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
Postacademische Cursus Informatie Technologie
vrije Universiteit
amsterdam
Topics:
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Basic OO technology
Application Framework(s)
Universal Modeling Language
Design Patterns
Project Management
Current developments and trends
Postacademische Cursus Informatie Technologie
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Introduction
If
OO
is the Answer,
What is
the Question?
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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
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Basic OO Technolology
Technology determines the
effectiveness of the approach
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Concepts
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Encapsulation
Data hiding
Inheritance
Polymorphism
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Encapsulation
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An object contains data and methods
It provides a boundary:
to the world outside
to its ‘children’
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Information hiding
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Reduces complexity
Allows you to defer implementations
Remember: Ignorance is bliss
Helps in decoupling components
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Inheritance
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A mechanism for code-sharing
Supports incremental development
Organize by classification
Allows for abstract interfaces
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Polymorphism
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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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Postacademische Cursus Informatie Technologie
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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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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 ...
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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 Framework
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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 - 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 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 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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Postacademische Cursus Informatie Technologie
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San Francisco Framework - layers
• Core Business Process Layer - the highest
• Common Business Objects Layer - middle
• Foundation Layer - lowest
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Core 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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Postacademische Cursus Informatie Technologie
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Common Business Objects
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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 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 Classes
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Command
Entity
Dependent
Collection/Iterator
Factory
• you need to study Design Patterns to appreciate
these ...
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Using 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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Example
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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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Postacademische Cursus Informatie Technologie
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San 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 Language
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… 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 Language
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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 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 diagrams
• Describe properties of classes
• and their (inter) relations
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Interaction diagram
• To gain an operational intuition
• to check calling chains
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Postacademische Cursus Informatie Technologie
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Use cases
• Define the boundary between the system and its
uses
• Might be a good subject for a paper ...
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Postacademische Cursus Informatie Technologie
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Collaboration diagrams
• To further analyze the relations between classes
• augments: class diagram and interaction
diagram
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Visibility properties
• More implementation oriented
• But remember: ignorance is bliss ...
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Component and Deployment diagram
• Primarily for the system architect
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Associations, 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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Dynamic object behavior - state transitions
• State transition diagrams are rarely used
• except in applications that require scheduling:
• workflow, simulation, concurrency
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Postacademische Cursus Informatie Technologie
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Examples
- interactive drawing tool
- the reactor pattern (events)
- business process modeling
- the observer pattern
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Interactive drawing tool
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Reactor (event-handling) pattern
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Reactor - Interaction diagram (events)
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Business process modeling
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(simulation) event state transition diagram
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Observer Pattern
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A Catalogue of Design patterns
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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
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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 UML
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Managing O-O Projects
Did
YOU
ever
manage
a
project?
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Critical Success Factors
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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
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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
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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
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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
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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 Trends
UML
Risks
Java
Frameworks
Contracts
CORBA
Patterns
DOT
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Frameworks
• Frameworks = Components + Patterns
Ralph Johnson, CACM Nov. 1997
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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CORBA
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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 - perspectives
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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 Risks
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Knowledge
Teaming
Productivity
Ownership
Distractions
Don't discuss risks, unless you know how to do Project
Management
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Conclusions
• OO offers
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a valid metaphor for SE
powerful technology
maturing design methods and notations
a rich set of patterns
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Yet beware of
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the learning curve
simplified hype
cutting edge technology
(over) ambitious projects
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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
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