Software Reliability Measurement Techniques

Reliability metrics are used to quantitatively expressed the reliability of the software product. The option of which parameter is to be used depends upon the type of system to which it applies & the requirements of the application domain.

Measuring software reliability is a severe problem because we don't have a good understanding of the nature of software. It is difficult to find a suitable method to measure software reliability and most of the aspects connected to software reliability. Even the software estimates have no uniform definition. If we cannot measure the reliability directly, something can be measured that reflects the features related to reliability.

The current methods of software reliability measurement can be divided into four categories:

1. Product Metrics

Product metrics are those which are used to build the artifacts, i.e., requirement specification documents, system design documents, etc. These metrics help in the assessment if the product is right sufficient through records on attributes like usability, reliability, maintainability & portability. In these measurements are taken from the actual body of the source code.

1. Software size is thought to be reflective of complexity, development effort, and reliability. Lines of Code (LOC), or LOC in thousands (KLOC), is an initial intuitive approach to measuring software size. The basis of LOC is that program length can be used as a predictor of program characteristics such as effort &ease of maintenance. It is a measure of the functional complexity of the program and is independent of the programming language.
2. Function point metric is a technique to measure the functionality of proposed software development based on the count of inputs, outputs, master files, inquires, and interfaces.
3. Test coverage metric size fault and reliability by performing tests on software products, assuming that software reliability is a function of the portion of software that is successfully verified or tested.
4. Complexity is directly linked to software reliability, so representing complexity is essential. Complexity-oriented metrics is a way of determining the complexity of a program's control structure by simplifying the code into a graphical representation. The representative metric is McCabe's Complexity Metric.
5. Quality metrics measure the quality at various steps of software product development. An vital quality metric is Defect Removal Efficiency (DRE). DRE provides a measure of quality because of different quality assurance and control activities applied throughout the development process.

2. Project Management Metrics

Project metrics define project characteristics and execution. If there is proper management of the project by the programmer, then this helps us to achieve better products. A relationship exists between the development process and the ability to complete projects on time and within the desired quality objectives. Cost increase when developers use inadequate methods. Higher reliability can be achieved by using a better development process, risk management process, configuration management process.

These metrics are:

• Number of software developers
• Staffing pattern over the life-cycle of the software
• Cost and schedule
• Productivity

3. Process Metrics

Process metrics quantify useful attributes of the software development process & its environment. They tell if the process is functioning optimally as they report on characteristics like cycle time & rework time. The goal of process metric is to do the right job on the first time through the process. The quality of the product is a direct function of the process. So process metrics can be used to estimate, monitor, and improve the reliability and quality of software. Process metrics describe the effectiveness and quality of the processes that produce the software product.

Examples are:

• The effort required in the process
• Time to produce the product
• Effectiveness of defect removal during development
• Number of defects found during testing
• Maturity of the process

4. Fault and Failure Metrics

A fault is a defect in a program which appears when the programmer makes an error and causes failure when executed under particular conditions. These metrics are used to determine the failure-free execution software.

To achieve this objective, a number of faults found during testing and the failures or other problems which are reported by the user after delivery are collected, summarized, and analyzed. Failure metrics are based upon customer information regarding faults found after release of the software. The failure data collected is therefore used to calculate failure density, Mean Time between Failures (MTBF), or other parameters to measure or predict software reliability.