To improve software reliability can be applied at different stages of a program’s development, in the case of real software. These stages principally include: requirements, design, programming, testing, and runtime evaluation. The study of theoretical software reliability is predominantly concerned with the concept of correctness, a mathematical field of computer science which is an outgrowth of language and automata theory.

Requirements

A program cannot be expected to work as desired if the developers of the program do not, in fact, know the program’s desired behaviour in advance, or if they cannot at least determine its desired behaviour in parallel with development, in sufficient detail. What level of detail is considered sufficient is hotly debated. The idea of perfect detail is attractive, but may be impractical, if not actually impossible, in practice. This is because the desired behaviour tends to change as the possible range of the behaviour is determined through actual attempts, or more accurately, failed attempts, to achieve it.

Whether a program’s desired behaviour can be successfully specified in advance is a moot point if the behaviour cannot be specified at all, and this is the focus of attempts to formalize the process of creating requirements for new software projects. In situ with the formalization effort is an attempt to help inform non-specialists, particularly non-programmers, who commission software projects without sufficient knowledge of what computer software is in fact capable. Communicating this knowledge is made more difficult by the fact that, as hinted above, even programmers cannot always know in advance what is actually possible for software in advance of trying.

Design

While requirements are meant to specify what a program should do, design is meant, at least at a high level, to specify how the program should do it. The usefulness of design is also questioned by some, but those who look to formalize the process of ensuring reliability often offer good software design processes as the most significant means to accomplish it. Software design usually involves the use of more abstract and general means of specifying the parts of the software and what they do. As such, it can be seen as a way to break a large program down into many smaller programs, such that those smaller pieces together do the work of the whole program.

The purposes of high-level design are as follows. It separates what are considered to be problems of architecture, or overall program concept and structure, from problems of actual coding, which solve problems of actual data processing. It applies additional constraints to the development process by narrowing the scope of the smaller software components, and thereby — it is hoped — removing variables which could increase the likelihood of programming errors. It provides a program template, including the specification of interfaces, which can be shared by different teams of developers working on disparate parts, such that they can know in advance how each of their contributions will interface with those of the other teams. Finally, and perhaps most controversially, it specifies the program independently of the implementation language or languages, thereby removing language-specific biases and limitations which would otherwise creep into the design, perhaps unwittingly on the part of programmer-designers.

Programming

The history of computer programming language development can often be best understood in the light of attempts to master the complexity of computer programs, which otherwise becomes more difficult to understand in proportion (perhaps exponentially) to the size of the programs. (Another way of looking at the evolution of programming languages is simply as a way of getting the computer to do more and more of the work, but this may be a different way of saying the same thing.) Lack of understanding of a program’s overall structure and functionality is a sure way to fail to detect errors in the program, and thus the use of better languages should, conversely, reduce the number of errors by enabling a better understanding.

Improvements in languages tend to provide incrementally what software design has attempted to do in one fell swoop: consider the software at ever greater levels of abstraction. Such inventions as statement, sub-routine, file, class, template, library, component and more have allowed the arrangement of a program’s parts to be specified using abstractions such as layers, hierarchies and modules, which provide structure at different granularities, so that from any point of view the program’s code can be imagined to be orderly and comprehensible.

In addition, improvements in languages have enabled more exact control over the shape and use of data elements, culminating in the abstract data type. These data types can be specified to a very fine degree, including how and when they are accessed, and even the state of the data before and after it is accessed..

Testing

Software testing, when done correctly, can increase overall software quality of conformance by testing that the product conforms to its requirements. Testing includes, but is not limited to:

1. Unit Testing
2. Functional Testing
3. Performance Testing
4. Failover Testing
5. Usability Testing

A number of agile methodologies use testing early in the development cycle to ensure quality in their products. For example, the test-driven development practice, where tests are written before the code they will test, is used in Extreme Programming to ensure quality.

Runtime

Runtime reliability determinations are similar to tests, but go beyond simple confirmation of behaviour to the evaluation of qualities such as performance and interoperability with other code or particular hardware configurations…..

