Software Processes

Содержание

Слайд 2

Topics covered Software process models Process activities Coping with change Process

Topics covered

Software process models
Process activities
Coping with change
Process improvement

Chapter 2 Software Processes

30/10/2014

Слайд 3

The software process A structured set of activities required to develop

The software process

A structured set of activities required to develop a

software system.
Many different software processes but all involve:
Specification – defining what the system should do;
Design and implementation – defining the organization of the system and implementing the system;
Validation – checking that it does what the customer wants;
Evolution – changing the system in response to changing customer needs.
A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective.

Chapter 2 Software Processes

30/10/2014

Слайд 4

Software process descriptions When we describe and discuss processes, we usually

Software process descriptions

When we describe and discuss processes, we usually talk

about the activities in these processes such as specifying a data model, designing a user interface, etc. and the ordering of these activities.
Process descriptions may also include:
Products, which are the outcomes of a process activity;
Roles, which reflect the responsibilities of the people involved in the process;
Pre- and post-conditions, which are statements that are true before and after a process activity has been enacted or a product produced.

Chapter 2 Software Processes

30/10/2014

Слайд 5

Plan-driven and agile processes Plan-driven processes are processes where all of

Plan-driven and agile processes

Plan-driven processes are processes where all of the

process activities are planned in advance and progress is measured against this plan.
In agile processes, planning is incremental and it is easier to change the process to reflect changing customer requirements.
In practice, most practical processes include elements of both plan-driven and agile approaches.
There are no right or wrong software processes.

Chapter 2 Software Processes

30/10/2014

Слайд 6

Software process models Chapter 2 Software Processes 30/10/2014

Software process models

Chapter 2 Software Processes

30/10/2014

Слайд 7

Software process models The waterfall model Plan-driven model. Separate and distinct

Software process models

The waterfall model
Plan-driven model. Separate and distinct phases of

specification and development.
Incremental development
Specification, development and validation are interleaved. May be plan-driven or agile.
Integration and configuration
The system is assembled from existing configurable components. May be plan-driven or agile.
In practice, most large systems are developed using a process that incorporates elements from all of these models.

Chapter 2 Software Processes

30/10/2014

Слайд 8

The waterfall model Chapter 2 Software Processes 30/10/2014

The waterfall model

Chapter 2 Software Processes

30/10/2014

Слайд 9

Waterfall model phases There are separate identified phases in the waterfall

Waterfall model phases

There are separate identified phases in the waterfall model:
Requirements

analysis and definition
System and software design
Implementation and unit testing
Integration and system testing
Operation and maintenance
The main drawback of the waterfall model is the difficulty of accommodating change after the process is underway. In principle, a phase has to be complete before moving onto the next phase.

Chapter 2 Software Processes

30/10/2014

Слайд 10

Waterfall model problems Inflexible partitioning of the project into distinct stages

Waterfall model problems

Inflexible partitioning of the project into distinct stages makes

it difficult to respond to changing customer requirements.
Therefore, this model is only appropriate when the requirements are well-understood and changes will be fairly limited during the design process.
Few business systems have stable requirements.
The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites.
In those circumstances, the plan-driven nature of the waterfall model helps coordinate the work.

Chapter 2 Software Processes

30/10/2014

Слайд 11

Incremental development Chapter 2 Software Processes 30/10/2014

Incremental development

Chapter 2 Software Processes

30/10/2014

Слайд 12

Incremental development benefits The cost of accommodating changing customer requirements is

Incremental development benefits

The cost of accommodating changing customer requirements is reduced.


The amount of analysis and documentation that has to be redone is much less than is required with the waterfall model.
It is easier to get customer feedback on the development work that has been done.
Customers can comment on demonstrations of the software and see how much has been implemented.
More rapid delivery and deployment of useful software to the customer is possible.
Customers are able to use and gain value from the software earlier than is possible with a waterfall process.

Chapter 2 Software Processes

30/10/2014

Слайд 13

Incremental development problems The process is not visible. Managers need regular

Incremental development problems

The process is not visible.
Managers need regular deliverables

to measure progress. If systems are developed quickly, it is not cost-effective to produce documents that reflect every version of the system.
System structure tends to degrade as new increments are added.
Unless time and money is spent on refactoring to improve the software, regular change tends to corrupt its structure. Incorporating further software changes becomes increasingly difficult and costly.

Chapter 2 Software Processes

30/10/2014

Слайд 14

Integration and configuration Based on software reuse where systems are integrated

Integration and configuration

Based on software reuse where systems are integrated from

existing components or application systems (sometimes called COTS -Commercial-off-the-shelf) systems).
Reused elements may be configured to adapt their behaviour and functionality to a user’s requirements
Reuse is now the standard approach for building many types of business system
Reuse covered in more depth in Chapter 15.

