Generations of Programming Languages

In order to write a program a suitable programming language must be chosen. A program is a set of instructions written in a particular programming language. Which when executed will produce a solution to a given problem or perform a specified task. The main difference between an algorithm and a program is that an algorithm can be written in informal language without having to follow special rules whereas the program is written in a programming language and must follow all the syntax rules of the language.

A program written in Pascal is referred to as a source program or source code, because Pascal is a high level language. However computers are built to execute instructions written in what is called machine language. In machine language everything is expressed in terms of the binary number system – 1’s and 0’s. Machine language is considered a low level programming language.

Generations of programming languages

Many programming languages have been developed throughout the years. These languages are classified into different generations.

In the 1940’s and 1950’s programs written in the first generation language consist of a series of ones and zeroes. Such programs are referred to as machine language programs. This language is the lowest computer language. Machine language programs have instructions that are similar to the following

01010101 01110001

10011000 11110000

00101010 10010101
Machine language is considered a low- level programming language.
Characteristics of 1GL

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  Fastest to execute because it is already in a language that the computer can understand
  
• 
  Difficult to decipher
  
• 
  Easy to make mistakes
  
• 
  Time consuming and tedious to write
  
• 
  Machine dependent
  

Advantages

• 
  Machine language programs are the fastest programs when being executed
  

• 
  It is time consuming to write.
  
• 
  It is easy to make a mistake because only 0’s and ones are used.
  
• 
  Programs written for one type of computer cannot be used on another kind of computer. They are machine dependent.
  

Second generation language is called assembly language.

Assembly language programs use short codes or mnemonics to represent instructions e.g. ADD, SUB. This was closely related to machine language but it allowed the programmer to use instruction codes as described above and names for storage locations rather than strings of binary digits.

Assembly language codes came in the mid 1950's, the second generation of programming language like AUTOCODER, SAP and SPS. Symbolic addresses allowed programmers to represent memory locations, variables and instructions with names. Programmers now had the flexibility not to change the addresses for new locations of variables whenever they are modified. This kind of programming is still considered fast and to program in machine language required high knowledge of the CPU and machine's instruction set. This also meant high hardware dependency and lack of portability. Assembly or machine code could not run on different machines. Example, code written for the Intel® Processor family would look very different for code written for the Motorola 68X00 series. To convert would mean changing a whole length of code.

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  Assembly language programs are easier to write than machine language programs.
  
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  Can be easily converted to machine code by a program called an assembler.
  

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  It was very tedious and error prone
  
• 
  It forced the programmer to think in terms of the machine( the CPU and the amount of memory and the instruction set) rather than in terms of the problem i.e. the programming language is machine dependent
  
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  Therefore a program written for one computer could not necessarily be run on another computer
  

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  Easier to write than machine language
  
• 
  Machine dependent
  

Throughout the early 1960's till 1980 saw the emergence of the third generation programming languages. The third generation programming languages are known as high level languages. High level languages are not machine dependent. The programmer does not have to think of the machine but can concentrate on solving the problem. They use English -like statements and are therefore easier to write. E.g. COBOL, FORTRAN, Pascal, Basic and C.

• 
  It uses English –like statements
  
• 
  It is not machine dependent
  

Disadvantage

• is that they have to be converted into machine language.

Advantages

• They provide support for ideas of abstraction so that programmers can concentrate on finding the solution to the problem rapidly, rather than on low-level details of data representation.

• Although the syntax between these languages were different but they shared similar constructs and were more readable by programmers and users compared to assembly languages.

• Third generation languages support procedural languages, which means that the program will execute a sequence of instructions in a specific order.

Name	Purpose
COBOL	To solve business problems such as inventory control accounts and any problems involving processing large volumes of data. Business, finance and administrative systems.
FORTRANIt was designed to allow easy translation of math formulas into code.	To solve problems that involve complex mathematics, scientific problems, and engineering problems.
Pascal	To assist in the teaching of programming concepts but can also be used for solving business problems
Basic	To solve mathematical and business problems
C	To write operating system programs and business software. It is a general purpose language

Fourth Generation

Fourth generation languages are easier to write than any of the earlier generations. They are non- procedural. In a nonprocedural language, users define only what they want the computer to do, without supplying all the details of how something is to be done. They use English like statements and are very user friendly. Often abbreviated 4GL, fourth-generation languages are programming languages closer to human languages than typical high-level programming languages. Most 4GLs are used to access databases. For example, a typical 4GL command is FIND ALL RECORDS WHERE NAME IS "SMITH"

4GL, or "report generator language" are "application specific" languages, with built-in knowledge of an application domain in the way that SQL has built-in knowledge of the relational database domain. The term was invented by Jim Martin to refer to non-procedural high level languages built around database systems. Fourth generation languages are close to natural language and were built with the concept that certain applications could be generalized by adding limited programming ability to them. When given a description of the data format and the report to generate, a 4GL system produces COBOL (or other 3GL) code, that actually reads and processes the data and formats the results. Some examples of 4GL are: database query language e.g. SQL; Focus, Metafont, PostScript, S, IDL-PV, WAVE, Gauss, Mathematica, and data-stream languages such as AVS, APE, Iris Explorer. Microsoft Visual Basic, Visual Fox Pro.

High-level computer language (such as IBM's Structured Query Language or SQL) that allows non-programmer users to write (usually short) programs to query databases and to generate custom reports.

Advantage: useful for generating reports and are user friendly

Disadvantage: Can become very wordy and they are slow

Characteristics of 4GL

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  Uses English like statements that are more user friendly
  
• 
  This reduces the time taken to write
  
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  They contain built in function wizards to assist the user in solving the problem
  

They fall into the following categories

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  Database query language -SQL
  
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  Report generators –Oracle
  
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  GUI creators – Visual basic
  
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  Screen painters and generators – oracle forms
  
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  Data manipulation, analysis and reporting languages - Focus
  

Fifth generation languages

The 1990's saw the developments of fifth generation languages like PROLOG. 5GL’s are used mainly in artificial intelligence. 5GL’s are non procedural languages. Essentially 5Gl’s are 4GL’s with a knowledge base. The main difference between 4GL’s and 5GL’s is that 4GL’s are designed to build specific programs whereas 5GL’s are designed to make the computer solve the problem for you. The programmer only needs to be concerned with the problem and the constraints or the conditions to be met for that particular problem. All codes for the 5GL’s are automatically generated. It uses a visual or graphical development interface to create a program that is usually compiled with a 3GL compiler. Examples of 5GL’s are OPS5 (Official Production System), Prolog (Logical Programming) and Mercury.

Advantages

• 
  Computers will be able to communicate in natural spoken language.
  

Disadvantages

• 
  Very complex to design, programmer must be highly trained
  

Exercise

1. 
   What is a computer program?
   
2. 
   Give three examples of high level languages and the kind of processing for which they were designed.
   
3. 
   Name two characteristics of Two of the following:
   

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  Machine language
  
• 
  Assembly language
  
• 
  High level language
  

4. 
   Low level languages programs are more difficult to write than high level language programs. State two reasons for this.
   

5. 
   State the programming language that is associated with:
   

1. 
   Artificial intelligence
   
2. 
   Business applications
   
3. 
   Operating systems
   
4. 
   Scientific problems
   

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