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The primary purpose of the DATA statement is to give names to
constants; instead of referring to pi as 3.141592653589793 at every
appearance, the variable PI can be given that value with a DATA
statement and used instead of the longer form of the constant.
This
also simplifies modifying the program, should the value of pi change.
-- FORTRAN manual for Xerox Computers |
Software is created by programmers using programming languages. These are formalised languages with precise rules of usage, or syntax. There are many such languages, ranging from the fairly elementary and easy-to-learn BASIC (Beginner's All-purpose Symbolic Instruction Code) to the more sophisticated object-oriented C++.
The various languages have different strengths and characteristics, making them suitable for particular kinds of applications. For instance, FORTRAN (Formula Translation) is oriented towards numerical calculations and is widely used in the scientific community. Perl (Practical Extracting and Reporting Language) excels in textual pattern-matching and is very popular for web applications involving character data.
Compiled programs written in languages such as FORTRAN and C or C++ aren't directly executable by a computer; they are translated into lower-level machine language by compilers and then are executed directly by the hardware. Interpreted programs written in languages such as Perl and Java are translated and executed by an interpreter each time the program is run.
Software Engineering
Software has become very feature-rich and complex, and the task of developing reliable programs that perform correctly and efficiently, has become very difficult and expensive. The so-called 'Y2K' problem, or millenium bug, is a well-known example of the kind of problem that can occur (storing only the last 2 digits of the year on the assumption that the program wasn't going to last till the year 2000).
Some programs can contain millions of lines of code, and exceed any individual's ability to comprehend them. Software engineering is the discipline of creating manageable and correct software, using techniques such as object-oriented design and programming (OOD, OOP). These techniques seek to compartmentalise software into discrete object-like units that can be well-understood independently, and combined as building blocks to make large software systems.
Object-Oriented Design and Programming
Object-oriented programming is a method of implementation in which programs are organized as cooperative collections of objects, each of which represents an instance of some class, and whose classes are all members of a hierarchy of classes united via inheritance relationship.
