Software Engineering

SE Process Activities

Four fundamental software engineering activities

1. Software specification

   • The functionality of the software and constraints on its operation must be defined

     

2. Software development

   • The software to meet the specification must be produced

   

3. Software Validation

   • The software must be validated to ensure that it does what the customer wants
   • Validation:
     • Are we building the right systems?
     • Conforms to customers' expectations and experience
   • Verification
     • Are we building the system right?
     • Conforms to specification
   • Techniques:
     • Testing of programs and prototypes
     • Reviewing of specifications, documentation and programs
   • Stages of testing
     • Component testing $\to$ System testing $\to$ Customer testing

4. Software evolution

   • The software must evolve to meet changing customer needs

Software Process Models

1. Waterfall Model (Plan-driven)

   • Seperate and distinct phases of specification, design, implementation, test, and operations

   

2. Incremental Model (Plan-driven, agile or mix)

   • Specification, development and validation are interleaved.
   • System is developed as a series of versions (increments), with each version adding functionality to the previous version.

   

3. Integration & configurations model (Reuse)

   • System is assembled from existing configurable components.
   • Plan-driven or agile

   

Waterfall

It is a plan-driven process, as the process activities are planned and scheduled before starting development.

1. Requirements analysis and definition
   • The system’s services, constraints and goals are established by consultation with system users. They are then defined in detail and serve as a system specification.
2. System and software design
   • The systems design process allocates the requirements to either hardware or software systems. It establishes an overall system architecture. Software design involves identifying and describing the fundamental software system abstractions and their relationships.
3. Implementation and unit testing
   • During this stage, the software design is realized as a set of programs or program units. Unit testing involves verifying that each unit meets its specification.
4. Integration and system testing
   • The individual program units or programs are integrated and tested as a complete system to ensure that the software requirements have been met. After testing, the software system is delivered to the customer.
5. Operation and maintenance
   • Normally, this is the longest life-cycle phase. The system is installed and put into practical use. Maintenance involves correcting errors that were not discovered in earlier stages of the life cycle, improving the implementation of system units, and enhancing the system’s services as new requirements are discovered.

When should you consider waterfall?

1. Embedded systems Because of the inflexibility of hardware it is usually not possibly to delay decisions on the software’s functionality until it is being implemented.
2. Life critical systems Because the specification and design documents must be complete so that it is possible to create an extensive security analysis of the software specification and design. Safety-related problems in the specs and design are usually very expensive to correct at the implementation stage.
3. Large software systems that are a part of broader engineering systems Because the hardware in the system may be developed using a similar model and companies find it easier to use a common model for hardware and software. Furthermore, where several companies are involved, complete specs may be needed to allow for the independent development of different subsystems.

How can I decide if agile or waterfall is best fit for my situation?

Boehm: Analyse af home ground

The waterfall model should not be used in developing systems where informal team communication is possible and software requirements change quickly. In this case, iterative and agile methods are better.

---

Last update: January 22, 2020