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