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SWE102 - 2 - SOFTWARE PROCESS (Process activities (Software Specification,…
SWE102 - 2 - SOFTWARE PROCESS
Software process models
Common Software Process Models
Incremental Development
(Agile or Plan-Driven)
Scrum
XP - Extreme Programming
Reuse-Oriented Software Engineering
(Agile or Plan-Deriven)
Stages
Requirements Modification
System Design With Reuse
Development and Integration
Components Analysis
Requirements Specification
The Waterfall model
(Plan Driven)
Categorize
Agile
Planning is increamental and it is easier to change the process to reflect changing customer requirements
Plan-Driven
All activities are planned in advance and progress measures against this project
Process activities
Software Specification
Requirements elicitation and analysis
Requirements specification
Feasibility study
Requirements validation
Software design and implementation
Design
Activites of design
Interface Design
where you define the interfaces
between system components.
Component Design
where you take each system
component and design how it will operate.
Database Design
where you design the system data structures and how these are to be represented in a database.
Architecture 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.
Output
Interface Specification
Component Specification
Database Specification
Architecture Specification
Input
Requirement specification
Data description
Platform information
Implementation
Programming
Write code
Test code
Software Validation
Stages of testing
System Testing
Testing of the system as a whole. Testing of emergent properties is particularly important.
Acceptance Testing
Testing with customer data to check that the system meets the customer’s needs.
Component testing
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.
Activies
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.
Software Evolution
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
Two ways of coping with changes
Incremental Delivery
Introduction
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
Increamental Development
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;
Increamental Delevery
Introduce
Difficult to implement for replacement systems as increments have less functionality than the system being replaced.
Deploy an increment for use by end-users;
More realistic evaluation about practical use of software;
Advantages
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.
Problems
1
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.
2
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.
Prototyping
Introduce
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.
Benefits
. Improved design quality.
A closer match to users’ real needs
Improved system usability.
Improved maintainability.
Reduced development effort.
Prototyping Development
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 well understood;
Maybe based on rapid prototyping languages or tools
The Process
Define Prototype Fucntionality
Outline Definition
Develop Prototype
Excutable Prototype
Establish Prototype Objectives
Prototyping Plan
Evaluate Prototype
Evaluate Report
Throw-Away Prototyping
Prototypes should be discarded after development as they are not a good basis for a production system:
Reasons
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;
Boehm's Spiral Model
Introduce
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.
Sectors
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.
Objective setting
Specific objectives for the phase are identified.
Planning
The project is reviewed and the next phase of the spiral is planned.
Usage
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.
Introduction
Issues
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
Approaches
Change Avoidance
( Prototype )
where the software process includes activities that can anticipate possible changes before significant rework is required.
Change Tolerance
( Incremental Delivery )
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
Introduce
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.
Phases
Elaboration
Develop an understanding of the problem domain and the system architecture.
Construction
System design, programming and testing.
Inception
Establish the business case for the system.
Transition
Deploy the system in its operating environment.
Iteration
Cross-phase iteration
As shown by the loop in the RUP model, the whole set of phases may be enacted incrementally.
In-phase iteration
Each phase is iterative with results developed incrementally.
Software Process
Definition
A software process is a set of related activities that leads to the production of a software
product.
Four fundmental
activities
Design and Implementation
Software Validation
Software Requirement
Software evolution
Includes
Four fundamental activities
Others
Products
Roles
Pre- and Post-condition