Rapid software development. Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 17 Slide 1

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Objectives

z To explain how an iterative incremental z To explain how an iterative, incremental

development process leads to faster delivery of more useful software

z To discuss the essence of agile development

methods

T l i th i i l d ti f

z To explain the principles and practices of

extreme programming

z To explain the roles of prototyping in the z To explain the roles of prototyping in the

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Rapid software development

z Because of rapidly changing business z Because of rapidly changing business

environments, businesses have to respond to new opportunities and competition.

z This requires software and rapid

development and delivery is not often the most critical requirement for software

most critical requirement for software systems.

z Businesses may be willing to accept lower y g p

quality software if rapid delivery of essential functionality is possible.

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Requirements

z Because of the changing environment it is z Because of the changing environment, it is

often impossible to arrive at a stable, consistent set of system requirements.y q

z Therefore a waterfall model of development

is impractical and an approach to p pp

development based on iterative specification and delivery is the only way to deliver

ft i kl software quickly.

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Characteristics of RAD processes

z The processes of specification design and z The processes of specification, design and

implementation are concurrent. There is no detailed specification and design documentation is

i i i d minimised.

z The system is developed in a series of increments.

End users evaluate each increment and make End users evaluate each increment and make proposals for later increments.

z System user interfaces are usually developed using

i t ti d l t t

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An iterative development process

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Advantages of incremental development

z Accelerated delivery of customer services z Accelerated delivery of customer services.

Each increment delivers the highest priority functionality to the customer.y

z User engagement with the system. Users

have to be involved in the development p which means the system is more likely to meet their requirements and the users are

itt d t th t

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Problems with incremental development

z Management problems z Management problems

• Progress can be hard to judge and problems hard to find because there is no documentation to demonstrate what has been done.

z Contractual problems

• The normal contract may include a specification; without a specification, different forms of contract have to be used.p , z Validation problems

• Without a specification, what is the system being tested against?

against?

z Maintenance problems

• Continual change tends to corrupt software structure making it more expensive to change and evolve to meet making it more expensive to change and evolve to meet new requirements.

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Prototyping

z For some large systems incremental z For some large systems, incremental

iterative development and delivery may be impractical; this is especially true when p ; p y

multiple teams are working on different sites.

z Prototyping, where an experimental system yp g p y

is developed as a basis for formulating the requirements may be used. This system is

th h th t ifi ti

thrown away when the system specification has been agreed.

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Incremental development and prototyping

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Conflicting objectives

z The objective of incremental development is z The objective of incremental development is

to deliver a working system to end-users. The development starts with those p

requirements which are best understood.

z The objective of j throw-away prototypingy p yp g is to

validate or derive the system requirements. The prototyping process starts with those

i t hi h l d t d requirements which are poorly understood.

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RAD environment tools

z Database programming language z Database programming language z Interface generator

Links to office applications

z Links to office applications z Report generators

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A RAD environment

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Interface generation

z Many applications are based around complex forms z Many applications are based around complex forms

and developing these forms manually is a time-consuming activity.

z RAD environments include support for screen

generation including:

• Interactive form definition using drag and dropInteractive form definition using drag and drop techniques;

• Form linking where the sequence of forms to be presented is specified;

presented is specified;

• Form verification where allowed ranges in form fields is defined.

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Visual programming

z Scripting languages such as Visual Basic z Scripting languages such as Visual Basic

support visual programming where the

prototype is developed by creating a user

p yp p y g

interface from standard items and

associating components with these items

z A large library of components exists to

support this type of development

z These may be tailored to suit the specific

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Visual programming with reuse

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Problems with visual development

z Difficult to coordinate team based z Difficult to coordinate team-based

development.

z No explicit system architecture z No explicit system architecture.

z Complex dependencies between parts of the

program can cause maintainability problems. program can cause maintainability problems.

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COTS reuse

z An effective approach to rapid development z An effective approach to rapid development

is to configure and link existing off the shelf systems.y

z For example, a requirements management

system could be built by using:y y g

• A database to store requirements;

• A word processor to capture requirements and fformat reports;

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Software prototyping

z A prototype is an initial version of a system z A prototype is an initial version of a system

used to demonstrate concepts and try out design options.g p

z A prototype can be used in:

• The requirements engineering process to help q g g p p with requirements elicitation and validation;

• In design processes to explore options and de elop a UI design

develop a UI design;

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Benefits of prototyping

z Improved system usability z Improved system usability.

z A closer match to users’ real needs.

Improved design quality

z Improved design quality. z Improved maintainability.

R d d d l t ff t

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The prototyping process

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Throw-away prototypes

Throw away prototypes

z Prototypes should be discarded after z 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;Prototypes are normally undocumented;

• The prototype structure is usually degraded through rapid change;

Th t t b bl ill t t l

• The prototype probably will not meet normal organisational quality standards.

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Key points

z An iterative approach to software development leads z An iterative approach to software development leads

to faster delivery of software.

z Rapid application development environments

include database programming languages form include database programming languages, form generation tools and links to office applications.

z A throw-away prototype is used to explore

i t d d i ti

requirements and design options.

z When implementing a throw-away prototype, start

with the requirements you least understand; in q y incremental development, start with the best-understood requirements.