Object-Oriented Software Engineering
Practical Software Development using UML and Java
Chapter 4,
Developing Requirements
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 2
4.1 Domain Analysis
The process by which a software engineer learns about
the domain to better understand the problem:
? The domain is the general field of business or
technology in which the clients will use the software
? A domain expert is a person who has a deep knowledge
of the domain
Benefits of performing domain analysis:
? Faster development
? Better system
? Anticipation of extensions
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 3
Domain Analysis document
A,Introduction
B,Glossary
C,General knowledge about the domain
D,Customers and users
E,The environment
F,Tasks and procedures currently performed
G,Competing software
H,Similarities to other domains
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 4
Re qu i r e m e nt s
m us t b e d e t e rm i ne d
Cl i e nt s ha ve pro duc e d
re qui re m e nt s
N e w
de ve l opm e nt
E vol ut i on o f
e x i s t i ng s ys t e m
A B
C D
4.2 The Starting Point for Software Projects
green field project
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 5
4.3 Defining the Problem and the Scope
A problem can be expressed as,
? A difficulty the users or customers are facing,
? Or as an opportunity that will result in some benefit such
as improved productivity or sales,
The solution to the problem normally will entail
developing software
A good problem statement is short and succinct
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 6
Defining the Scope
Narrow the scope by defining a more precise problem
? List all the things you might imagine the system doing
— Exclude some of these things if too broad
— Determine high-level goals if too narrow
Example,A university registration systemI n i t i a l l i st o f p r o b l e ms
w i t h v e r y b r o a d sc o p e
N a r r o w e d
sc o p e
S c o p e o f
a n o t h e r sy st e m
e x am s ch e d u l i n g
r o o m a l l o c a t i o n
f e e p a y m e n t
b r o w si n g c o u r se s
r e g i s t e r i n g
e x am s ch e d u l i n g
r o o m a l l o c a t i o n
f e e p a y m e n t
b r o w si n g c o u r se s
r e g i s t e r i n g
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 7
4.4 What is a Requirement
Requirement,A statement about the proposed system
that all stakeholders agree must be made true in order
for the customer’s problem to be adequately solved.
? Short and concise piece of information
? Says something about the system
? All the stakeholders have agreed that it is valid
? It helps solve the customer’s problem
A collection of requirements is a requirements document.
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 8
4.5 Types of Requirements
Functional requirements
? Describe what the system should do
Non-functional requirements
? Constraints that must be adhered to during development
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 9
Functional requirements
? What inputs the system should accept
? What outputs the system should produce
? What data the system should store that other systems
might use
? What computations the system should perform
? The timing and synchronization of the above
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 10
Non-functional requirements
All must be verifiable
Three main types
1,Categories reflecting,usability,efficiency,reliability,
maintainability and reusability
— Response time
— Throughput
— Resource usage
— Reliability
— Availability
— Recovery from failure
— Allowances for maintainability and enhancement
— Allowances for reusability
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 11
Non-functional requirements
2,Categories constraining the environment and
technology of the system.
— Platform
— Technology to be used
3,Categories constraining the project plan and
development methods
— Development process (methodology) to be used
— Cost and delivery date
- Often put in contract or project plan instead
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 12
4.6 Some Techniques for Gathering and
Analysing Requirements
Observation
? Read documents and discuss requirements with users
? Shadowing important potential users as they do their work
— ask the user to explain everything he or she is doing
? Session videotaping
Interviewing
? Conduct a series of interviews
— Ask about specific details
— Ask about the stakeholder’s vision for the future
— Ask if they have alternative ideas
— Ask for other sources of information
— Ask them to draw diagrams
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 13
Gathering and Analysing Requirements...
Brainstorming
? Appoint an experienced moderator
? Arrange the attendees around a table
? Decide on a ‘trigger question’
? Ask each participant to write an answer and pass the
paper to its neighbour
Joint Application Development (JAD) is a technique based on intensive
brainstorming sessions
!
!
! !
!
!
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 14
Gathering and Analysing Requirements...
Prototyping
? The simplest kind,paper prototype,
— a set of pictures of the system that are shown to
users in sequence to explain what would happen
? The most common,a mock-up of the system’s UI
— Written in a rapid prototyping language
— Does not normally perform any computations,
access any databases or interact with any other
systems
— May prototype a particular aspect of the system
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 15
Gathering and Analysing Requirements...
Informal use case analysis
? Determine the classes of users that will use the facilities
of this system (actors)
? Determine the tasks that each actor will need to do with
the system
More on use cases in Chapter 7
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 16
4.7 Types of Requirements Document
? Requirements documents for
large systems are normally
arranged in a hierarchy
Requirements
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subsy stem 1 subsy stem 2
Requirements
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Requirements
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Requirements
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Two extremes:
An informal outline of the requirements using a few
paragraphs or simple diagrams
requirements definition
A long list of specifications that contain thousands of
pages of intricate detail
requirements specification
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 17
Level of detail required in a requirements
document
? How much detail should be provided depends on:
— The size of the system
— The need to interface to other systems
— The readership
— The stage in requirements gathering
— The level of experience with the domain and the
technology
— The cost that would be incurred if the requirements
were faulty
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 18
4.8 Reviewing Requirements
? Each individual requirement should
— Have benefits that outweigh the costs of development
— Be important for the solution of the current problem
— Be expressed using a clear and consistent notation
— Be unambiguous
— Be logically consistent
— Lead to a system of sufficient quality
— Be realistic with available resources
— Be verifiable
— Be uniquely identifiable
— Does not over-constrain the design of the system
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 19
Requirements documents...
? The document should be:
— sufficiently complete
— well organized
— clear
— agreed to by all the stakeholders
? Traceability:
D e s i g n
d o c um e nt
.,,, du e t o
r e qu i r e m e nt 1,2
R e q u i r e m e n t s
d o c um e nt
1, 1 X X X X
.,,, b e ca u s e
1, 2 Y Y Y Y
r at i on al e
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 20
Requirements document...
A,Problem
B,Background information
C,Environment and system models
D,Functional Requirements
E,Non-functional requirements
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 21
4.9 Managing Changing Requirements
Requirements change because:
? Business process changes
? Technology changes
? The problem becomes better understood
Requirements analysis never stops
? Continue to interact with the clients and users
? The benefits of changes must outweigh the costs,
— Certain small changes (e.g,look and feel of the UI) are usually
quick and easy to make at relatively little cost,
— Larger-scale changes have to be carefully assessed
- Forcing unexpected changes into a partially built system will
probably result in a poor design and late delivery
? Some changes are enhancements in disguise
— Avoid making the system bigger,only make it better
? Lethbridge/Laganière 2001 Chapter 4,Developing requirements 22
4.13 Difficulties and Risks in Domain and
Requirements Analysis
? Lack of understanding of the domain or the real problem
— Do domain analysis and prototyping
? Requirements change rapidly
— Perform incremental development,build flexibility into the
design,do regular reviews
? Attempting to do too much
— Document the problem boundaries at an early stage,carefully
estimate the time
? It may be hard to reconcile conflicting sets of requirements
— Brainstorming,JAD sessions,competing prototypes
? It is hard to state requirements precisely
— Break requirements down into simple sentences and review
them carefully,look for potential ambiguity,make early
prototypes