1. 3 Designing applications
Objektorienterade applikationer d2, förel. 3
3 Designing applications
(BK chap. 15)
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2. Main concepts to be covered
Objektorienterade applikationer d2, förel. 3
Main concepts to be covered
OOA and OOD
Discovering classes
CRC cards
Designing interfaces
Development process models
Modeling languages
Modeling in UML
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3. Objektorienterade applikationer d2, förel. 3
OOA and OOD
Object Oriented Analysis
Identifies the entities (objects) of a system, their relationships, and cooperation.
Focus on “what” rather than “how”.
Object Oriented Design
Detailed design
Data representation, method signatures,…
System design
Platforms, languages, environment, hardware,…
Kravaanalysen kommer först
den ingår inte I OOA.
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4. Object oriented analysis
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Object oriented analysis
A large and complex area.
The verb/noun method is suitable for relatively small problems.
CRC cards support the analysis.
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5. Objektorienterade applikationer d2, förel. 3
The verb/noun method
The nouns in a description refer to ‘things’.
A source of classes and objects.
The verbs refer to actions.
A source of interactions between objects.
Actions are behavior, and hence methods.
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6. Objektorienterade applikationer d2, förel. 3
A problem description
The cinema booking system should store seat bookings for
multiple theatres.
Each theatre has seats arranged in rows.
Customers can reserve seats and are given a row number
and seat number.
They may request bookings of several adjoining seats.
Each booking is for a particular show (i.e., the screening of
a given movie at a certain time).
Shows are at an assigned date and time, and scheduled in a
theatre where they are screened.
The system stores the customers’ telephone number.
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7. Objektorienterade applikationer d2, förel. 3
Nouns and verbs
Cinema booking system
Stores (seat bookings)
Stores (telephone number)
Theatre
Has (seats)
Movie
Customer
Reserves (seats)
Is given (row number, seat number)
Requests (seat booking)
Time
Date
Seat booking
Show
Is scheduled (in theatre)
Seat
Seat number
Telephone number
Row
Row number
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8. Objektorienterade applikationer d2, förel. 3
Using CRC cards
First described by Kent Beck and Ward Cunningham.
Each index card records:
A class name.
The class’s responsibilities.
The class’s collaborators.
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9. Objektorienterade applikationer d2, förel. 3
A CRC card
Class name Collaborators Responsibilities
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10. Objektorienterade applikationer d2, förel. 3
A partial example
CinemaBookingSystem Collaborators Can find shows by title and Show day. Stores collection of shows. Collection
Retrieves and displays show
details. ...
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11. Objektorienterade applikationer d2, förel. 3
Scenarios
An activity that the system has to carry out or support.
Sometimes known as use cases.
Used to discover and record object interactions (collaborations).
Can be performed as a group activity.
Icketeknisk aktivitet
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12. Objektorienterade applikationer d2, förel. 3
Scenario analysis
Scenarios serve to check the problem description is clear and complete.
Sufficient time should be taken over the analysis.
The analysis will lead into design.
Spotting errors or omissions here will save considerable wasted effort later.
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13. Objektorienterade applikationer d2, förel. 3
Class design
Scenario analysis helps to clarify application structure.
Each card maps to a class.
Collaborations reveal class cooperation/object interaction.
Responsibilities reveal public methods.
And sometimes fields; e.g. “Stores collection ...”
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14. Designing class interfaces
Objektorienterade applikationer d2, förel. 3
Designing class interfaces
Replay the scenarios in terms of method calls, parameters and return values.
Note down the resulting signatures.
Create outline classes with public-method stubs.
Careful design is a key to successful implementation.
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15. Objektorienterade applikationer d2, förel. 3
Documentation
Write class comments.
Write method comments.
Describe the overall purpose of each.
Documenting now ensures that:
The focus is on what rather than how.
That it doesn’t get forgotten!
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16. Objektorienterade applikationer d2, förel. 3
Cooperation
Team-working is likely to be the norm not the exception.
Documentation is essential for team working.
Clean O-O design, with loosely-coupled components, also supports cooperation.
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17. Objektorienterade applikationer d2, förel. 3
Prototyping
Supports early investigation of a system.
Early problem identification.
Incomplete components can be simulated.
