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CMPT 275Software EngineeringRequirements Analysis Phase
Requirements Analysis Activity(Identifying Objects, Scenarios)
Janice Regan, 2008-2014
Janice Regan, 2008-2014 2
Requirements Analysis You made a list of functional requirements
Describe the required interactions between the system and its environment (independent of implementation)
You made list of non-functional requirements
QUALITY REQUIREMENTS: Usability, reliability, performance, maintainability
CONSTRAINTS or PSEUDO REQUIREMENTS: Implementation (tools, languages), interface (to external systems), operation (admin, management), packaging, Legal
Janice Regan, 2008-2014 3
Requirements Analysis Now you need to validate and verify your
requirements to assure that they are Complete: all required features must be
described Consistent: no two requirements in the
specification may contradict each other Unambiguous: no requirement can be
interpreted in two different and contradictory ways
Correct: Only features desired by the client / developer are included not unintended extra features (problems)
Janice Regan, 2008-2014 4
Requirements Analysis You continued to build your analysis model
and verify/validate your requirements by Identifying the actors for your system Building a system context diagram to clarify
what is part of your proposed system Identifying and developing informal scenarios
that describe all functions of your system Building use cases based on groups of related
informal scenarios Building a functional model of your system by
investigating relationships between use cases and actors and making a use case diagram
Janice Regan, 2008-2014 5
Requirements Analysis ActivitySoftware
DeveloperClient/User
Update SRS
Questions
Use Case Centered Development (UCCD)
System Context Diagram
Use Cases
Primary Classes
Use Case Diagram
State Diagram
ClassDiagram Scenarios
Janice Regan, 2008-2014 6
UML: Unified Modeling Language Used in this course for analysis models of
System functionality
use case diagrams, use cases and scenarios
Objects and their static relationships
class diagrams, analysis models
Dynamic behavior
state diagrams, collaboration diagrams sequence diagrams
Janice Regan, 2008-2014 7
From use cases to classes Consider one use case, make a class
diagram
1. Identify primary classes to describe the objects involved in a use case
2. Add the relationships between these classes extracted from the use case and / or the requirements satisfied by the use case
Consider additional use cases one by one, adding the additional primary classes and relationships between classes
Janice Regan, 2008-2014 8
Primary Classes (objects) Primary Classes are abstractions that describe the
attributes and behaviors of sets of objects According to the rational unified process (RUP)
Primary classes can be of one of three types, Primary Entity classes represent entities
(objects) present in conceptualization Primary Boundary Classes model interfaces
with external entities (actors) Primary Control Classes model coordination
and sequencing of events/calculations and manipulation of instances of entity classes
Janice Regan, 2008-2014 9
From use cases to classes For the Rational Unified Process
For each use case need at least one interface class
For each used case need one (rarely more) control class
For each use case identify primary entity classes to describe the objects involved
Make a class diagram for each class, then combine. Or make a analysis model for one use case, then add additional use cases
Janice Regan, 2008-2014 10
UML for RUP analysis models Entity Classes
Boundary Classes
Control Classes
Janice Regan, 2008-2014 11
Use case diagram for ATM
Identified primary entity class, account
Bank customer
database
Deposit
Transfer
Withdraw
Janice Regan, 2008-2014 12
account
Example: ATM analysis model dispenser
Cashier interface
Money receptor
withdrawal
transfer
deposit
Bank customer
database
Database query orresponse
Database query orresponse translator
Janice Regan, 2008-2014 13
<<control>>transfer
Example: ATM analysis model
transfer
<<Boundary>>dispenser
<<control>>withdrawal
<<Boundary>>receptor
<<control>>deposit
<<Boundary>>Cashier interface
<<entity>>account
<<Boundary>>Database interface
Janice Regan, 2008-2014 14
Primary Entity Classes Model phenomena or concepts
real life objects or events in the application domain
Other objects, events or concepts handled by the system
Require long term or persistent storage of information describing their instances (objects).
May be passive or active (encapsulate complex behavior related to the information it represents)
Isolate changes to the data they represent
Janice Regan, 2008-2014 15
Identifying Primary Entity Classes
Look for application domain (real world) things and roles that the use case is tracking or manipulating
Look for application domain (real world) events that the use case is tracking or manipulating
Look for recurring references to objects in the use case (recurring nouns)
Janice Regan, 2008-2014 16
Identifying Primary Entity Classes To identify entities that should be represented by
primary classes select nouns from the use case and functional requirements for the use case, inspect each noun (start with recurring nouns) for the following properties Retained information Common attributes (different instances) Multiple attributes Needed services Common operations
Janice Regan, 2008-2014 17
Primary Entity Class ? Retained information
Primary entity classes require long term or persistent storage of information describing their instances (objects).
Consider some examples from the LMS
Patron
Home phone number of each patron
Book
All of these examples require persistent storage of information describing their instances
Janice Regan, 2008-2014 18
Primary Entity Class ? Multiple attributes, Common attributes
Is there more than one attribute (other noun) describing the candidate for primary class?
