Technology and Trends

UML
				Risks
			Java
		Frameworks
Contracts
	CORBA
				Patterns
			DOT

slide: The Trends and Technology Matrix

UML

The Unified Modeling Language

use case diagram
class diagram
behavior diagrams:
- statechart diagram
- activity diagram
- interaction diagrams:
  - sequence diagram
  - collaboration diagram
implementation diagrams:
- component diagram
- deployment diagram

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

slide: UML

UML - Quick Reference and Overview

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

Contracts

Design by Contract

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

see Ch. 3, Contracts

slide: Design by Contract

Frameworks

Frameworks = Components + Patterns

Ralph Johnson, CACM Nov. 1997

Self-documentation Principle

Bertrand 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 ...

slide: Frameworks = Components + Patterns

The benefits of frameworks stem from the inversion of control

A Framework defines an Architecture?

slide: The benefits ...

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

see patterns

slide: Software Architecture

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

slide: A Catalogue of Design patterns

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 - tradeoffs

to understand the costs and benefits

slide: The Pattern Schema

Causes for Redesign

design for change

creating an object by specifying a class explicitly -- Abstract Factory, Factory Method, Prototype
dependence on specific operations Chain of Responsibilty, Command
dependence on hardware & software platforms -- Abstract Factory, bridge
dependence on object implementation or representation Abstract Factory, Bridge, Memento, Proxy
algorithm dependence -- Builder, Iterator, Strategy, Template Method, Visitor
extending functionality by subclassing -- Bridge, Chain, Composite, Decorator, Observer
tight coupling -- Abstract Factpry, Bridge, Chain of Responsibilities, Command, Facade, Mediator, Observer
inability to alter classes conveniently -- Adaptor, Decorator, Visitor

slide: Causes for Redesign

Kinds of Patterns

creational patterns -- factory, singleton, ...
structural patterns -- adaptor, composite, bridge, ...
behavioral patterns -- mediator, observer, command, ...

Java

If
	Java
		is the Answer,
What is
		the Question?

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

slide: What is the Question?

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 todays languages are inadequate for Software then Java must be inadequate too ...

slide: The dream: UNCOL

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!

slide: Hostages of legacy code

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 ...

slide: Is Java doomed to repeat history?

Java = watered-down C++, retrofitting Pascal

Problems

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

slide: Java = ...

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!