slide 10a.1 © the mcgraw-hill companies, 2005 object-oriented and classical software engineering...
TRANSCRIPT
Slide 10A.1
© The McGraw-Hill Companies, 2005
Object-Oriented and Classical Software
Engineering
Sixth Edition, WCB/McGraw-Hill, 2005
Slide 10A.2
© The McGraw-Hill Companies, 2005
CHAPTER 10 — Unit A
REQUIREMENTS
Slide 10A.3
© The McGraw-Hill Companies, 2005
REQUIREMENTS- Overview
Determining what the client needs Overview of the requirements workflow Understanding the domain The business model Initial requirements Initial understanding of the domain: The Osbert
Oglesby case study Initial business model: The Osbert Oglesby case
study Initial requirements: The Osbert Oglesby case
study
Slide 10A.4
© The McGraw-Hill Companies, 2005
Overview (contd)
Continuing the requirements workflow: The Osbert Oglesby case study
The test workflow: The Osbert Oglesby case study The classical requirements phase Rapid prototyping Human factors Reusing the rapid prototype CASE tools for the requirements workflow Metrics for the requirements workflow Challenges of the requirements workflow
Slide 10A.5
© The McGraw-Hill Companies, 2005
The Aim of the Requirements Workflow
To answer the question:
What must the product be able to do?
Slide 10A.6
© The McGraw-Hill Companies, 2005
10.1 Determining What the Client Needs
Misconception We must determine what the client wants
“I know you believe you understood what you think I said, but I am not sure you realize that what you heard is not what I meant!”
We must determine what the client needs
Slide 10A.7
© The McGraw-Hill Companies, 2005
Determining What the Client Needs (contd)
It is hard for a systems analyst to visualize a software product and its functionalityThe problem is far worse for the client
A skilled systems analyst is needed to elicit (bring out) the appropriate information from the client
The client is the only source of this information
Slide 10A.8
© The McGraw-Hill Companies, 2005
Determining What the Client Needs (contd)
The solution:Obtain initial information from the client Use this initial information as input to the Unified
ProcessFollow the steps of the Unified Process to determine the
client’s real needs
Slide 10A.9
© The McGraw-Hill Companies, 2005
10.2 Overview of the Requirements Workflow
First, gain an understanding of the application domain (or domain, for short)The specific environment in which the target product is to
operate
Second, build a business modelModel the client’s business processes
Third, use the business model to determine the client’s requirements
Iterate the above steps
Slide 10A.10
© The McGraw-Hill Companies, 2005
Definitions
Discovering the client’s requirementsRequirements elicitation (or requirements capture)Methods include interviews and surveys
Refining and extending the initial requirements Requirements analysis
Slide 10A.11
© The McGraw-Hill Companies, 2005
10.3 Understanding the Domain
Every member of the development team must become fully familiar with the application domainCorrect terminology is essential
Construct a glossaryA list of technical words used in the domain, and their
meanings
Slide 10A.12
© The McGraw-Hill Companies, 2005
10.4 Business Model
A business model is a description of the business processes of an organization
The business model gives an understanding of the client’s business as a wholeThis knowledge is essential for advising the client
regarding computerization
The systems analyst needs to obtain a detailed understanding of the various business processes Different techniques are used, primarily interviewing
Slide 10A.13
© The McGraw-Hill Companies, 2005
10.4.1 Interviewing
The requirements team meet with the client and users to extract all relevant information
Slide 10A.14
© The McGraw-Hill Companies, 2005
Interviewing (contd)
There are two types of questionsClose-ended questions require a specific answerOpen-ended questions are asked to encourage the
person being interviewed to speak out
There are two types of interviews In a structured interview, specific preplanned questions
are asked, frequently close-ended In an unstructured interview, questions are posed in
response to the answers received, frequently open-ended
Slide 10A.15
© The McGraw-Hill Companies, 2005
Interviewing (contd)
Interviewing is not easyAn interview that is too unstructured will not yield much
relevant informationThe interviewer must be fully familiar with the
application domainThe interviewer must remain open-minded at all times
After the interview, the interviewer must prepare a written report It is strongly advisable to give a copy of the report to the
person who was interviewed
Slide 10A.16
© The McGraw-Hill Companies, 2005
10.4.2 Other Techniques
Interviewing is the primary technique
A questionnaire is useful when the opinions of hundreds of individuals need to be determined
Examination of business forms shows how the client currently does business
Slide 10A.17
© The McGraw-Hill Companies, 2005
Other Techniques (contd)
Direct observation of the employees while they perform their duties can be usefulVideotape cameras are a modern version of this
techniqueBut, it can take a long time to analyze the tapesEmployees may view the cameras as an unwarranted
invasion of privacy
Slide 10A.18
© The McGraw-Hill Companies, 2005
10.4.3 Use Cases
+A use case models an interaction (business activity) between the software product itself and the users of that software product (actors)
Example:
Figure 10.1
Slide 10A.19
© The McGraw-Hill Companies, 2005
Use Cases (contd)
An actor is a member of the world outside the software product
It is usually easy to identify an actorAn actor is frequently a user of the software product
In general, an actor plays a role with regard to the software product. This role isAs a user; orAs an initiator; orAs someone who plays a critical part in the use case
