Modern Computing-Quality requirements

Quality requirements

Whatever the approach to software development may be, the final program must satisfy some fundamental properties. The following five properties are among the most relevant:

• Efficiency/Performance: the amount of system resources a program consumes (processor time, memory space, slow devices, network bandwidth and to some extent even user interaction), the less the better.
• Reliability: how often the results of a program are correct. This depends on prevention of error propagation resulting from data conversion and prevention of errors resulting from buffer overflows, underflows and zero division.
• Robustness: how well a program anticipates situations of data type conflict and other incompatibilities that result in run time errors and program halts. The focus is mainly on user interaction and the handling of exceptions.
• Usability: the clarity and intuitiveness of a programs output can make or break its success. This involves a wide range of textual and graphical elements that makes a program easy and comfortable to use.
• Portability: the range of computer hardware and operating system platforms on which the source code of a program can becompiled/interpreted and run. This depends mainly on the range of platform specific compilers for the language of the source code rather than anything having to do with the program directly.

Algorithmic complexity

The academic field and the engineering practice of computer programming are both largely concerned with discovering and implementing the most efficient algorithms for a given class of problem. For this purpose, algorithms are classified into orders using so-called Big O notation,O(n), which expresses resource use, such as execution time or memory consumption, in terms of the size of an input. Expert programmers are familiar with a variety of well-established algorithms and their respective complexities and use this knowledge to choose algorithms that are best suited to the circumstances.

Methodologies

The first step in most formal software development projects is requirements analysis, followed by testing to determine value modeling, implementation, and failure elimination (debugging). There exist a lot of differing approaches for each of those tasks. One approach popular forrequirements analysis is Use Case analysis.

Popular modeling techniques include Object-Oriented Analysis and Design (OOAD) and Model-Driven Architecture (MDA). The Unified Modeling Language (UML) is a notation used for both OOAD and MDA.

A similar technique used for database design is Entity-Relationship Modeling (ER Modeling).

Implementation techniques include imperative languages (object-oriented or procedural), functional languages, and logic languages.

Measuring language usage

It is very difficult to determine what are the most popular of modern programming languages. Some languages are very popular for particular kinds of applications (e.g., COBOL is still strong in the corporate data center, often on large mainframes, FORTRAN in engineering applications, and C in embedded applications), while some languages are regularly used to write many different kinds of applications.

Methods of measuring language popularity include: counting the number of job advertisements that mention the language^[7], the number of books teaching the language that are sold (this overestimates the importance of newer languages), and estimates of the number of existing lines of code written in the language (this underestimates the number of users of business languages such as COBOL).

Debugging

A bug which was debugged in 1947.

Debugging is a very important task in the software development process, because an incorrect program can have significant consequences for its users. Some languages are more prone to some kinds of faults because their specification does not require compilers to perform as much checking as other languages. Use of a static analysis tool can help detect some possible problems.

Debugging is often done with IDEs like Visual Studio, NetBeans, and Eclipse. Standalone debuggers like gdb are also used, and these often provide less of a visual environment, usually using a command line.

Programming languages

Main articles: Programming language and List of programming languages

Different programming languages support different styles of programming (called programming paradigms). The choice of language used is subject to many considerations, such as company policy, suitability to task, availability of third-party packages, or individual preference. Ideally, the programming language best suited for the task at hand will be selected. Trade-offs from this ideal involve finding enough programmers who know the language to build a team, the availability of compilers for that language, and the efficiency with which programs written in a given language execute.

Allen Downey, in his book How To Think Like A Computer Scientist, writes:

The details look different in different languages, but a few basic instructions appear in just about every language:

• input: Get data from the keyboard, a file, or some other device.
• output: Display data on the screen or send data to a file or other device.
• math: Perform basic mathematical operations like addition and multiplication.
• conditional execution: Check for certain conditions and execute the appropriate sequence of statements.
• repetition: Perform some action repeatedly, usually with some variation.

Many computer languages provide a mechanism to call functions provided by libraries. Provided the functions in a library follow the appropriate runtime conventions (eg, method of passing arguments), then these functions may be written in any other language.