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3 CS 501 Spring 2003 The Waterfall Model Requirements Analysis System design Unit & Integration Testing System Testing Operation & Maintenance Program design Coding Acceptance Testing Requirements Design Implementation
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1 CS 501 Spring 2003
CS 501: Software Engineering
Lecture 17
Object Oriented Design I
2 CS 501 Spring 2003
Administration
New syllabus
Quiz 4 on Thursday, April 3 (no lecture)
Lecture 23 on Wednesday April 16 (evening)
Second presentation and report next week
Sign up. Assignment will be posted shortly
Quiz 3
Collect after class
3 CS 501 Spring 2003
The Waterfall Model
Requirements Analysis
System design
Unit & Integration Testing
System Testing
Operation & Maintenance
Program design
Coding
Acceptance Testing
Requirements
Design
Implementation
4 CS 501 Spring 2003
Program Design
The task of program design is to represent the software system functions in a form that can be transformed into one or more executable programs.
Given a system architecture, the program design specifies:
• computers and networks• programs, components, packages, classes and class
hierarchies• interfaces, protocols• security mechanisms, operational procedures
5 CS 501 Spring 2003
The Importance of Modeling
• A model is a simplification of reality.
• We build models so that we can better understand the system we are developing.
• We build models of complex system because we cannot comprehend such a system in its entirety.
Models can be informal or formal. The more complex the project the more valuable a formal model becomes.
BRJ
6 CS 501 Spring 2003
Principles of Modeling
• The choice of what models to create has a profound influence on how a problem is attacked and how a solution is shaped.
• Every model can be expressed at different levels of precision.
• The best models are connected to reality.
• No single model is sufficient. Every nontrivial system is best approached through a small set of nearly independent models.
BRJ
7 CS 501 Spring 2003
The Unified Modeling Language
UML is a standard language for modeling software systems
• Serves as a bridge between the requirements specification and the implementation.
• Provides a means to specify and document the design of a software system.
• Is process and programming language independent.
• Is particularly suited to object-oriented program development.
8 CS 501 Spring 2003
Useful Texts
Grady Booch, James Rumbaugh, Ivar Jacobson, The Unified Modeling Language. Addison-Wesley 1999.
Grady Booch, Object-Oriented Analysis and Design with Applications, second edition. Benjamin/Cummings 1994.
Rob Pooley, Perdita Stevens, Using UML Software Engineering with Objects and Components. Addison-Wesley 1999.
9 CS 501 Spring 2003
Rational Rose
Rational Rose is a system for creating and managing UML diagrams.
It is available for all Computer Science Department computers, but you may have to install it.
See: http://adm/Software/purify_install.htm for installation instructions.
See: http://www.rational.com/products/index.jsp for information about the system.
10 CS 501 Spring 2003
Diagrams in UML
A diagram is the graphical representation of a set of elements, usually rendered as a connected graph of vertices (things) and arcs (relationships).
• Class diagram shows a set of classes, interfaces, and collaborations with their relationships.
• Object diagram shows a set of objects and their relationships.
• Use case diagram shows a set of use cases and actors (a special kind of class) and their relationships.
11 CS 501 Spring 2003
Diagrams in UML (continued)
Interaction diagram shows an interaction, consisting of a set of objects and the relationships, including the messages that may be dispatched among them.
=> A sequence diagram emphasizes the time ordering.
=> A collaboration diagram emphasizes the structural organization of the objects that send and receive messages.
12 CS 501 Spring 2003
Diagrams in UML (continued)
• Statechart diagram shows a state machine consisting of states, transitions, events, and activities.
• Activity diagram is a statechart diagram that shows the flow from activity to activity within a system.
• Component diagram shows the organization and dependencies among a set of components.
• Deployment diagram shows the configuration of processing nodes and the components that live on them.
13 CS 501 Spring 2003
Class
Window
originsize
open()close()move()display()
name
attributes
operations
A class is a description of a set of objects that share the same attributes, operations, relationships and semantics.
14 CS 501 Spring 2003
Class Diagrams
Window
originsize
open()close()move()display()
name
attributes
operations
A class is a description of a set of objects that share the same attributes, operations, relationships and semantics.
15 CS 501 Spring 2003
The "Hello, World" Example
import java.awt.Graphics;class HelloWorld extends java.applet.Applet { public void paint (Graphics g) { g.drawString ("Hello, World!", 10, 10); }}
Example from: BJR
16 CS 501 Spring 2003
The HelloWorld Example
HelloWorld
paint()
class
name
operations
17 CS 501 Spring 2003
Annotation
return copy of self
A note is a symbol for rendering constraints and comments attached to an element or a collection of elements.
18 CS 501 Spring 2003
Abstraction for HelloWorld
HelloWorld
paint() g.drawString ("HelloWorld", 0, 10)"
class
name
operations
annotation
19 CS 501 Spring 2003
Notation: Relationships
A dependency is a semantic relationship between two things in which a change to one may effect the semantics of the other.