E.g. always returning a fixed result.
Avoid random behavior which is difficult to reproduce.
GUI-prototyp utan underliggande intelligens
- eller simulerad sådan
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18. Development process models
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Development process models
Waterfall model
Analysis
Design
Implementation
Unit testing
Integration testing
Delivery
No provision for iteration.
Denna modell har svårt att klara förändringskrav.
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19. Development process models (2)
Objektorienterade applikationer d2, förel. 3
Development process models (2)
Iterative incremental development
Use early prototyping.
Frequent client interaction.
Iteration over:
Analysis
Design
Prototype
Client feedback
A growth model is the most realistic.
Milstolpar <-> inkrement
Inkrement – en väldefinierad portion funktionalitet.
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20. Graphical modeling languages
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Graphical modeling languages
A modeling language has a graphical syntax (and a more or less well defined semantics).
Graphical modeling focus on conceptual aspects of a design.
OMT = Object Modeling Technique (Michael Blaha,Jim Rumbaugh, William Premerlani)
Booch (Grady Booch)
UML = Unified Modeling Language (Jacobson,...)
Hög abstraktionsnivå I början.
Man kan även beskriva vissa implementeringsaspekter.
Modellering != programmering?
UML -> programmeringsspråk?
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21. Objektorienterade applikationer d2, förel. 3
UML diagram types
Static design view
Class diagrams (static relations)
Component diagrams (modularization)
Deployment diagrams (run-time config.)
Dynamic design view
Use case diagrams (user level behavior)
Scenario diagrams (object cooperation)
State diagrams (individual object behavior)
Det finns massor här.
Vi skummar bara lite på ytan.
Aktivitetsdiagram
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22. Objektorienterade applikationer d2, förel. 3
Class diagrams
Class icons
Type relationships
Inheritance (“is a”)
Implementation
Object relationships
Dependency
Association (“knows”)
Aggregation (“has”)
Composition (“contains”)
ClassName
Vi har sett en del klassdiagram.
Några kommentarer om skillnader mellan olika relationer.
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23. Inheritance relationships
Objektorienterade applikationer d2, förel. 3
Inheritance relationships
Superclass
Subclass
Superinterface
Subinterface
Interface
Implementation
Class extension
Interface extension
Interface implementation
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24. Objektorienterade applikationer d2, förel. 3
Class icons
Class icon
Stereotype
Class name
<<abstract>>
Thing
- size : int
+ getSize() : int
# setSize(n:int) : void
Variables
Access modifier
Private –
Protected #
Public
Methods
Man kan ta med olika mycket detaljer I olika ikoner och diagram.
Ta inte med attribut som motsvaras av en relationspil.
Return type
Parameter
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25. Object relation properties
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Object relation properties
Multiplicity
Exactly x x
Zero or more *
Range x to y x..y
x or more x..
Name
Navigability *
update
owned
owner
Ingen pil = navigerbar i båda riktningarna
Multiplicitet kan sättas ut i båda ändarna
Role
Role
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26. Aggregation and composition
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Aggregation and composition
whole
Aggregate
Component
Aggregate
Component
Aggregation
Composition
part
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27. Aggregation and composition (2)
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Aggregation and composition (2)
University
Student
Department * 1
A department belongs to a university.
The life time of a department is bounded by the life time of the university to which it belongs.
(strong aggregation)
The life time of a student is independent of the life time of the department.
(weak aggregation)
Vid starkt aggregat är multipliciteten alltid 1 på aggregatsidan.
Vid svagt aggregat kan den vara *
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28. Aggregation vs inheritance
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Aggregation vs inheritance
Sometimes aggregation is a natural alternative to inheritance.
Ask the question:
Which is most natural to say, that an A has a B or, that an A is a B?
List
Queue
The list is an internal
implementation
detail of this queue.
Is a queue really a list?
Do we want a queue
to provide general list
operations?
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ANIMERA
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29. Aggregation, association and dependency relationships
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Aggregation, association and dependency relationships
Many clients share a server. No client owns the server.
Internal state
Utility
Client * 1
Server
someMethod(Utility x) : void
Borde vi inte ha komposition här?
