vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Object-Oriented Software Engineering

Object-Oriented Software Engineering

Anton Eliëns

Vrije Universiteit, Amsterdam

27 april 1999

http://www.cs.vu.nl/~eliens/cmg/html/oo

http://www.cs.vu.nl/~eliens/online/courses/cmg/oo

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Topics:Topics:

• Basic OO technology• Application Framework(s)• Universal Modeling Language• Design Patterns• Project Management• Current developments and trends

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IntroductionIntroduction

If

OO

is the Answer,

What is

the Question?

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Keywords and phrasesKeywords and phrases

• the OO lifecycle -- modelling• encapsulation, inheritance, delegation,

polymorphism• specification and implementation inheritance• design by contract• interfaces, components and frameworks• idioms, patterns, software architecture

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Basic OO TechnolologyBasic OO Technolology

Technology determines the effectiveness of the approach

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ConceptsConcepts

• Encapsulation• Data hiding• Inheritance• Polymorphism

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EncapsulationEncapsulation

• An object contains data and methods• It provides a boundary:• to the world outside• to its ‘children’

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Information hidingInformation hiding

• Reduces complexity• Allows you to defer implementations• Remember: Ignorance is bliss• Helps in decoupling components

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InheritanceInheritance

• A mechanism for code-sharing• Supports incremental development• Organize by classification• Allows for abstract interfaces

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PolymorphismPolymorphism

• An object may have multiple types• An abstract type: when it is used• A concrete type: when it is created• An object’s type is determined by its behavior• An object’s type is determined by the messages

it allows

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vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Design by ContractDesign by Contract

• formal basis -- pre and post conditions• refinement -- by inheritance or polymorphism• runtime checks -- division of responsibility

see Ch. 3, Contracts

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The San Francisco Framework

The San Francisco Framework

How useful is an OO framework?

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•Example - San Francisco Framework

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A framework is ...A framework is ...

• a collection of components• a generic solution for a class of problems• a frame of mind for solving problems• a set of architectural constraints

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The San Francisco FrameworkThe San Francisco Framework

• is meant to develop business applications• is based on Java technology• may solve 70% of your problem• leaves 30% (minimum) to solve for you• may set a standard• or may fail to do so ...

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San Francisco - motivationSan Francisco - motivation

• The project was started when several software vendors asked IBM to help modernizing their application products

• However, there were several barriers preventing them from being able to update their applications

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Barriers to modernizingBarriers to modernizing

• (1) The problem of how to retrain their development staff to effectively use OO technology.

• (2) The risk involved in moving to a new technology.

• (3) moving -> the cost of the change• The software developers realized they needed

some basic infrastructure.• Many companies could not develop this

infrastructure themselves.

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San Francisco - the pressSan Francisco - the press

• The San Francisco project helps to solve these problems by offering developers Business Process Components,

• designed as frameworks that provides an object oriented infrastructure,

• a consistent application programming model, and

• some default business logic• The frameworks make it easier to move to OO

technology because developers use well-tested services instead of building their own.

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vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

San Francisco Framework - layersSan Francisco Framework - layers

• Core Business Process Layer - the highest• Common Business Objects Layer - middle• Foundation Layer - lowest

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Core Business ProcessesCore Business Processes

• The objective for this layer is to create a sound architecture and highly extensible OO implementation for the basic structure and behavior which any application provider delivering a solution in the application doamin would require:

• Accounts Receivable/Payable Ledger• General Ledger Framework• Sales Order Management Framework• Purchase Order Management

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vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Common Business ObjectsCommon Business Objects

• Business Objects common to multiple domains• Common Application level Services• CBO:• Business Partner• Address• Number - decimal structure• Currency - how many euros in a dollar?

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Foundation LayerFoundation Layer

• Foundation Object Model Classes• Utilities

• in other words: it provides the infrastructure• comment: reinventing the wheel is not a big

problem, because the wheel is a terrific invention

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Foundation Object Model ClassesFoundation Object Model Classes

• Command• Entity• Dependent• Collection/Iterator• Factory

• you need to study Design Patterns to appreciate these ...

