• Reliability: An attribute of resiliency and structural solidity. Reliability measures the level of risk and the likelihood of potential application failures. It also measures the defects injected due to modifications made to the software (its “stability” as termed by ISO). The goal for checking and monitoring Reliability is to reduce and prevent application downtime, application outages and errors that directly affect users, and enhance the image of IT and its impact on a company’s business performance.
• Efficiency
  Efficiency
  Efficiency in general describes the extent to which time or effort is well used for the intended task or purpose. It is often used with the specific purpose of relaying the capability of a specific application of effort to produce a specific outcome effectively with a minimum amount or quantity of...
  
  : The source code and software architecture attributes are the elements that ensure high performance once the application is in run-time mode. Efficiency is especially important for applications in high execution speed environments such as algorithmic or transactional processing where performance and scalability are paramount. An analysis of source code efficiency and scalability provides a clear picture of the latent business risks and the harm they can cause to customer satisfaction due to response-time degradation.
• Security
  Security
  Security is the degree of protection against danger, damage, loss, and crime. Security as a form of protection are structures and processes that provide or improve security as a condition. The Institute for Security and Open Methodologies in the OSSTMM 3 defines security as "a form of protection...
  
  : A measure of the likelihood of potential security breaches due to poor coding and architectural practices. This quantifies the risk of encountering critical vulnerabilities that damage the business.
• Maintainability
  Maintainability
  In engineering, maintainability is the ease with which a product can be maintained in order to:* isolate defects or their cause* correct defects or their cause* meet new requirements* make future maintenance easier, or* cope with a changed environment...
  
  : Maintainability includes the notion of adaptability, portability and transferability (from one development team to another). Measuring and monitoring maintainability is a must for mission-critical applications where change is driven by tight time-to-market schedules and where it is important for IT to remain responsive to business-driven changes. It is also essential to keep maintenance costs under control.
• Size: While not a quality attribute per se, the sizing of source code is a software characteristic that obviously impacts maintainability. Combined with the above quality characteristics, software size can be used to assess the amount of work produced and to be done by teams, as well as their productivity through correlation with time-sheet data, and other SDLC
  Software development process
  A software development process, also known as a software development life cycle , is a structure imposed on the development of a software product. Similar terms include software life cycle and software process. It is often considered a subset of systems development life cycle...
  
  -related metrics.

Alternative Approaches to Software Quality Definition

Software Quality Measurement

Introduction

• Application Architecture Practices
• Coding Practices
• Application Complexity
• Documentation
• Portability
• Technical & Functional Volume

Code-Based Analysis of Software Quality Attributes

Measuring Reliability

Measuring Efficiency

• Application Architecture Practices
• Appropriate interactions with expensive and/or remote resources
• Data access performance and data management
• Memory, network and disk space management
• Coding Practices
• Compliance with Object-Oriented and Structured Programming best practices (as appropriate)
• Compliance with SQL programming best practices

Measuring Security

• Application Architecture Practices
• Multi-layer design compliance
• Security best practices (Input Validation, SQL Injection, Cross-Site Scripting, etc. See CWE’s Top 25 http://www.sans.org/top25-programming-errors/ )
• Programming Practices (code level)
• Error & Exception handling
• Security best practices (system functions access, access control to programs)

Measuring Maintainability

Measuring Size

• There are several software technical sizing methods that have been widely described here: http://en.wikipedia.org/wiki/Software_Sizing. The most common technical sizing method is number of Lines Of Code (#LOC) per technology, number of files, functions, classes, tables, etc., from which backfiring Function Points can be computed;
• The most common for measuring functional size is Function Point Analysis (see http://en.wikipedia.org/wiki/Function_point). Function Point Analysis measures the size of the software deliverable from a user’s perspective. Function Point sizing is done based on user requirements and provides an accurate representation of both size for the developer/estimator and value (functionality to be delivered) and reflects the business functionality being delivered to the customer. The method includes the identification and weighting of user recognizable inputs, outputs and data stores. The size value is then available for use in conjunction with numerous measures to quantify and to evaluate software delivery and performance (Development Cost per Function Point; Delivered Defects per Function Point; Function Points per Staff Month..).

Identifying Critical Programming Errors

• Reliability
  • Avoid software patterns that will lead to unexpected behavior (Uninitialized variable, null pointers, etc.)
  • Methods, procedures and functions doing Insert, Update, Delete, Create Table or Select must include error management
  • Multi-thread functions should be made thread safe, for instance servlets or struts action classes must not have instance/non-final static fields
• Efficiency
  • Ensure centralization of client requests (incoming and data) to reduce network traffic
  • Avoid SQL queries that don’t use an index against large tables in a loop
• Security
  • Avoid fields in servlet classes that are not final static
  • Avoid data access without including error management
  • Check control return codes and implement error handling mechanisms
  • Ensure input validation to avoid cross-site scripting flaws or SQL injections flaws
• Maintainability
  • Deep inheritance trees and nesting should be avoided to improve comprehensibility
  • Modules should be loosely coupled (fanout, intermediaries) to avoid propagation of modifications
  • Enforce homogeneous naming conventions

See also

Further reading

• International Organization for Standardization. Software Engineering—Product Quality—Part 1: Quality Model. ISO, Geneva, Switzerland, 2001. ISO/IEC 9126-1:2001(E).
• Diomidis Spinellis. Code Quality: The Open Source Perspective. Addison Wesley, Boston, MA, 2006.
• Ho-Won Jung, Seung-Gweon Kim, and Chang-Sin Chung. Measuring software product quality: A survey of ISO/IEC 9126. IEEE Software, 21(5):10–13, September/October 2004.
• Stephen H. Kan. Metrics and Models in Software Quality Engineering. Addison-Wesley, Boston, MA, second edition, 2002.
• Omar Alshathry, Helge Janicke, "Optimizing Software Quality Assurance," compsacw, pp. 87–92, 2010 IEEE 34th Annual Computer Software and Applications Conference Workshops, 2010.
• Robert L. Glass. Building Quality Software. Prentice Hall, Upper Saddle River, NJ, 1992.
• Roland Petrasch, "The Definition of‚ Software Quality’: A Practical Approach", ISSRE, 1999

External links

• Linux: Fewer Bugs Than Rivals Wired Magazine, 2004