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]]> http://sehelsoft.wordpress.com/2008/10/25/reliable-software-programming/feed/ 3 sehelsoft http://sehelsoft.wordpress.com/2008/10/10/application-software-development/ http://sehelsoft.wordpress.com/2008/10/10/application-software-development/#comments Fri, 10 Oct 2008 06:25:48 +0000 sehelsoft http://sehelsoft.wordpress.com/?p=27 ]]> Application software is a subclass of computer software that employs the capabilities of a computer directly and thoroughly to a task that the user wishes to perform. This should be contrasted with system software which is involved in integrating a computer’s various capabilities, but typically does not directly apply them in the performance of tasks that benefit the user. In this context the term application refers to both the application software and its implementation.

There are many subtypes of application software:

• Enterprise software addresses the needs of organization processes and data flow, often in a large distributed ecosystem. (Examples include Financial, Customer Relationship Management, and Supply Chain Management). Note that Departmental Software is a sub-type of Enterprise Software with a focus on smaller organizations or groups within a large organization. (Examples include Travel Expense Management, and IT Helpdesk)
• Enterprise infrastructure software provides common capabilities needed to create Enterprise Software systems. (Examples include Databases, Email servers, and Network and Security Management)
• Information worker software addresses the needs of individuals to create and manage information, often for individual projects within a department, in contrast to enterprise management. Examples include time management, resource management, documentation tools, analytical, and collaborative. Word processors, spreadsheets, email and blog clients, personal information system, and individual media editors may aid in multiple information worker tasks.
• Content access software is software used primarily to access content without editing, but may include software that allows for content editing. Such software addresses the needs of individuals and groups to consume digital entertainment and published digital content. (Examples include Media Players, Web Browsers, Help browsers, and Games)
• Educational software is related to Media and Entertainment Software, but has distinct requirements for delivering evaluations (tests) and tracking progress through material. It is also related to collaboration software in that many Educational Software systems include collaborative capabilities.
• Simulation software are computer software for simulation of physical or abstract systems for either research, training or entertainment purposes.
• Media development software addresses the needs of individuals who generate print and electronic media for others to consume, most often in a commercial or educational setting. This includes Graphic Art software, Desktop Publishing software, Multimedia Development software, HTML editors, Digital Animation editors, Digital Audio and Video composition, and many others.
• Product engineering software is used in developing hardware and software products. This includes computer aided design (CAD), computer aided engineering (CAE), computer language editing and compiling tools, Integrated Development Environments, and Application Programmer Interfaces.

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Encyclopedia

Practical computer systems divide software systems into three major classes: system software, programming software and application software, although the distinction is arbitrary, and often blurred.

• System software helps run the computer hardware and computer system. It includes operating systems, device drivers, diagnostic tools, servers, windowing systems, utilities and more. The purpose of systems software is to insulate the applications programmer as much as possible from the details of the particular computer complex being used, especially memory and other hardware features, and such accessory devices as communications, printers, readers, displays, keyboards, etc.
• Programming software usually provides tools to assist a programmer in writing computer programs and software using different programming languages in a more convenient way. The tools include text editors, compilers, interpreters, linkers, debuggers, and so on. An Integrated development environment (IDE) merges those tools into a software bundle, and a programmer may not need to type multiple commands for compiling, interpreter, debugging, tracing, and etc., because the IDE usually has an advanced graphical user interface, or GUI.
• Application software allows end users to accomplish one or more specific (non-computer related) tasks. Typical applications include industrial automation, business software, educational software, medical software, databases, and computer games. Businesses are probably the biggest users of application software, but almost every field of human activity now uses some form of application software. It is used to automate all sorts of functions.

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Today, software has grown in complexity and size. The software product developed by a developer is according to the System Requirement Specification. Every software product has a target audience.

There are many approaches to software testing, but effective testing of complex products is essentially a process of investigation, not merely a matter of creating and following routine procedure.

Software Testing Axioms

1. It is impossible to test a program completely.
2. Software testing is risk based exercise.
3. Testing can’t show that bugs dont exist.
4. The more bugs you find, the more bugs there are.
5. Not all the bugs you find will be fixed.
6. Product specifications are never final.

