being closer to domain. Given the wide disparity of concepts and methods across domains, 4GL limitations lead to recognition of the need for the 5GL.

Types

* Report generators take a description of the data format and the report to generate and from that they either generate the required report directly or they generate a program to generate the report.
* Similarly, forms generators manage online interactions with the application system users or generate programs to do so.
* More ambitious 4GLs (sometimes termed fourth generation environments) attempt to automatically generate whole systems from the outputs of CASE tools, specifications of screens and reports, and possibly also the specification of some additional processing logic.
* Data management 4GLs such as SAS, SPSS and Stata provide sophisticated commands for data manipulation, file reshaping,case selection and data documentation in the preparation of data for statistical analysis and reporting.

Some 4GLs have integrated tools which allow for the easy specification of all the required information:

* James Martin's own Information Engineering systems development methodology was automated to allow the input of the results of system analysis and design in the form of data flow diagrams, entity relationship diagrams, entity life history diagrams etc from which hundreds of thousands of lines of COBOL would be generated overnight.
* More recently Oracle Corporation's Oracle Designer and Oracle Developer 4GL products could be integrated to produce database definitions and the forms and reports programs.