Chapter 2 Software Processes

30/10/2014

Слайд 15

Types of reusable software Stand-alone application systems (sometimes called COTS) that

Types of reusable software

Stand-alone application systems (sometimes called COTS) that are

configured for use in a particular environment.
Collections of objects that are developed as a package to be integrated with a component framework such as .NET or J2EE.
Web services that are developed according to service standards and which are available for remote invocation.

Chapter 2 Software Processes

30/10/2014

Слайд 16

Reuse-oriented software engineering Chapter 2 Software Processes 30/10/2014

Reuse-oriented software engineering

Chapter 2 Software Processes

30/10/2014

Слайд 17

Key process stages Requirements specification Software discovery and evaluation Requirements refinement

Key process stages

Requirements specification
Software discovery and evaluation
Requirements refinement
Application system configuration
Component adaptation

and integration

Chapter 2 Software Processes

30/10/2014

Слайд 18

Advantages and disadvantages Reduced costs and risks as less software is

Advantages and disadvantages

Reduced costs and risks as less software is developed

from scratch
Faster delivery and deployment of system
But requirements compromises are inevitable so system may not meet real needs of users
Loss of control over evolution of reused system elements

Chapter 2 Software Processes

30/10/2014

Слайд 19

Process activities Chapter 2 Software Processes 30/10/2014

Process activities

Chapter 2 Software Processes

30/10/2014

Слайд 20

Process activities Real software processes are inter-leaved sequences of technical, collaborative

Process activities

Real software processes are inter-leaved sequences of technical, collaborative and

managerial activities with the overall goal of specifying, designing, implementing and testing a software system.
The four basic process activities of specification, development, validation and evolution are organized differently in different development processes.
For example, in the waterfall model, they are organized in sequence, whereas in incremental development they are interleaved.

Chapter 2 Software Processes

30/10/2014

Слайд 21

The requirements engineering process Chapter 2 Software Processes 30/10/2014

The requirements engineering process

Chapter 2 Software Processes

30/10/2014

Слайд 22

Software specification The process of establishing what services are required and

Software specification

The process of establishing what services are required and the

constraints on the system’s operation and development.
Requirements engineering process
Requirements elicitation and analysis
What do the system stakeholders require or expect from the system?
Requirements specification
Defining the requirements in detail
Requirements validation
Checking the validity of the requirements

Chapter 2 Software Processes

30/10/2014

Слайд 23

Software design and implementation The process of converting the system specification

Software design and implementation

The process of converting the system specification into

an executable system.
Software design
Design a software structure that realises the specification;
Implementation
Translate this structure into an executable program;
The activities of design and implementation are closely related and may be inter-leaved.

Chapter 2 Software Processes

30/10/2014

Слайд 24

A general model of the design process Chapter 2 Software Processes 30/10/2014

A general model of the design process

Chapter 2 Software Processes

30/10/2014

Слайд 25

Design activities Architectural design, where you identify the overall structure of

Design activities

Architectural design, where you identify the overall structure of the

system, the principal components (subsystems or modules), their relationships and how they are distributed.
Database design, where you design the system data structures and how these are to be represented in a database.
Interface design, where you define the interfaces between system components.
Component selection and design, where you search for reusable components. If unavailable, you design how it will operate.

Chapter 2 Software Processes

30/10/2014

Слайд 26

System implementation The software is implemented either by developing a program

System implementation

The software is implemented either by developing a program or

programs or by configuring an application system.
Design and implementation are interleaved activities for most types of software system.
Programming is an individual activity with no standard process.
Debugging is the activity of finding program faults and correcting these faults.

Chapter 2 Software Processes

30/10/2014

Слайд 27

Software validation Verification and validation (V & V) is intended to

Software validation

Verification and validation (V & V) is intended to show

that a system conforms to its specification and meets the requirements of the system customer.
Involves checking and review processes and system testing.
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.

Chapter 2 Software Processes

30/10/2014

Слайд 28

Stages of testing Chapter 2 Software Processes 30/10/2014

Stages of testing

Chapter 2 Software Processes

30/10/2014

Слайд 29

Testing stages Component testing Individual components are tested independently; Components may

Testing stages

Component testing
Individual components are tested independently;
Components may be functions

or objects or coherent groupings of these entities.
System testing
Testing of the system as a whole. Testing of emergent properties is particularly important.
Customer testing
Testing with customer data to check that the system meets the customer’s needs.

Chapter 2 Software Processes

30/10/2014

Слайд 30

Testing phases in a plan-driven software process (V-model) Chapter 2 Software Processes 30/10/2014

Testing phases in a plan-driven software process (V-model)

Chapter 2 Software Processes

30/10/2014

Слайд 31

Software evolution Software is inherently flexible and can change. As requirements

Software evolution

Software is inherently flexible and can change.
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.

