Oct. 16, 2003 CS 509 - WPI 1

CS 509Design of Software Systems

Lecture #7Thursday, Oct. 16, 2003

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Term Project administrationReturn Quiz #3QuestionsReview of Chapter 7Preview of Chapter 9Get Student Feedback:

How is this course going so far?

Class Format for Today

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MC Project & Quiz #3

Turn in Phase 3 (Design) document

Hand out Phase 4 Assignment

Return Quiz #3 Solutions available on course web

site

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Questions?

About Term ProjectFrom last week’s classFrom the readingAnything else?

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Chapter 7

Object Design

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Object DesignFocus:

Individual objects & hierarchies Interfaces

Challenges: Increasing reuse wherever possible Eliminating as many dependencies as

possible Optimizations to address performance

criteria such as response time or memory usage

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Object Design Activities

Refine analysis & system design models

Identify new objectsClose the gap between application

objects and off-the-shelf components: Identify custom objects Adjust of off-the-shelf components Specify interfaces between classes

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Service Specification

Specify subsystem services identified during system design: Class interfaces Operations, arguments Type signatures Exceptions

Find missing operations and objects

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Component SelectionFind, adapt and use off-the-shelf

componentsClass libraries & 3rd party packages

Data structures Services

May need to adjust: Wrap with custom objects Refine using inheritance

Buy vs. build trade-offs

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RestructuringManipulate system model to increase

code reuse or meet other design goals Maintainability, readability,

understandabilityMerge similar classesCollapse simple classes into attributesSplit complex classes into simpler onesRearrange classes & operations to

increase inheritance relationships

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OptimizationAddress performance requirements:

Algorithms to improve speed or memory usage

Reduce multiplicity to speed up queries Add redundancy for efficiency Add derived attributes to improve access

time Rearrange execution order Open up a “closed” architecture for

performance improvements

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Figure 7-2. Activities of object design (UML activity diagram).

Identifying components

Adjusting components

Specifying constraints

Collapsing classes

Specifying types &

Identifying missingattributes & operations

Specifying visibility

Specification

signatures

Optimization

Specifying exceptions

Restructuring

Realizingassociations

Revisitinginheritance

Optimizing accesspaths

Caching complexcomputations

Delaying complexcomputations

Component selection

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Object Design Terminology

Application vs. Solution Domain Objects

Types & SignaturesVisibilityContracts, constraints:

Invariants, Preconditions, Postconditions

Exceptions

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Example Object Design

Geographical Information

JEWEL Modeling System

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Figure 7-7. Object model for the GIS of JEWEL (UML class diagram).

* *

**

* *

**

* *

* *

PoliticalLayerWaterLayerRoadLayer

Highway SecondaryRoad

River Lake

State County

PolyLine Polygon

Layerlabel

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Figure 7-12. Adding operations to the object model of the JEWEL GIS to realize zooming and clipping (UML class diagram).

Layer

getOutline(bbox, detail)

LayerElement

label

Political LayerWater LayerRoad Layer

label

Highway Secondary road

River Lake

State County

LayerElement(polyline)LayerElement(polygon)

getOutline(bbox, detail)

elements*

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Figure 7-14. Additional attributes and methods for the Point class to support intelligent point selection and zooming (UML class diagram).

Pointx, y

Point(x, y)includeInLevel(level)excludeFromLevel(level)

notInDetailLevels

* *

PolyLine

addPoint(point)getPoints(bbox)

Polygon

addPoint(point)getPoints(bbox)

inDetailLevels

* *

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Figure 7-15. Adding type information to the object model of the GIS (UML class diagram). Only selected classes shown for brevity.

Layer

LayerElement+label:String

+label:String

Point

+Point(x, y:double)+includeInLevel(level:double)+excludeFromLevel(level:double)

+LayerElement(polyline:PolyLine)+getOutline(bbox:Rectangle2D,

detail:double):Enumeration

+Layer(label:String)

detail:double):Enumeration+getOutline(bbox:Rectangle2D, *

points*

elements

+x, y:double

+notInDetailLevels:Set+inDetailLevels:Set

PolyLine+label:String+PolyLine()+getPoints():Enumeration

11

*

1

polyline

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Managing Object DesignIncreased communication complexity

Result of collaboration among many people Scope of project grows

Consistency with prior information Revisit analysis & system design decisions Keep project & design goals in mind Maintain change history Ensure documents reflect current state

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Preview of Chapter 9

Testing“The software is done.

We are just trying to get it to work.”

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Opposing Goals of Testing

To ensure/demonstrate proper functioning

To “break” the system, find defects

What constitutes success/failure in each of the above approaches?

Which approach is easier? (Possible?)

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Quality Assurance TechniquesFault Avoidance

Development processes & methodologies Throughout analysis, design &

implementationFault Detection

Testing & debugging After code has been written

Fault Tolerance Recovery from failures Post-delivery, run-time activities

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Types of tests – Part 1

Unit tests Find faults in an individual object

Integration tests Find faults in a subsystem Multiple objects working together

System tests Further integration, all components

together

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Types of tests – Part 2

Functional testing Conformance to functional requirements

Performance testing Conformance to non-functional

requirementsAcceptance & installation testing

Done by client, with support by developers

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For Next Time

Chapter 9 – TestingPay special attention to

Stubs & Drivers