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Using the San Francisco FrameworkUsing the San Francisco Framework

• … The San Francisco Frameworks are designed to make many types of extensions easy for application dvelopers:

• overriding the default business logic in supplied methods

• adding additional attributes to existing classes• adding additional methods to existing classes

• from the report: Complete documentation will be provided …

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ExampleExample

• Two classes: Receipt and Purchase order Line• default attributes, methods• default business logic: inspect Quality on receipt• Extension: enhance this logic• subclass Receipt • override inspection method• change logic to include checks against supplier

tables, and hazardous or high value products

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vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

San Francisco - issuesSan Francisco - issues

• Standards: OMG/CORBA Business Issues• Technology Integration:• Compound Documents: Lotus Notes,

JavaBeans, Active X• Business process Modelling and Control:

workflow engines may be used as glue …• Internet/Intranet and Java: applications may be

designed ….• Conclusions: … a bit premature ...

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Universal Modeling LanguageUniversal Modeling Language

• … why you need models?• Models are necessary to communicate,• to stabilize abstractions• as a reference for the implementation• and maintenance• and you need an agreement on the notation and

formalisms in which you express your models

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Unified Modeling LanguageUnified Modeling Language

• class diagrams -- conceptual structure • use cases -- functional requirements • interaction diagrams -- operational aspects • package and deployment -- implementation • state and activity -- dynamic behavior

• See http://www.rational.com/uml and UML Distilled, [Fowler97].

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UML - Quick Reference and OverviewUML - Quick Reference and Overview

adapted from the Rational Rose Quick Reference at http://www.rational.com/uml/qr

and Principles of O-O Software Development

Appendix UML

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Class diagramsClass diagrams

• Describe properties of classes• and their (inter) relations

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Interaction diagramInteraction diagram

• To gain an operational intuition• to check calling chains

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Use casesUse cases

• Define the boundary between the system and its uses

• Might be a good subject for a paper ...

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vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Collaboration diagramsCollaboration diagrams

• To further analyze the relations between classes• augments: class diagram and interaction

diagram

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Visibility propertiesVisibility properties

• More implementation oriented• But remember: ignorance is bliss ...

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Component and Deployment diagramComponent and Deployment diagram

• Primarily for the system architect

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vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Associations, roles, aggregationsAssociations, roles, aggregations

• You may augment the model to any extent• Personally, I believe in constraints

• See for example: Fowler - Analysis Patterns

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vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

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Dynamic object behavior - state transitionsDynamic object behavior - state transitions

• State transition diagrams are rarely used• except in applications that require scheduling:• workflow, simulation, concurrency

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vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

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ExamplesExamples

- interactive drawing tool

- the reactor pattern (events)

- business process modeling

- the observer pattern

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Interactive drawing toolInteractive drawing tool

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Reactor (event-handling) patternReactor (event-handling) pattern

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Reactor - Interaction diagram (events)Reactor - Interaction diagram (events)

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Business process modelingBusiness process modeling

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(simulation) event state transition diagram(simulation) event state transition diagram

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Observer PatternObserver Pattern

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A Catalogue of Design patternsA Catalogue of Design patterns

• a common design vocabulary• documentation and learning aid• an adjunct to existing methods• a target for redesign

see the GOF Design Patterns and the Patterns Homepage

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The Pattern Schema: structureThe Pattern Schema: structure

• Name - handle– increases design vocabulary

• Problem - when to apply– explains the problem and the conflict

• Solution - general arrangement– design, responsibilities, collaborations

• Consequences - trade-off's– to understand the costs and benefit

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Causes for Redesign (1)Causes for Redesign (1)

1. creating an object by specifying a class explicitly -- Abstract Factory, Factory Method, Prototype

2. dependence on specific operations -- Chain of Responsibility, Command

3. dependence on hardware & software platforms -- Abstract Factory, Bridge

4. dependence on object implementation or representation -- Abstract Factory, Bridge, Memento, Proxy

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Causes for Redesign (2)Causes for Redesign (2)

5. algorithm dependence -- Builder, Iterator, Strategy, Template Method, Visitor

6. extending functionality by subclassing -- Bridge, Chain, Composite, Decorator, Observer

7. tight coupling -- Abstract Factory, Bridge, Chain of Responsibilities, Command, Facade, Mediator, Observer

8. inability to alter classes conveniently -- Adaptor, Decorator, Visitor

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Kinds of PatternsKinds of Patterns

• creational patterns -- Factory, Singleton, ...

