Credits

Slides adapted from the slides for the book "Software Engineering: The Current Practice" by Václav Rajlich © 2012 by Václav Rajlich

Scenarios: First Day of New Job

• Brand new company, brand new software
• Existing software replaced by brand-new software
• Existing software requires new features
• Existing software has bugs

Waterfall and Lifecycle

Lifecycle vs. Lifespan

• lifecyle
• Common terminology
• Misleading: There really isn't much of a cycle shown
• lifespan
• Better terminology
• Less commonly used

Software Lifespan Models

• Stages that software goes through from conception to death
• Software in different stages is very different to work on and requires different types of management
• Software is a product; therefore, stages are similar to the stages in the lifespan of other products

Software Lifespan & Product Stages

• Software as a product: Sales follow a curve through the lifespan
• Proprietary software: Value follows the same curve
• Names of stages are different from product stages

Staged Model

Stage 1: Initial Development

Software Lifespan
1. Initial Development
2. Evolution
3. Servicing
4. Phaseout
5. Close Down

• Similar to Waterfall, but of limited duration
• Requirements
• Design
• Implementation
• Fundamental decisions:
• technologies - programming language, coding conventions, libraries, APIs, …
• architecture - components, interactions, web-based, RESTful cloud service, desktop application
• program domain knowledge - will be needed for evolution

Stage 2: Evolution

Software Lifespan
1. Initial Development
2. Evolution
3. Servicing
4. Phaseout
5. Close Down

• Adapt the application to the ever-changing user and operating environment
• Add new features
• Correct mistakes and misunderstandings
• Respond to knowledge gained (learning) by developers and users
• Program typically grows in size and functionality
• Evolution is possible due to software architecture and knowledge of the software team

Symptom: Code Decay

• Loss of software coherence
• Loss of software knowledge
• Less coherent software requires more extensive knowledge
• If knowledge is lost, changes lead to faster deterioration
• Loss of key personnel → loss of knowledge
• Challenge: eliminate or slow code decay

Stage 3: Servicing

Software Lifespan
1. Initial Development
2. Evolution
3. Servicing
4. Phaseout
5. Close Down

• Program no longer evolves - it decays, stabilizes, or management decision not to support evolution
• Changes are limited to patches and wrappers - low cost but cause further deterioration
• Very different process from Evolution
• No need for senior engineers
• Process is stable and is easily measured and managed

Possible Solution: Reengineering

• Reversal from the 3. Servicing Stage to the 2. Evolution Stage
• Very expensive and rare
• Not simply a technical problem, as it must also address the historical knowledge of the software team

Stage 4: Phaseout

Software Lifespan
1. Initial Development
2. Evolution
3. Servicing
4. Phaseout
5. Close Down

• No more servicing
• System may still be in production
• Users must work around deficiencies

Stage 5: Close Down

Software Lifespan
1. Initial Development
2. Evolution
3. Servicing
4. Phaseout
5. Close Down

• Software is disconnected from users
• Users are directed to a replacement
• "Exit Strategy" is needed
• Changing to another system requires training
• What to do with all the data?

Software Lifespan

1. Initial Development
2. Evolution
3. Servicing
4. Phaseout
5. Close Down

Perspectives

• Time
• Money
• Careers