Levels of testing

• Unit testing tests the minimal software component, or module. Each unit (basic component) of the software is tested to verify that the detailed design for the unit has been correctly implemented. In an Object-oriented environment, this is usually at the class level, and the minimal unit tests include the constructors and destructors.
• Integration testing exposes defects in the interfaces and interaction between integrated components (modules). Progressively larger groups of tested software components corresponding to elements of the architectural design are integrated and tested until the software works as a system.
• Functional testing tests at any level (class, module, interface, or system) for proper functionality as defined in the specification.
• System testing tests a completely integrated system to verify that it meets its requirements.
• System integration testing verifies that a system is integrated to any external or third party systems defined in the system requirements.
• Acceptance testing can be conducted by the end-user, customer, or client to validate whether or not to accept the product. Acceptance testing may be performed as part of the hand-off process between any two phases of development. See also Development stage

Alpha testing is simulated or actual operational testing by potential users/customers or an independent test team at the developers’ site. Alpha testing is often employed for off-the-shelf software as a form of internal acceptance testing, before the software goes to beta testing.

Beta testing comes after alpha testing. Versions of the software, known as beta versions, are released to a limited audience outside of the company. The software is released to groups of people so that further testing can ensure the product has few faults or bugs. Sometimes, beta versions are made available to the open public to increase the feedback field to a maximal number of future users.

Not all errors or defects reported must be fixed by a software development team. Some may be caused by errors in configuring the test software to match the development or production environment. Some defects can be handled by a workaround in the production environment. Others might be deferred to future releases of the software, or the deficiency might be accepted by the business users.

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Encyclopedia

• Efficiency: it is referred to the system resource consumption (computer processor, memory, slow devices, networks and to some extent even user interaction) which must be the lowest possible.
• Reliability: the results of the program must be correct, which not only implies a correct code implementation but also reduction of error propagation (e.g. resulting from data conversion) and prevention of typical errors (overflow, underflow or zero division).
• Robustness: a program must anticipate situations of data type conflict and all other incompatibilities which result in run time errors and stop of the program. The focus of this aspect is the interaction with the user and the handling of error messages.
• Portability: it should work as it is in any software and hardware environment, or at least without relevant reprogramming.
• Readability: the purpose of the main program and of each subroutine must be clearly defined with appropriate comments and self explanatory chose of symbolic names (constants, variables, function names, classes, and methods).

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]]> http://sehelsoft.wordpress.com/2008/08/21/software-programming/feed/ 1 sehelsoft http://sehelsoft.wordpress.com/2008/08/07/software-development-process/ http://sehelsoft.wordpress.com/2008/08/07/software-development-process/#comments Thu, 07 Aug 2008 10:44:30 +0000 sehelsoft http://sehelsoft.wordpress.com/?p=17 ]]> A software development process is a structure imposed on the development of a software product. Synonyms include software life cycle and software process. There are several models for such processes, each describing approaches to a variety of tasks or activities that take place during the process. . Let us see the steps involve in any software development.

Domain Analysis

Often the first step in attempting to design a new piece of software, whether it be an addition to an existing software, a new application, a new subsystem or a whole new system, is what is generally referred to as “Domain Analysis”. Assuming that the developers (including the analysts) are not sufficiently knowledgeable in the subject area of the new software, the first task is to investigate the so-called “domain” of the software. The more knowledgeable they are about the domain already, the less the work required. Another objective of this work is to make the analysts who will later try to elicit and gather the requirements from the area experts or professionals, speak with them in the domain’s own terminology and to better understand what is being said by these people. Otherwise they will not be taken seriously. So, this phase is an important prelude to extracting and gathering the requirements.

Software Elements Analysis

The most important task in creating a software product is extracting the requirements. Clients typically know what they want, but not what software should do, while incomplete, ambiguous or contradictory requirements are recognized by skilled and experienced software engineers. Frequently demonstrating live code may help reduce the risk that the requirements are incorrect.

Specification

Specification is the task of precisely describing the software to be written, possibly in a rigorous way. In practice, most successful specifications are written to understand and fine-tune applications that were already well-developed, although safety-critical software systems are often carefully specified prior to application development. Specifications are most important for external interfaces that must remain stable.