Chapter 2 Software Processes

30/10/2014

Слайд 32

System evolution Chapter 2 Software Processes 30/10/2014

System evolution

Chapter 2 Software Processes

30/10/2014

Слайд 33

Coping with change Chapter 2 Software Processes 30/10/2014

Coping with change

Chapter 2 Software Processes

30/10/2014

Слайд 34

Coping with change Change is inevitable in all large software projects.

Coping with change

Change is inevitable in all large software projects.
Business changes

lead to new and changed system requirements
New technologies open up new possibilities for improving implementations
Changing platforms require application changes
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

Chapter 2 Software Processes

30/10/2014

Слайд 35

Reducing the costs of rework Change anticipation, where the software process

Reducing the costs of rework

Change anticipation, where the software process includes

activities that can anticipate possible changes before significant rework is required.
For example, a prototype system may be developed to show some key features of the system to customers.
Change tolerance, 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.

Chapter 2 Software Processes

30/10/2014

Слайд 36

Coping with changing requirements System prototyping, where a version of the

Coping with changing requirements

System prototyping, where a version of the system

or part of the system is developed quickly to check the customer’s requirements and the feasibility of design decisions. This approach supports change anticipation.
Incremental delivery, where system increments are delivered to the customer for comment and experimentation. This supports both change avoidance and change tolerance.

Chapter 2 Software Processes

30/10/2014

Слайд 37

Software prototyping A prototype is an initial version of a system

Software prototyping

A prototype is an initial version of a system used

to demonstrate concepts and try out design options.
A prototype can be used in:
The requirements engineering process to help with requirements elicitation and validation;
In design processes to explore options and develop a UI design;
In the testing process to run back-to-back tests.

Chapter 2 Software Processes

30/10/2014

Слайд 38

Benefits of prototyping Improved system usability. A closer match to users’

Benefits of prototyping

Improved system usability.
A closer match to users’ real needs.
Improved

design quality.
Improved maintainability.
Reduced development effort.

Chapter 2 Software Processes

30/10/2014

Слайд 39

The process of prototype development Chapter 2 Software Processes 30/10/2014

The process of prototype development

Chapter 2 Software Processes

30/10/2014

Слайд 40

Prototype development May be based on rapid prototyping languages or tools

Prototype development

May be 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;
Error checking and recovery may not be included in the prototype;
Focus on functional rather than non-functional requirements such as reliability and security

Chapter 2 Software Processes

30/10/2014

Слайд 41

Throw-away prototypes Prototypes should be discarded after development as they are

Throw-away prototypes

Prototypes should be discarded after development as they are not

a good basis for a production system:
It may be impossible to tune the system to meet non-functional requirements;
Prototypes are normally undocumented;
The prototype structure is usually degraded through rapid change;
The prototype probably will not meet normal organisational quality standards.

Chapter 2 Software Processes

30/10/2014

Слайд 42

Incremental delivery Rather than deliver the system as a single delivery,

Incremental delivery

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.
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.

Chapter 2 Software Processes

30/10/2014

Слайд 43

Incremental development and delivery Incremental development Develop the system in increments

Incremental development and delivery

Incremental development
Develop the system in increments and evaluate

each increment before proceeding to the development of the next increment;
Normal approach used in agile methods;
Evaluation done by user/customer proxy.
Incremental delivery
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.

Chapter 2 Software Processes

30/10/2014

Слайд 44

Incremental delivery Chapter 2 Software Processes 30/10/2014

Incremental delivery

Chapter 2 Software Processes

30/10/2014

Слайд 45

Incremental delivery advantages Customer value can be delivered with each increment

Incremental delivery advantages

Customer value can be delivered with each increment so

system functionality is available earlier.
Early increments act as a prototype to help elicit requirements for later increments.
Lower risk of overall project failure.
The highest priority system services tend to receive the most testing.

Chapter 2 Software Processes

30/10/2014

Слайд 46

Incremental delivery problems Most systems require a set of basic facilities

Incremental delivery problems

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.

Chapter 2 Software Processes

30/10/2014

Слайд 47

Process improvement Chapter 2 Software Processes 30/10/2014

Process improvement

Chapter 2 Software Processes

30/10/2014

Слайд 48

Process improvement Many software companies have turned to software process improvement

Process improvement

Many software companies have turned to software process improvement as

a way of enhancing the quality of their software, reducing costs or accelerating their development processes.
Process improvement means understanding existing processes and changing these processes to increase product quality and/or reduce costs and development time.

Chapter 2 Software Processes

30/10/2014

Слайд 49

Approaches to improvement The process maturity approach, which focuses on improving

Approaches to improvement

The process maturity approach, which focuses on improving process

and project management and introducing good software engineering practice.
The level of process maturity reflects the extent to which good technical and management practice has been adopted in organizational software development processes.
The agile approach, which focuses on iterative development and the reduction of overheads in the software process.
The primary characteristics of agile methods are rapid delivery of functionality and responsiveness to changing customer requirements.

