ClientServer Internet Style

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Client/Server - Internet Style

• IEM Program - EE 690
• Fall 2000November 4, 2000
• Chapter 26 - 29

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Ch 26 - The Web - Hypertext World

• Web started as file server
• Text files
• Evolution - Figure 26-1
• Rest in networking class
• You have done this stuff!
• Ch 26 has details on standards and their evolution

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Ch 27 - The Web - Interactive

• CGI and interactive - fig 27-1
• You have done this too!
• But CGI has problems
• state
• resources

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CGI Problems

• Resources Problem - Fig 27-6
• item 5 - new process every user
• many have improved with use of DLLs etc
• ASP, servlets, NSAPI, ISAPI
• State (CGI has none)
• hidden data on forms fig 27-7
• cookies stored on client

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Ch 28 - The Web - Object World

• Java - mobile code
• CORBA/Java
• Documents as objects

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Java

• Started with applets (fig 28-1)
• just in time shippable clients
• 1 or more java beans in a JAR file
• Mobile code
• self contained and executable
• runs on different platforms (OS)
• life cycle controlled
• distribution

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Byte codes

• Partially compiled
• compiled to least common denominator
• client machine completes the compilation using
  their platform specific Java compiler
• therefore, java is machine independent
• Fig 28-2

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Bytecode problems

• Slower than native compiling
• Not all Java run-time interpreters are equivalent
  (Great Microsoft criticism)

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Java Security (protection)

• Fig 28-2 - Java and verifier
• does not allow pointers to memory locations
• verifier examines code before compiling
• Has access control lists that keeps code from
  accessing files it should not have access to
• browser settings can shut off all Java stuff

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Java and CORBA as a Web Standard

• Goal - object oriented web
• CORBA - definitions and standards
• Java - implementation of CORBA
• Lots of groups involved
• OMG, W3, ..
• No CGI and no cookies! (fig 28-5)
• with CGI you must start a new instance of CGI
  engine every time - not with objects

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CGI vs. Java/CORBA

• Page 610
• feature comparisons
• page 611
• performance comparisons

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Java Foundation Classes (JFC)

• Also called Swing
• GUI elements of Java
• In past - had to transport GUI in Java package
• Java 2
• client runtime engine has JFC which have all GUI
  functions
• Sound like Microsoft DLLs??????

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Document Objects

• XML (Extensible markup Language)
• Language for creating document structures
• Lets user create new tags
• DOM (Document Object Model)
• CORBA IDL for accessing structure of XML
• XSL (Extensible Style Language)
• CSS for XML
• Separates user interface from data

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The End