Lecture 1 (Part III)

Question 1

Describe the Waterfall Model

Answer 1

1. Analysis: Requirement Engineering Process
   
   • Feasibility: check if financially/technically feasible
   • Requirement analysis: understanding the customers requirements and its specifications
   • Requirement specification: describing the requirement specifications in detail
   • Requirement validity: are they valid?
2. Design:
   
   • design a solution for the requirements and specifications
   • translate the requirements into a solution that meets the specifications
   • develop a software to meet the customers requirements.
3. Implementation & Unit Testing:
   
   • translate the solution into a executable program/code
   • interleaving with design
4. Integration, System Testing and Deployment:
   
   • verification & validity: to check if it meets the requirements
   • testing is done through different test cases. Most common in V&V (above)
5. Maintenance and Evolution: Maintaining the software and adding functionality
   
   • fixing errors, bugs
   • improve existing functionality
   • adding new functionality if needed

Each step has to be completed before the next step.

Question 2

What are the Advantages & Disadvantages of the waterfall model?

Answer 2

Advantages:
- Usable where there are stable requirements
- can be applied in very large projects where work is being done on multiple sites at the same time
- easy to measure progress

Disadvantages:
- Not good with changing requirements
- Not flexible

Question 3

Where can Waterfall models be used?

Answer 3

Due to its advantages and limitations, the waterfall model can only be used in development of three types of softwares:

• Embedded systems: systems where software has to interface with hardware
• Critical systems: where there is extensive requirement for safety and security analysis.
• Large Software Systems: Systems that are developed by multiple different partner companies and are part of broader systems.

Question 4

What is ‘Incremental Development’ ?

Answer 4

Development method that uses both plan-driven and agile methodologies. Better suited for systems which has changing requirements or a possibility of that

• Development in increments
• Evaluate after each step before moving to the next step.
• Evaluation done by user

Question 5

How are requirements handled in Incremental Development?

Answer 5

• Requirements are prioritised
• Higher priority requirements are handled in earlier increments
• Requirements are frozen during development
• Requirements for other increments can evolve later.

Question 6

What is ‘Incremental Delivery’ ?

Answer 6

• Deploy increments for use by end-users
• More realistic feedback on the increments which can be used for development
• Hard for replacement systems as the increment has less functionality than the system it is replacing.

Question 7

What are the Advantages & Limitations of Incremental Development?

Answer 7

Advantages:
- Customer value provided with each increment
- Less chance of total project failure
- High priority requirement is tested the most
- Functionality is provided earlier
- Earlier increments are seen as prototypes to elicit requirements for later increments.

Disadvantages:
- process not visible
- structure/architecture is degraded when new increments are added
- specification is not known until increment is implemented, so it’s hard to identify common functionalities amongst different increments
- specification is developed with software, this conflicts with procurement of companies, since they define by contract.

Question 8

What are the properties of a ‘Boehm’s Spiral Model’ ?

Answer 8

• Loop represents phases in the process
• Risk is assessed and resolved throughout the process
• Flexible Loops/Phases i.e no fixed loops/phases. They are chosen depending on what is required.

Question 9

What are the different sectors of ‘Boehm’s Spiral Model’? Where is it used?

Answer 9

**Acronym: DROP
- Development & Validation: A development method is chosen for the system

• Risk assessment & reduction: Risk is assessed and activities are put in place to reduce them
• Objective setting: specific objectives for phases are identified
• Planning: project is reviewed and the next phase is planned.

Used in:
- Introduced iteration in software process
- Introduced risk-driven approach to development

however rarely used

Question 10

What is ‘Reuse Oriented SE’ ?

Answer 10

• Systematic usage of existing software
• Systems are integrated from existing components or COTS (Commercial-of-the-shelf) systems
• Now it is the standard method for developing various business systems

Question 11

What is the ‘process’ of Reuse Oriented SE? Give examples

Answer 11

**Acronym: CSRD
- Component Analysis
- System design using reuse
- Requirements modification/adaptation
- Development & Integration

Examples:
- Web services developed according to standards and capable of remote invocation

• Collection of objects developed as a package to be integrated with a component framework

Stand-alone software systems (COTS) for usage in specific environments