Chapter 2 Software Processes

30/10/2014

Слайд 50

The process improvement cycle Chapter 2 Software Processes 30/10/2014

The process improvement cycle

Chapter 2 Software Processes

30/10/2014

Слайд 51

Process improvement activities Process measurement You measure one or more attributes

Process improvement activities

Process measurement
You measure one or more attributes of

the software process or product. These measurements forms a baseline that helps you decide if process improvements have been effective.
Process analysis
The current process is assessed, and process weaknesses and bottlenecks are identified. Process models (sometimes called process maps) that describe the process may be developed.
Process change
Process changes are proposed to address some of the identified process weaknesses. These are introduced and the cycle resumes to collect data about the effectiveness of the changes.

Chapter 2 Software Processes

30/10/2014

Слайд 52

Process measurement Wherever possible, quantitative process data should be collected However,

Process measurement

Wherever possible, quantitative process data should be collected
However, where organisations

do not have clearly defined process standards this is very difficult as you don’t know what to measure. A process may have to be defined before any measurement is possible.
Process measurements should be used to assess process improvements
But this does not mean that measurements should drive the improvements. The improvement driver should be the organizational objectives.

Chapter 2 Software Processes

30/10/2014

Слайд 53

Process metrics Time taken for process activities to be completed E.g.

Process metrics

Time taken for process activities to be completed
E.g. Calendar time

or effort to complete an activity or process.
Resources required for processes or activities
E.g. Total effort in person-days.
Number of occurrences of a particular event
E.g. Number of defects discovered.

Chapter 2 Software Processes

30/10/2014

Слайд 54

Capability maturity levels Chapter 2 Software Processes 30/10/2014

Capability maturity levels

Chapter 2 Software Processes

30/10/2014

Слайд 55

The SEI capability maturity model Initial Essentially uncontrolled Repeatable Product management

The SEI capability maturity model

Initial
Essentially uncontrolled
Repeatable
Product management procedures defined and used
Defined
Process

management procedures and strategies defined and used
Managed
Quality management strategies defined and used
Optimising
Process improvement strategies defined and used

Chapter 2 Software Processes

30/10/2014

Слайд 56

Key points Software processes are the activities involved in producing a

Key points

Software processes are the activities involved in producing a software

system. Software process models are abstract representations of these processes.
General process models describe the organization of software processes.
Examples of these general models include the ‘waterfall’ model, incremental development, and reuse-oriented development.
Requirements engineering is the process of developing a software specification.

Chapter 2 Software Processes

30/10/2014

Слайд 57

Key points Design and implementation processes are concerned with transforming a

Key points

Design and implementation processes are concerned with transforming a requirements

specification into an executable software system.
Software validation is the process of checking that the system conforms to its specification and that it meets the real needs of the users of the system.
Software evolution takes place when you change existing software systems to meet new requirements. The software must evolve to remain useful.
Processes should include activities such as prototyping and incremental delivery to cope with change.

Chapter 2 Software Processes

30/10/2014

- Предыдущая
Аргентинская кухня
Следующая -
Уральский центр спортивной медицины

Похожие презентации

Электронная коммерция в Интернете Саранцева О.Н. учитель информатики и ИКТ МОУ СОШ №1 г. Спасска Пензенской области
Введение в базы данных
1 Ноябрь, 2014
Разработка программного обеспечения для подключения к базам данных на платформе Microsoft .NET
Android development
Создание запросов
Офисные компьютерные технологии
Системы информационной безопасности
Презентация "Использование ИКТ как один из способов активизации познавательной деятельности школьников" - скачать презентац
Тема 3. Проекты Access
Программное обеспечение систем управления (ПО СУ)
Муниципальное общеобразовательное учреждение гимназия №1 Учитель информатики: Скабёлкина М.Ю. Липецк 2011 8 класс
Основные возможности среды Altium Designer
Как получить 100 горячих кандидатов в бизнес из ВК за 24 часа
Программный продукт Call Office
For x in range
Forms - формы
Реляционные базы данных
Виртуальная выставка Нет коррупции
Использование ИКТ в системе формирования интереса школьника к занятиям физической культуры
Аттестационная работа. Программа внеурочной деятельности общеинтеллектуального направления Проектируем виртуальные экскурсии
Презентация "Создание Web - документов" - скачать презентации по Информатике
Алгоритмы и основы языка программирования Тurbo Рascal 7.0. (Лекция 7.2)
Сетевой уровень как средство построения больших сетей
Apache HTTP-сервер
Количество информации
Художники. База данных
Растровое кодирование графической информации
Вы можете прислать нам Вашу презентацию и мы опубликуем ее на сайте.
Обратная связь
Для правообладателей
Email: Нажмите что бы посмотреть