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Introduction. Object-oriented design. Unified Modeling Language (UML). System modeling. Need languages to describe systems: useful across several levels of abstraction; understandable within and between organizations. Block diagrams are a start, but don’t cover everything. - PowerPoint PPT Presentation
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© 2008 Wayne Wolf Overheads for Computers as Components, 2 nd ed. Introduction Object-oriented design. Unified Modeling Language (UML).
Transcript
Page 1: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Introduction

Object-oriented design.Unified Modeling Language (UML).

Page 2: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

System modeling

Need languages to describe systems: useful across several levels of

abstraction; understandable within and between

organizations.Block diagrams are a start, but don’t

cover everything.

Page 3: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Object-oriented design

Object-oriented (OO) design: A generalization of object-oriented programming.

Object = state + methods. State provides each object with its own

identity. Methods provide an abstract interface

to the object.

Page 4: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Objects and classes

Class: object type.Class defines the object’s state

elements but state values may change over time.

Class defines the methods used to interact with all objects of that type. Each object has its own state.

Page 5: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

OO design principles

Some objects will closely correspond to real-world objects. Some objects may be useful only for

description or implementation.Objects provide interfaces to

read/write state, hiding the object’s implementation from the rest of the system.

Page 6: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

UML

Developed by Booch et al.Goals:

object-oriented; visual; useful at many levels of abstraction; usable for all aspects of design.

Page 7: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

UML object

d1: Display

pixels: array[] of pixelselementsmenu_items

pixels is a2-D array

comment

object nameclass name

attributes

Page 8: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

UML class

Display

pixelselementsmenu_items

mouse_click()draw_box

operations

class name

Page 9: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

The class interface

The operations provide the abstract interface between the class’s implementation and other classes.

Operations may have arguments, return values.

An operation can examine and/or modify the object’s state.

Page 10: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Choose your interface properly

If the interface is too small/specialized: object is hard to use for even one application; even harder to reuse.

If the interface is too large: class becomes too cumbersome for designers

to understand; implementation may be too slow; spec and implementation are probably buggy.

Page 11: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Relationships between objects and classes

Association: objects communicate but one does not own the other.

Aggregation: a complex object is made of several smaller objects.

Composition: aggregation in which owner does not allow access to its components.

Generalization: define one class in terms of another.

Page 12: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Class derivation

May want to define one class in terms of another. Derived class inherits attributes,

operations of base class.

Derived_class

Base_class

UMLgeneralization

Page 13: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Class derivation example

Display

pixelselementsmenu_items

pixel()set_pixel()mouse_click()draw_box

BW_display Color_map_display

baseclass

derived class

Page 14: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Multiple inheritance

Speaker Display

Multimedia_display

base classes

derived class

Page 15: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Links and associations

Link: describes relationships between objects.

Association: describes relationship between classes.

Page 16: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Link example

Link defines the contains relationship:

message

msg = msg1length = 1102

message

msg = msg2length = 2114

message set

count = 2

Page 17: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Association example

message

msg: ADPCM_streamlength : integer

message set

count : integer

0..* 1

contains

# contained messages # containing message sets

Page 18: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Stereotypes

Stereotype: recurring combination of elements in an object or class.

Example: <<foo>>

Page 19: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Behavioral description

Several ways to describe behavior: internal view; external view.

Page 20: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

State machines

a b

state state name

transition

Page 21: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Event-driven state machines

Behavioral descriptions are written as event-driven state machines. Machine changes state when receiving

an input.An event may come from inside or

outside of the system.

Page 22: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Types of events

Signal: asynchronous event.Call: synchronized communication.Timer: activated by time.

Page 23: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Signal event

<<signal>>mouse_click

leftorright: buttonx, y: position

declaration

a

b

mouse_click(x,y,button)

event description

Page 24: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Call event

c d

draw_box(10,5,3,2,blue)

Page 25: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Timer event

e f

tm(time-value)

Page 26: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Example state machine

regionfound

got menuitem

calledmenu item

foundobject

objecthighlighted

start

finish

mouse_click(x,y,button)/find_region(region)

input/outputregion = menu/which_menu(i) call_menu(I)

region = drawing/find_object(objid) highlight(objid)

Page 27: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Sequence diagram

Shows sequence of operations over time.

Relates behaviors of multiple objects.

Page 28: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Sequence diagram example

m: Mouse d1: Display u: Menu

mouse_click(x,y,button)which_menu(x,y,i)

call_menu(i)

time

Page 29: Introduction

© 2008 Wayne WolfOverheads for Computers as

Components, 2nd ed.

Summary

Object-oriented design helps us organize a design.

UML is a transportable system design language. Provides structural and behavioral

description primitives.


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