• structural patterns -- Adaptor, Composite, Bridge, ...

• behavioral patterns -- Mediator, Observer, Command, …

see UML

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Managing O-O ProjectsManaging O-O Projects

Did

YOU

ever

manage

a

project?

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Critical Success FactorsCritical Success Factors

• use incremental scheduling and staging• find and fix failing ideas• develop a habit of delivering• get: sponsor, project manager, technical leader

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Key Failure IndicatorsKey Failure Indicators

• absence of incremental development• use of C++ in commercial IS

see Surviving Object-Oriented Projects: A Managers Guide

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OO - Success and FailureOO - Success and Failure

• OO = technology + mind-set• it might be new technology to your organisation• developers love it!• requires and enables communication between groups

• adopting OO may succeed or fail!

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Possible benefits - responsivenessPossible benefits - responsiveness

• responsiveness - variations on a theme• responsiveness to change!• time-to-market• communication - developers, users, executives• maintenance, reuse, productivity• GUI development• morale -- cutting-edge technology

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DrawbacksDrawbacks

• Are YOU underestimating?• productivity takes time• hazards of C++ (and Java, ...)• reuse is difficult• establishing a software process• business-modelling or software design?• CASE helps?• You will pay for: training, experience, tools,

consultants, ...

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The hazards of C++?The hazards of C++?

• C++ won the language war over Eiffel, Objective-C, SOM, C@+, and Java?

• Java -- relative simplicity and portability

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Managing (the complexity of) C++Managing (the complexity of) C++

• misconception: C++ is like C• consider using another language• Why does C++ exist? - engineering and

systems programming• create a subset of the language• design and coding standards• use people with knowledge!

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Risk-reduction StrategiesRisk-reduction Strategies

• look carefully all around the project• detect the risks!• list the risks in order• work on the risks in order of danger

see Risk Avoidance Patterns

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Technology and TrendsTechnology and Trends

UML

Risks

Java

Frameworks

Contracts

CORBA

Patterns

DOT

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FrameworksFrameworks

• Frameworks = Components + PatternsRalph Johnson, CACM Nov. 1997

The benefits of frameworks stem from the inversion of control.

A Framework defines an Architecture?

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Software ArchitectureSoftware Architecture

Software Architecture = a set of rules, guidelines, interfaces, and conventions used to define how components and applications communicate and interoperate with each other ...

see patterns

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CORBACORBA

• the issue is standardisation• by means of interfaces• looking for consensus• this differs from a de-facto standard• imposed by market share ...

see Ch 11: Application integration -- standards

see frameworks

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Java - perspectivesJava - perspectives

• Internet applications• Software Engineering• Language Design• System Development• Computer Science• IT (in) Business• Global Village

Informatie, januari 99: Java - een kwestie van vraag en aanbod

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Dimensions of RisksDimensions of Risks

• Knowledge• Teaming• Productivity• Ownership• Distractions

Don't discuss risks, unless you know how to do Project Management

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ConclusionsConclusions

• OO offers– a valid metaphor for SE– powerful technology– maturing design methods and notations– a rich set of patterns

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Yet beware ofYet beware of

• the learning curve• simplified hype• cutting edge technology• (over) ambitious projects

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Assignments:Assignments:

• Write a paper about one of the following topics. The paper may discuss concepts or focus on a case study.– The Unified Modelling Language -- UML– Frameworks -- for example San Francisco

• Write a comparative study of object-oriented analysis and design methods, focussing on aspects of project management.

• Describe a case study concerning the deployment of design patterns.

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Course materialCourse material

• Chapter 1• Additional material

– Ch 3: Design by Contract

– Ch 11: Methods and Tools

– Object Tutorials

• Resources– http://www.rational.com -- Rational Rose, UML– http://www.ibm.com/java/sanfrancisco -- IBM Java San Francisco

Framework

• Papers and Reports– http://www.rational.com/uml/html/summary -- UML Summary– http://www.ibm.com/Java/Sanfrancisco/prd_summary.html -- San

Francisco Technical Summary