Implementation (or coding)

Reducing a design to code may be the most obvious part of the software engineering job, but it is not necessarily the largest portion.

Testing

Testing of parts of software, especially where code by two different engineers must work together falls to the software engineer.

Documentation

An important (and often overlooked) task is documenting the internal design of software for the purpose of future maintenance and enhancement. Documentation is most important for external interfaces.

Software Training and Support

A large percentage of software projects fail because the developers fail to realize that it doesn’t matter how much time and planning a development team puts into creating software if nobody in an organization ends up using it. People are occasionally resistant to change and avoid venturing into an unfamiliar area so, as a part of the deployment phase, it is very important to have training classes for the most enthusiastic software users (build excitement and confidence), shifting the training towards the neutral users intermixed with the avid supporters, and finally incorporate the rest of the organization into adopting the new software. Users will have lots of questions and software problems which lead to the next phase of software.

Maintenance

Maintaining and enhancing software to cope with newly discovered problems or new requirements can take far more time than the initial development of the software. Not only may it be necessary to add code that does not fit the original design but just determining how software works at some point after it is completed may require significant effort by a software engineer. About ⅔ of all software engineering work is maintenance, but this statistic can be misleading. A small part of that is fixing bugs. Most maintenance is extending systems to do new things, which in many ways can be considered new work.

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Reference: Answers.com

The main financial return on open source comes from selling services, such as training and support, rather than the software itself. Many contributors to open source software (especially those developing software tools) also feel that there is a significant long-term return in the form of improved resources and capabilities within the software industry. Now there are mainly fours types of software working like:

Freeware

Freeware is copyrighted computer software which is made available for use free of charge, for an unlimited time, as opposed to shareware where the user is required to pay (e.g. after some trial period or for additional functionality). Authors of freeware often want to “give something to the community”, but also want credit for their software and to retain control of its future development. Sometimes when programmers decide to stop developing a freeware product, they will give the source code to another programmer or release the product’s source code to the public as free software.

Shareware

Shareware is a marketing method for computer software. Shareware software is typically obtained free of charge, either by downloading from the Internet or on magazine cover-disks. A user tries out the program, and thus shareware has also been known as “try before you buy”. A shareware program is accompanied by a request for payment, and the software’s distribution license often requires such a payment.

Open source

Open source describes the principles and methodologies to promote open access to the production and design process for various goods, products, resources and technical conclusions or advice. The term is most commonly applied to the source code of software that is made available to the general public with either relaxed or non-existent intellectual property restrictions. This allows users to create user-generated software content through either incremental individual effort, or collaboration.

Commercial

Commercial software is computer software sold for commercial purposes or that serves commercial purposes. Commercial software is most often proprietary software, but free software is also used as commercial software. All or parts of software packages and services that support commerce are increasingly made available as free software, including products from Red Hat, Apple Computer, Sun Microsystems, and Google.

Software Development

Reference: Wikipedia.org

• Extensibility – New capabilities can be added to the software without major changes to the underlying architecture.
• Robustness – The software is able to operate under stress or tolerate unpredictable or invalid input. For example, it can be designed with resilience to low memory conditions.
• Reliability – The software is able to perform a required function under stated conditions for a specified period of time.
• Fault-tolerance – The software is resistant to and able to recover from component failure.
• Security – The software is able to withstand hostile acts and influences.
• Maintainability – The software can be restored to a specified condition within a specified period of time. For example, virus software may include the ability to periodically receive virus definition updates in order to maintain the software’s effectiveness.
• Compatibility – The software is able to operate with other products that are designed for interoperability with another product. For example, a piece of software may be backward-compatible with an older version of itself.
• Modularity – the resulting software comprises of well defined, independent components. That leads to better maintainability. The components could be then implemented and tested in isolation before being integrated to form a desired software system. This allows division of work in a software development project.
• Reuse – the modular components designed should capture the essence of the functionality expected out of them and no more or less. This single-minded purpose render the components reusable wherever there are similar needs in other designs.

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Reference: Answers.com

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