Slide 10A.20
© The McGraw-Hill Companies, 2005
Use Cases (contd)
A user of the system can play more than one role
Example: A customer of the bank can beA Borrower or A Lender
Slide 10A.21
© The McGraw-Hill Companies, 2005
Use Cases (contd)
Conversely, one actor can be a participant in multiple use cases
Example: A Borrower may be an actor in The Borrow Money use case;The Pay Interest on Loan use case; and The Repay Loan Principal use case
Also, the actor Borrower may stand for many thousands of bank customers
Slide 10A.22
© The McGraw-Hill Companies, 2005
Use Cases (contd)
An actor need not be a human being
Example: An e-commerce information system has to interact with the credit card company information systemThe credit card company information system is an actor
from the viewpoint of the e-commerce information system
The e-commerce information system is an actor from the viewpoint of the credit card company information system
Slide 10A.23
© The McGraw-Hill Companies, 2005
Use Cases (contd)
A potential problem when identifying actorsOverlapping actors
Example: Hospital software productOne use case has actor NurseA different use case has actor Medical StaffBetter:
Actors: Physician and Nurse
Slide 10A.24
© The McGraw-Hill Companies, 2005
Use Cases (contd)
Alternatively: Actor Medical Staff with two specializations: Physician
and Nurse
Figure 10.2
Slide 10A.25
© The McGraw-Hill Companies, 2005
10.5 Initial Requirements
The initial requirements are based on the initial business model
Then they are refined
The requirements are dynamic — there are frequent changesMaintain a list of likely requirements, together with use
cases of requirements approved by the client
Slide 10A.26
© The McGraw-Hill Companies, 2005
Initial Requirements (contd)
There are two categories of requirements
A functional requirement specifies an action that the software product must be able to performOften expressed in terms of inputs and outputs
A nonfunctional requirement specifies properties of the software product itself, such as Platform constraintsResponse timesReliability
Slide 10A.27
© The McGraw-Hill Companies, 2005
Initial Requirements (contd)
Functional requirements are handled as part of the requirements and analysis workflows
Some nonfunctional requirements have to wait until the design workflowThe detailed information for some nonfunctional
requirements is not available until the requirements and analysis workflows have been completed
Slide 10A.28
© The McGraw-Hill Companies, 2005
10.6 Initial Understanding of the Domain: The Osbert Oglesby Case Study
Osbert Oglesby, Art Dealer, needs a software product to assist him in buying and selling paintings
Obtaining domain knowledge is the first step
Osbert is interviewed to obtain the relevant information
This information is put into a glossary (see next slide)
Slide 10A.29
© The McGraw-Hill Companies, 2005
Glossary: The Osbert Oglesby Case Study
Figure 10.3
Slide 10A.30
© The McGraw-Hill Companies, 2005
10.7 Initial Business Model: The Osbert Oglesby Case Study
Osbert wants an software product, running on his laptop computer, that will Determine the maximum price he should pay for a
paintingDetect new trends in the art market as soon as possible
To do this, the software product needs to keep a record of all purchases and all sales
Slide 10A.31
© The McGraw-Hill Companies, 2005
Initial Business Model: The Osbert Oglesby Case Study (contd)
Currently, Osbert produces reports of annual sales and purchases by handAt only a small additional cost, the software product can
also print these two reports on demand
It is vital to determine the client’s needs up front, and not after the software product has been delivered
Slide 10A.32
© The McGraw-Hill Companies, 2005
Initial Business Model: The Osbert Oglesby Case Study (contd)
Osbert has three business activities: He buys paintingsHe sells paintingsHe produces reports
Slide 10A.33
© The McGraw-Hill Companies, 2005
Initial Business Model: The Osbert Oglesby Case Study (contd)
Buy a Painting use case
Figure 10.4
Slide 10A.34
© The McGraw-Hill Companies, 2005
Initial Business Model: The Osbert Oglesby Case Study (contd)
Sell a Painting use case
Figure 10.5
Slide 10A.35
© The McGraw-Hill Companies, 2005
Initial Business Model: The Osbert Oglesby Case Study (contd)
Produce a Report use case
Figure 10.6
Slide 10A.36
© The McGraw-Hill Companies, 2005
Initial Business Model: The Osbert Oglesby Case Study (contd)
For conciseness, all three use cases are combined into a use-case diagram
Figure 10.7
Slide 10A.37
© The McGraw-Hill Companies, 2005
Initial Business Model: The Osbert Oglesby Case Study (contd)
The only person who uses the current (manual) software product is OsbertOsbert is therefore an actor in all three use cases
The customer may initiate the Buy a Painting or the Sell a Painting use case
The customer plays a critical part in both use cases by providing data entered into the software product by OsbertThe customer is therefore an actor in both these use
cases
Slide 10A.38
© The McGraw-Hill Companies, 2005
Initial Business Model: The Osbert Oglesby Case Study (contd)
Next, the use cases have to be annotated
Here are the initial use-case descriptions
Slide 10A.39
© The McGraw-Hill Companies, 2005
Initial Business Model: The Osbert Oglesby Case Study (contd)
Buy a Painting use case
Figure 10.8
Slide 10A.40
© The McGraw-Hill Companies, 2005
Initial Business Model: The Osbert Oglesby Case Study (contd)
Sell a Painting use case
Figure 10.9
Slide 10A.41
© The McGraw-Hill Companies, 2005
Initial Business Model: The Osbert Oglesby Case Study (contd)
Produce a Report use case
Figure 10.10
Slide 10A.42
© The McGraw-Hill Companies, 2005
Continued in Unit 10B