Components The OO way of designing software

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ComponentsThe OO way of designing software

• Stefan Negritoiu
• stefan.negritoiu_at_duke.edu
• March 26, 2001

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Outline

• Concepts
• Local scenarios
• Distributed scenarios
• The real world
• COM, DCOM, EJB, CORBA, RMI, SOAP, ROPE
• Samples and demos
• QA

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Concepts

• Object oriented abstractions
• Function
• Class
• Library
• Component
• Aspect

a language neutral, independently implemented
package of software services, delivered in an
encapsulated manner and replaceable container,
accessed via one or more published interfaces
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Concepts

• 3-tier/n-tier model

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Concepts

• Instantiation
• Client language runtime calls component subsystem
  which asks the component to create itself
• Lifetime management
• Binding
• Offered by client language runtime

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Concepts

• Method invocation
• IDL
• Marshaling
• Serialization

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Concepts

• Distributed scenario needs common
• IDL
• proxy/stub
• Transport
• marshaling

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Real-world

• DCOM (Microsoft)
• Component subsystem COM/COM
• IDL MIDL
• Transport MS RPC
• Component subsystem includes
• Security, pooling, synchronization
• MSMQ (message queuing)
• MSCS (clustering)
• MTS (transactions)

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Windows DNA Object Model, The Middleware Company,
Dec 1999
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Real-world

• CORBA (OMG)
• Component subsystem ORB
• IDL OMG IDL
• Transport IIOP
• CORBA does not define a server side component
  coordinator framework... It does not deal with
  issues such as transactions, component packaging,
  or automatic state management. The integration of
  these pieces is left as an exercise for the
  vendors

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Real-world

• EJB (Sun)
• Not a true distributed framework
• Component subsystem Java/JVM
• IDL none needed
• Transport IIOP-RMI
• Can be integrated with CORBA as an ORB
• Controversial Windows DNA vs. EJB
• Do not use this paper when trying to make a
  decision on EJB vs. MTS/COM - just don't ever
  choose Microsoft.

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The EJB Object Model, The Middleware Company, Dec
1999
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Real-world

• ? (SOAP)
• Component subsystem COM, any ORB
• IDL XML
• Transport HTTP

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Real World

• SOAP XML over HTTP

POST /string_server/Object17 HTTP/1.1 Host
209.110.197.2 Content-Type text/xml Content-Lengt
h 152 SOAPMethodName urnstrings-comIStringrev
erse ltEnvelopegt ltBodygt ltmreverse
xmlnsm'urnstrings-comIString'gt
lttheStringgtHello, Worldlt/theStringgt
lt/mreversegt lt/Bodygt lt/Envelopegt
200 OK Content-Type text/xml Content-Length
162 ltEnvelopegt ltBodygt ltmreverseResponse
xmlnsm'urnstrings-comIString'gt
ltresultgtdlroW ,olleHlt/resultgt
lt/mreverseResponsegt lt/Bodygt lt/Envelopegt
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Samples

• IE, MS Office
• Any e-commerce
• MapQuest (fictional)
• EBay?
• ICCRC
• MyDuke

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Samples - MyDuke.com
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Samples MyDuke vs. IMP
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Demos

• Writing a component
• Using a component from various programming
  languages
• SOAP example

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QA

• Resources
• Understanding COM, David Platt
• Beginning ATL COM, Richard Grimes
• Mastering EJB, Ed Roman
• http//www.omg.org/gettingstarted/readingroom.htm
• http//msdn.microsoft.com
• http//java.sun.com/products/ejb
• Duke MUG (MSDN share \\jazz\msdn)