0..1 *employer employee
An association is a structural relationship that describes a set of links, a link being a connection among objects.
20 CS 501 Spring 2003
Relationships
Parking
Parking Space
location
is_available()
1
0 ... 1
21 CS 501 Spring 2003
Notation: Relationships (continued)
A generalization is a specialization/generalization relationship is which objects of the specialized element (child) are substitutable for objects of the generalized element (parent).
child parent
A realization is a semantic relationship between classifiers, wherein one classifier specifies a contract that another classifier guarantees to carry out.
22 CS 501 Spring 2003
Generalization
Applet
HelloWorld
paint() Graphics
generalization
dependency
Note that the Applet and Graphics classes are shown elided.
23 CS 501 Spring 2003
Notation: Interface
An interface is a collection of operations that specify a service of a class or component, i.e., the externally visible behavior of that element.
ISpelling
24 CS 501 Spring 2003
Class Inheritance Diagram
Object
Component
Container
Panel
Applet
HelloWorld
ImageObserver
interface
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Modeling Classes
Given a real-life system, how do you decide what classes to use?
• What terms do the users and implementers use to describe the system? They are candidates for classes.
• Is each candidate class crisply defined?
• For each class, what is its set of responsibilities? Are the responsibilities evenly balanced among the classes?
• What attributes and operations does each class need to carry out its responsibilities?
26 CS 501 Spring 2003
Noun Identification: A Library Example
The library contains books and journals. It may have several copies of a given book. Some of the books are reserved for short-term loans only. All others may be borrowed by any library member for three weeks. Members of the library can normally borrow up to six items at a time, but members of staff may borrow up to 12 items at one time. Only members of staff may borrow journals.
The system must keep track of when books and journals are borrowed and returned and enforce the rules.
27 CS 501 Spring 2003
Noun Identification: A Library Example
The library contains books and journals. It may have several copies of a given book. Some of the books are reserved for short-term loans only. All others may be borrowed by any library member for three weeks. Members of the library can normally borrow up to six items at a time, but members of staff may borrow up to 12 items at one time. Only members of staff may borrow journals.
The system must keep track of when books and journals are borrowed and returned and enforce the rules.
28 CS 501 Spring 2003
Candidate Classes
Library the name of the systemBookJournalCopyShortTermLoan eventLibraryMemberWeek measureMemberOfLibrary repeatItem book or journalTime abstract termMemberOfStaffSystem general termRule general term
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Relations between Classes
Book is an ItemJournal is an ItemCopy is a copy of a BookLibraryMemberItemMemberOfStaff is a LibraryMember
Is Item needed?
30 CS 501 Spring 2003
Operations
LibraryMember borrows Copy
LibraryMember returns Copy
MemberOfStaff borrows Journal
MemberOfStaff returns Journal
Item not needed yet.
31 CS 501 Spring 2003
Class Diagram
MemberOfStaff
BookCopyJournal is a copy of
1..* 1
LibraryMember
1
0..*0..12
1
on loanon loan
32 CS 501 Spring 2003
Rough Sketch: Wholesale System
A wholesale merchant supplies retail stores from stocks of goods in a warehouse.
What classes would you use to model this business?
33 CS 501 Spring 2003
Rough Sketch: Wholesale System
RetailStore
Warehouse
Order
Invoice
Product
Shipment
Merchant
34 CS 501 Spring 2003
Rough Sketch: Wholesale System
Warehouse
Order
Invoice
Product
MerchantRetailStore
nameaddresscontactInfofinancialInfo
Shipment
Responsibilities-track status of shipped products
Reversal
damaged()return()wrongItem()
responsibility (text field)
35 CS 501 Spring 2003
Expanding a Class: Modeling Financial Information
RetailStore
Transaction1 *association
Invoice
PaymentWhich class is responsible for the financial records for a store?
36 CS 501 Spring 2003
Modeling Invoice
Shipment
Invoice
invoiceNumber
+goodsShipped()-sendInvoice()
goodsShipped
PartsListadornments+ public- private
RetailStore???
invoiceRecord
37 CS 501 Spring 2003
Lessons Learned
Design is empirical. There is no single correct design. During the design process:
• Eliding: Elements are hidden to simplify the diagram
• Incomplete: Elements may be missing.
• Inconsistency: The model may not be consistent
The diagram is not the whole design. Diagrams must be backed up with specifications.
38 CS 501 Spring 2003
Levels of Abstraction
The complexity of a model depends on its level of abstraction:
• High-levels of abstraction show the overall system.
• Low-levels of abstraction are needed for implementation.
Two approaches:
• Model entire system at same level of abstraction, but present diagrams with different levels of detail.
• Model parts of system at different levels of abstraction.
39 CS 501 Spring 2003
Notation: Grouping
A package is a general-purpose mechanism for organizing elements into groups.
Business rules
40 CS 501 Spring 2003
Packaging Classes
applet
awt
lang
HelloWorld
java
Graphics
package
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