Home phone number of patron ? NO
Book (title, publisher, call number, …)
Patron (type, home phone #, address …)
Can these attributes be used to describe each object in the candidate primary class?
YES (for Book and Patron)
Janice Regan, 2008-2014 19
Primary Entity Class ?
Needed services, common services Are operations needed to manipulate the
persistent data?
Do such operations need to be available to other classes? Books, patrons and home phone numbers must be
added, removed, and information describing them must be updated. Not enough, what else
Books and patrons must have services to update their values when a patron checks out, checks in, reserves, or requests a book.
Janice Regan, 2008-2014 20
Boundary Classes Model the interaction of a system and its actors
Receiving information from the actor Presenting information to the actor
Represent abstractions of API’s, sensors, input / output devices, external data repositories, forms … Model conceptually what requests and information
exchanged (no details of how or interface, just what)
Each boundary class should be associated with at least on actor. Each actor should be associated with at least one boundary class
Janice Regan, 2008-2014 21
Identifying Boundary Classes Actor interfaces with parts of the system
(ATM client interface)
Identify forms needed to enter data (Ballot entry form)
Identify messages (notices) used to respond to actor input
Janice Regan, 2008-2014 22
Control Classes Control complex sequences of events or
calculations DO NOT DO calculations/tasks USE functionality of classes, coordinating execution order
of tasks done by and events important to the entity classes (>2) involved
Do not usually represent a concrete object in the real world
Do not deal with interaction with actors The lifespan of the object should cover the use
case duration or the duration of the user session
Janice Regan, 2008-2014 23
Support Classes Container classes
e.g.: List and Hash Table classes
Service classes
e.g.: Stream classes
They are not present in conceptualization of software system
The need for these classes identified during design
Janice Regan, 2008-2014 24
Formal Scenario Development Scenarios are derived from use cases
Scenarios are like informal scenarios, but are more formally structured
Use cases are abstract because they do not reference specific values
Scenarios are concrete because they do reference specific and plausible values
Multiple scenarios may be required for a single use case
Janice Regan, 2008-2014 25
Example: Scenario #1 Use Case Name: CheckInResource (#7)
Scenario: Paul returns an overdue book by coming to the library counter.
Preconditions:
Eva the Librarian has successfully gained access to the LMS.
LMS is ready to go (DB has been populated and LMS has been initialized).
Options screen is displayed
Janice Regan, 2008-2014 26
Example: Scenario #1 (cont) Main flow of events:
Patron Paul (a student) comes up to the counter and wishes to return the Quantum Physics book he borrowed the previous semester.
Eva the librarian takes the book Paul is handing out to her selects CHECKINRESOURCE option and types in its valid Dewey call number.
The LMS displays the information related to the Quantum Physics book on the screen and lets Eva know that Paul owes the library $5 (max.).
Janice Regan, 2008-2014 27
Example: Scenario #1 (cont) Main flow of events: (cont)
Eva notifies Paul of his overdue charge and Paul, after searching throughout all his pockets, produces a $5 bill.
Eva makes sure that Paul's record is now clean and that no one has requested the book. Since no one has, Eva verifies by looking at the screen that the book has been checked in properly.
Paul wishes Eva "Good day" and departs.
Janice Regan, 2008-2014 28
Example: Scenario #1 (cont) Post conditions:
Paul’s record is now showing that he has returned the Quantum Physics book and that he has paid the overdue charge. The Quantum Physics book has now a status of "reshelve", today's date as a date of return, date of loan has been cleared and so as the due date.
NO NEED FOR EXCEPTIONAL FLOW OF EVENTS!!!
Each exceptional flow of events would be another scenario
Janice Regan, 2008-2014 29
Example: Scenario #2 Use Case Name: CheckInResource (#7)
Scenario: Paul returns an overdue book by putting it in the return box.
Preconditions: Eva the Librarian has successfully gain access
to the LMS.
LMS is ready to go (DB has been populated and LMS has been initialized).
Janice Regan, 2008-2014 30
Example: Scenario #2 (cont) Main flow of events
Patron Paul (a student) has deposited the Quantum Physics book he borrowed the previous semester in the return box.
Eva the librarian takes the book from the return box and types in its Dewey call number.
Janice Regan, 2008-2014 31
Example: Scenario #2
Main flow of events (Cont)
The LMS displays the information related to the Quantum Physics book on the screen and lets Eva know that the borrowing patron Paul owes the library $5. Eva makes sure that Paul's record reflects such overdue charge.
Then Eva ensures that no one has requested the book. Since no one has, Eva verifies looking at the screen that the book has been checked in properly.
Janice Regan, 2008-2014 32
Example: Scenario #2
Post conditions:
Paul record now showing an overdue charge of $5 (since it was overdue by quite a few weeks). The Quantum Physics book has now a status of "reshelve", today's date as a date of return, date of loan has been cleared and so as the due date.