Vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie Object-Oriented Software...

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


Topics:

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


Introduction

If OO

is the Answer,

What isthe Question?


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


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


Managing O-O Projects

Did YOU ever manage a project?


Critical Success Factors

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


Key Failure Indicators

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

see Surviving Object-Oriented Projects: A Managers Guide


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!


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


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, ...


The hazards of C++?

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

• Java -- relative simplicity and portability


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!


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


Case studies: Application Framework

• The hush Framework• The San Francisco Framework


Technology and Trends

UML Risks

JavaFrameworks

ContractsCORBAPatternsDOT


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


UML - Quick Reference and Overview

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


Design by Contract

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

see Ch. 3, Contracts


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 ...


The benefits

The benefits of frameworks stem from the inversion of control.

A Framework defines an Architecture?


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


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


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


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


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


Kinds of Patterns

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

Command, …

see also

see UML


Java

If Java

is the Answer,

What isthe Question?

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


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 ...


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!


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 ...


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


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!


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


Dimensions of Risks

• Knowledge• Teaming• Productivity• Ownership• Distractions

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


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



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

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

• Ownership– function / component owners -- create responsibility



• 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


Conclusions

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


Yet beware of

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


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.


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

Vrije Universiteit amsterdamPostacademische Cursus Informatie Technologie Object-Oriented Software...

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