vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Object-Oriented Software Engineering

Anton EliënsVrije Universiteit, Amsterdam

28 october 1998

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

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Topics:

• OO technology• The OO life cycle• Project Management• Application Frameworks• Current developments and trends

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Introduction

If OO

is the Answer,

What isthe Question?

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Keywords 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

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Characterisations of OO

1. encapsulation + inheritance2. data abstraction + polymorphism3. interfaces + components4. types + implementations5. CORBA + Application Frameworks6. Java + nothing else7. a metaphor + hype8. everything I can sell …

Let's have a look at the Introduction from Principles of Object-Oriented Software Development

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Managing O-O Projects

Did YOU ever manage a project?

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Critical 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 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 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 - 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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Drawbacks

• 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++?

• 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++

• 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 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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Case studies: Application Framework

• The hush Framework• The San Francisco Framework

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Technology and Trends

UML Risks

JavaFrameworks

ContractsCORBAPatternsDOT

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The Unified Modelling Language

• use case diagram• class diagram• behaviour diagrams:

– state-chart diagram– activity diagram– interaction diagrams:

• sequence diagram• collaboration diagram

• implementation diagrams:– component diagram– deployment diagram

For some background see: Ch. 11: Methods and Tools

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UML - Quick Reference and Overview

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

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Design 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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Frameworks

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

• Self-documentation PrincipleBertrand Meyer, OO Software Construction

2nd ed.

the designer of a module should strive to make all information about the module part of the module itself ...

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The benefits

The benefits of frameworks stem from the inversion of control.

A Framework defines an Architecture?

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Software 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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A 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: 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)

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

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

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 Patterns

• creational patterns -- Factory, Singleton, ...• structural patterns -- Adaptor, Composite, Bridge, ...• behavioral patterns -- Mediator, Observer,

Command, …

see also

see UML

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Java

If Java

is the Answer,

What isthe Question?

see Ted Lewis, IEEE Computer, March 1997, p. 136

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The dream: UNCOL

• Java is pervasive• remember, most of Java is just warmed-up C/C+

+• UNCOL = Universal Common Language

(1963) Algol -> PL/I -> Pascal -> Ada -> C++ -> …• Java as UNCOL: the dial-tone of the Internet

if today's languages are inadequate for Software then Java must be inadequate too ...

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Hostages of legacy code

• our responsibility is that future applications (built with Java) are well-behaved legacy systems

• US DOD: $ 30 billion in year 2000 problem• maintaining legacy COBOL from the 70's is a

major industry ...• by 2010, Java will be the maintenance tail

wagging the software dog!

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Is Java doomed to repeat history?

• elegant minimalism is one of the goals of Java,remember Pascal, a toy language!

• Java lacks IO, OS support ...

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Problems

• Java = watered-down C++, retrofitting Pascal– syntax: int i = ++i--;– unruly scope rules: C++ plus f i n a l, n a t i v e, s y n

c h r o n i z e d, ...– threads: potential deadlocks

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Java: a better mousetrap?

• requirements: no support (assert)• defacts: syntax, non-standard APIs• components: Beans ActiveX, CORBA,

OpenDoc• cycle time: Java does little to accommodate

Internet time, like script languages do• complexity: Java does not advance the

intellectual frontier!

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CORBA

• 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 andsee frameworks

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Dimensions of Risks

• Knowledge• Teaming• Productivity• Ownership• Distractions

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

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Risk Reduction Strategies

• Knowledge– clear the fog -- get to the real issues– early and regular delivery -- discover what you don't

know– prototype! -- discover how it really works– create microcosm -- do something real, but with care

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Risk Reduction Strategies

• Teaming– holistic diversity -- co-ordinate specialists!

• Productivity– gold rush -- start immediately, adjust slowly

• Ownership– function / component owners -- create responsibility

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Risk Reduction Strategies

• Distractions– someone always makes progress -- no total

interruption– team per task -- a subteam deals with diversions– sacrifice one person -- and preserve the team

• Training– day care -- hire an expert to take care of novices

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Conclusions

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

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

Yet beware of

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

vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie

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 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