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CS 5150 2
Administration
Test 3 is next Monday
The test will cover material from all classes since the beginning of the semester, including next Monday's class.
CS 5150 3
Comments on Assignment 2: Schedules
The schedule must provide time for:
• User testing and revisions
• Program and system testing
• Revision and correction of problems discovered during testing
• Deployment
• Handover and acceptance testing
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Architectural Style - Model/View/Controller
ModelController View
Example: Control of a unmanned model aircraft
Controller: Receives instrument readings from the aircraft and sends controls signals to the aircraft.
Model: Translates data received from and sent to the aircraft, and instructions from the user into a model of flight performance. Uses domain knowledge about the aircraft and flight.
View: Displays information about the aircraft to the user and transmits instructions to the model.
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Model/View/Controller: Autonomous Land Vehicle
Sensors
GPS
Sonar
Laser
Signal processing
Model Control signals
Steer
Throttle
Controls
View Model Controller
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Model/View/Controller for Web Applications
1 User interacts with the user interface (e.g., presses a mouse button).
2 Controller handles input event from the user interface, (e.g., via a registered handler or callback) and converts the event into appropriate user action.
3 Controller notifies Model of user action, possibly resulting in a change in Model's state (e.g., update shopping cart.).
4 View interacts with Model to generate an appropriate user interface response (e.g., list shopping cart's contents).
5 User interface waits for further user interactions.
from Wikipedia 10/18/2009
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Model/View/Controller for Web Applications
ModelController View
HTMLHTTP
WebBrowser control functions
WebBrowser view
functions
Input events Response
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Program Design in the Modified Waterfall Model
Requirements
System design
Testing
Operation & maintenance
Program design
Implementation (coding)
Acceptance & release
Feasibility study
Requirements
Design
Implementation
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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:
• programs, components, packages, classes and class hierarchies
• interfaces, protocols (where not part of the system architecture)
• algorithms, data structures, security mechanisms, operational procedures
If the program design is done properly, all design decisions should be made before implementation.
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UML Models
UML models (diagrams and specifications) can be used for almost all aspects of program design
• Diagram gives a general overview of the model, showing the principal elements and how they relate to each other.
• Specification provides details about each element of the model. Specification for models used in program design should have sufficient detail that they can be used to write code from.
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Class Diagrams
Window
originsize
open()close()move()display()
name
attributes [local, instance, and class (static) variables]
operations [methods]
responsibilities [optional text]
A class is a description of a set of objects that share the same attributes, operations, relationships, and semantics.
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The "Hello, World!" Applet
import java.awt.Graphics;class HelloWorld extends java.applet.Applet { public void paint (Graphics g) { g.drawString ("Hello, World!", 10, 10); }}
Example from: BJR
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Abstraction for HelloWorld
HelloWorld
paint() g.drawString ("HelloWorld", 0, 10)"
class
name
operations
annotation
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Annotation
some text note
A note is a symbol for rendering constraints and comments attached to an element or a collection of elements.
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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.
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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.
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Generalization
Applet
HelloWorld
paint() Graphics
generalization
dependency
Note that the Applet and Graphics classes are shown elided, i.e., just the name is shown, not the attributes or operations.
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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
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Notation: Package
A package is a general-purpose mechanism for organizing elements into groups.
Business rules
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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?
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Candidate Classes: Application Classes and Solution Classes
• Application classes represent application concepts.
Noun identification is an effective technique to generate candidate application classes.
• Solution classes represent system concepts, e.g., user interface objects, databases, etc.
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Noun Identification for Application Classes: 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.
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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.
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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?
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Operations
LibraryMember borrows Copy
LibraryMember returns Copy
MemberOfStaff borrows Journal
MemberOfStaff returns Journal
Item not needed yet.
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A Possible Class Diagram
MemberOfStaff
BookCopyJournal is a copy of
1..* 1
LibraryMember
1
0..*0..12
1
on loanon loan
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From Candidate Classes to Completed Design
Methods used to move to final design:
Reuse: Wherever possible use existing components, or class libraries. They may need modification.
Restructuring: Change the design to improve, understandability, maintainability, etc. Techniques include merging similar classes, splitting complex classes, etc.
Optimization: Ensure that the system meets anticipated performance requirements, e.g., by changed algorithms or restructuring.
Completion: Fill all gaps, specify interfaces, etc.
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Coupling and Cohesion
Coupling is a measure of the dependencies between two part of a system. If two classes are strongly coupled, it is hard to modify one without modifying the other.
Cohesion is a measure of dependencies within part of a system. If a class contains many closely related functions its cohesion is high.
Aim for high cohesion within classes and weak coupling between them.
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Rough Sketch: Wholesale System
Design is empirical and iterative. The following very artificial example, gives an idea of the process.
Example
A wholesale merchant supplies retail stores from stocks of goods in a warehouse.
What classes would you use to model this business?
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Rough Sketch: Wholesale System
RetailStore
Warehouse
Order
Invoice
Product
Shipment
Merchant
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Rough Sketch: Wholesale System
Warehouse
Order
Invoice
Product
MerchantRetailStore
nameaddresscontactInfofinancialInfo
Shipment
Responsibilities-track status of shipped products
Reversal
damaged()return()wrongItem()
responsibility (text field)
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Expanding a Class: Modeling Financial Information
RetailStore
Transaction1 *association
Invoice
PaymentWhich class is responsible for the financial records for a store?
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Modeling Invoice
Shipment
Invoice
invoiceNumber
+goodsShipped()-sendInvoice()
goodsShipped
PartsListadornments+ public- private
RetailStore???
invoiceRecord
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Lessons Learned
Design is empirical. There is no single correct design.
During the design process:
• Eliding: Elements are hidden to simplify the diagram
• Incomplete: During the early part of the design process, elements may be missing.
• Inconsistency: During the early part of the design process, the model may not be consistent
The diagram is not the whole design. Diagrams must be backed up with specifications.
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An Exam Question: Object Oriented Design
A system generates weather maps using data collected from
unattended weather stations. Each weather station collects
meteorological data and produces summaries of the data.
On request, it sends the summary information to an area
computer. The area computer uses a database of digitized
maps to generate a set of local weather maps.
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Exam Question: Noun Identification
A system generates weather maps using data collected from
unattended weather stations. Each weather station collects
meteorological data and produces summaries of the data.
On request, it sends the summary information to an area
computer. The area computer uses a database of digitized
maps to generate a set of local weather maps.
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Exam Question: Candidate Classes
System general term
WeatherMap
Data same as MeteorologicalData
WeatherStation is this a general term?
MeteorologicalData how does this relate to WeatherStation?
DataSummary how does this relate to MeteorologicalData?
AreaComputer hardware
Database general term
DigitizedMap
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Exam Question: Observations about the Candidate Classes
WeatherMap is a DigitizedMapis derived from 1...* DataSummary
WeatherStation has a set of MeteorologicalData
MeteorologicalData
DataSummary is derived from MeteorologicalData
DigitizedMap
Can Meteorological Data be an attribute of WeatherStation?Can DataSummary be combined with WeatherMap?
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Exam Question: Attributes and Operations
WeatherStation
locationmetereologicalData
collectData()getSummary()
WeatherMap
locationdate-timegeographicDataweather
gatherData()printMap()DigitizedMap
locationgeographicData
printMap()
Or should MetereologicalData be a separate object?
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