SWE102 - 2 - SOFTWARE PROCESS (Process activities (Software Specification,…
SWE102 - 2 - SOFTWARE PROCESS
Software process models
The Waterfall model
Incremental Development (Agile)
Reuse-Oriented Software Engineering
Requirements elicitation and analysis
Software design and implementation
Activites of design
Stages of testing
Testing of the system as a whole. Testing of emergent properties is particularly important.
Testing with customer data to check that the system meets the customer’s needs.
Components may be functions or objects or coherent groupings of these entities.
Individual components are tested independently;
intended to show that a system conforms to its specification and meets the requirements of the system customer.
System testing involves executing the system with test cases that are derived from the specification of the real data to be processed by the system.
Testing is the most commonly used V & V activity.
Involves checking and review processes and system testing.
As requirements change through changing business circumstances, the software that supports the business must also evolve and change.
Although there has been a demarcation between development and evolution (maintenance) this is increasingly irrelevant as fewer and fewer systems are completely new.
Software is inherently flexible and can change.
Coping with changes
A prototype is an initial version of a system used to demonstrate concepts and try out design options.
Be used in
In design processes to explore options and develop a UI design;
The requirements engineering process to help with requirements elicitation and validation;
In the testing process to run back-to-back tests.
. Improved design quality.
A closer match to users’ real needs
Improved system usability.
Reduced development effort.
May involve leaving out functionality
Error checking and recovery may not be included in the prototype;
Focus on functional rather than non-functional requirements such as reliability and security
Prototype should focus on areas of the product that are not wellunderstood;
Maybe based on rapid prototyping languages or tools
Prototypes should be discarded after development as they are not a good basis for a production system:
The prototype structure is usually degraded through rapid change;
The prototype probably will not meet normal organisational quality standards.
Prototypes are normally undocumented;
It may be impossible to tune the system to meet nonfunctional requirements;
User requirements are prioritised and the highest priority requirements are included in early increments.
Once the development of an increment is started, the requirements are frozen though requirements for later increments can continue to evolve.
Rather than deliver the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functionality.
Incremental Development and Delevery
Normal approach used in agile methods;
Evaluation done by user/customer proxy.
Develop the system in increments and evaluate each increment before proceeding to the development of the next increment;
Early increments act as a prototype to help elicit requirements for later increments.
Lower risk of overall project failure.
Customer value can be delivered with each increment so system functionality is available earlier.
The highest priority system services tend to receive the most testing.
Deploy an increment for use by end-users;
More realistic evaluation about practical use of software;
Difficult to implement for replacement systems as increments have less functionality than the system being replaced.
Most systems require a set of basic facilities that are used by different parts of the system.
As requirements are not defined in detail until an increment is to be implemented, it can be hard to identify common facilities that are needed by all increments.
The essence of iterative processes is that the specification is developed in conjunction with the software.
However, this conflicts with the procurement model of many organizations, where the complete system specification is part of the system development contract.
Boehm's Spiral Model
Each loop in the spiral represents a phase in the process.
No fixed phases such as specification or design - loops in the spiral are chosen depending on what is required.
Process is represented as a spiral rather than as a sequence of activities with backtracking.
Risks are explicitly assessed and resolved throughout the process.
Risk assessment and reduction
Risks are assessed and activities put in place to reduce the key risks.
Development and validation
A development model for the system is chosen which can be any of the generic models.
Specific objectives for the phase are identified.
The project is reviewed and the next phase of the spiral is planned.
Spiral model has been very influential in helping people think about iteration in software processes and introducing the risk-driven approach to development.
In practice, however, the model is rarely used as published for practical software development.
Change is inevitable in all large software projects.
New technologies open up new possibilities for improving implementations
Changing platforms require application changes
Business changes lead to new and changed system requirements
Change leads to rework so the costs of change include both rework (e.g. re-analysing requirements) as well as the costs of implementing new functionality
where the software process includes activities that can anticipate possible changes before significant rework is required.
where the process is designed so that changes can be accommodated at relatively low cost.
This normally involves some form of incremental development.
Proposed changes may be implemented in increments that have not yet been developed. If this is impossible, then only a single increment (a small part of the system) may have be altered to incorporate the change.
The Rational Unified Process
Brings together aspects of the 3 generic process models discussed previously.
Normally described from 3 perspectives
A static perspective that shows process activities;
A practice perspective that suggests good practice.
A dynamic perspective that shows phases over time;
A modern generic process derived from the work on the UML and associated process.
Develop an understanding of the problem domain and the system architecture.
System design, programming and testing.
Establish the business case for the system.
Deploy the system in its operating environment.
As shown by the loop in the RUP model, the whole set of phases may be enacted incrementally.
Each phase is iterative with results developed incrementally.