Introduction: Software engineering goes through a series of passages that account for their inception, initial development, productive operation, upkeep, and retirement from one generation to another. This article categorizes and examines a number of methods for describing or modelling how software systems are developed. It begins with background and definitions of traditional software life cycle models that dominate most textbook discussions and current software development practices. This is followed by a more comprehensive review of the alternative models of software evolution that are of current use as the basis for organizing software engineering projects and technologies. Background: These classic software life cycle models usually include some version or subset of the following activities: System Planning: New feasible systems replace or supplement existing information processing mechanisms whether they were previously automated, manual. Requirement Analysis: Identifies the problems a new software system is suppose to solve, its operational capabilities, its desired performance characteristics, and the resource infrastructure needed to support system operation and maintenance. Prototyping: Identifies and potentially formalizes the objects of computation, their attributes and relationships, the operations that transform these objects, the constraints that restrict system behavior, and so forth. Architectural Design: Defines the interconnection and resource interfaces between system subsystems, components, and modules in ways suitable for their detailed design and overall configuration management. Component Implementation and Debugging: Codifies the preceding specifications into operational source code implementations and validates their basic operation. Software Integration and Testing: Affirms and sustains the overall integrity of the software system architectural configuration through verifying the consistency and completeness of implemented modules, verifying the resource interfaces and interconnections against their specifications, and validating the performance of the system and subsystems against their requirements. Documentation and Delivery: packaging and rationalizing recorded system development descriptions into systematic documents and user guides, all in a form suitable for dissemination and system support. Deployment and Installation: providing directions for installing the delivered software into the local computing environment, configuring operating systems parameters and user access privileges, and running diagnostic test cases to assure the viability of basic system operation. Software Maintenance: sustaining the useful operation of a system in its target environment by providing requested functional enhancements, repairs, performance.

Introduction Software systems come and go through a series of passages that account for their inception, initial development, productive operation, upkeep, and retirement from one generation to another. This article categorizes and examines a number of methods for describing or modeling how software systems are developed. It begins with background and definitions of traditional software life cycle models that dominate most textbook discussions and current software development practices. This is followed by a more comprehensive review of the alternative models of software evolution that are of current use as the basis for organizing software engineering projects and technologies.