Servern kan gå ner,men tillståndet överlever på disk tills den kommer upp igen. (Objektströmmar…)
Allmänt:
Rita flera diagram.
Inte allt i ett enda.
Relationer utan klassdetaljer i ett.
Klassdetaljer utan relationer i ett annat.
A server owns it’s internal state. It is not shared by others.
A dependency is more volatile than an association. A server uses the utility temporarily.
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30. Objektorienterade applikationer d2, förel. 3
Use case modeling
Use case view
Captures the behavior of a system as it appears to a user outside the system boundary.
Main inventor - Ivar Jacobson
Actor
External part that interacts with the system.
Idealized user: human, other system, process, ...
Use case
External system behavior, meaningful to an actor.
A piece of interactive functionality as a sequence of messages between an actor and a system.
Ett litet steg mot funktionsorienterat synsätt.
Ett användningsfall skall beskriva en meningsfull tjänst – inte för smått alltså!
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31. Objektorienterade applikationer d2, förel. 3
Use case diagrams
Use case icons
Actor icons
Use case relationships
Generalization
Inclusion
Extension
Participation
use case name
actor name
Ovalen talar bara om att det finns och vad det heter.
Resten finns I ett strukturerat dokument.
Relationerna har vissaberöringspunkter med klassrelationer.
<<include>>
<<extend>>
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32. Use case diagram for a university
Objektorienterade applikationer d2, förel. 3
Use case diagram for a university
University system
System boundary
registration
teacher
student
course activities
examination
secretary
report credits
Aktörer kan vara andra system.
LADOK kanske borde vara en aktör här?
Läs inte dessa diagram som flödesplaner!
view credits
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33. Objektorienterade applikationer d2, förel. 3
Use case parts
Whole use case
course activities
<<include>>
<<include>>
<<include>>
attend lab supervision
attend lectures
do home work
Sådana delar kan återanvändas i andra användningsfall:
Ex. Autentiseringsproceduren i en bankomat kan användas för flera olika tjänster.
Use case fragment
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34. Generalization – specialization and extension
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Generalization – specialization and extension
examination
<<include>>
<<include>>
Generalization
submit labs
do exam
Specialization
<<extend>>
submit bonus
do written exam
do oral exam
Det utvidgade användningsfallet “vet inte om utvidgningen” – men man kör hela.
Use case extension
One of the special use cases may be substituted for the general use case.
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35. Objektorienterade applikationer d2, förel. 3
Scenario diagrams
A scenario diagram visualizes how cooperating objects implement a use case, or part of a use case.
There are two main types of scenario diagrams
Cooperation diagrams
Focus on object cooperation aspects.
Sequence diagrams
Visualize the temporal orderings of messages sent between cooperating objects.
Användbart till lite av varje
Man kan göra informella sådana för att beskriva allt möjligt.
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36. Objektorienterade applikationer d2, förel. 3
Sequence diagrams
System boundary
Instance
Instance name
Class
external actor
t i m e
: Client
server : Server
Time line
select(x)
Message
Activation
requestX()
Return
Tydliggör objektsamarbete I ett användningsfall.
Användbara för att få fram metoder och parametrar – och ibland nya klasser.
Finns mer här
skapa objekt
alternativt flöde
Destruction
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ANIMERA
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37. Ex. A cash machine scenario
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Ex. A cash machine scenario
customer
: CardUnit
: CPU
: Keyboard
: GUI
: BillFeader
: ReceiptPrinter
insert(card)
check(card)
msg(”type PID”)
type(PID)
check()
msg(”select amount”)
type(amount)
Focus of control
Ganska svag formalism
Beskriver ett möjligt scenario
Lite fusk här, men visar idén.
Synkront – asynkront
req(amount)
deliver($)
Return arrows omitted in lower part
print(receipt)
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38. Objektorienterade applikationer d2, förel. 3
Review
Class collaborations and object interactions must be identified.
CRC analysis supports this.
An iterative approach to design, analysis and implementation can be beneficial.
Regard software systems as entities that will grow and evolve over time.
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39. Objektorienterade applikationer d2, förel. 3
Review
Work in a way that facilitates collaboration with others.
Design flexible, extendible class structures.
Being aware of existing design patterns will help you to do this.
Continue to learn from your own and others’ experiences.
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