COMDCOM An Object Oriented Middleware

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COM/DCOM - An Object Oriented Middleware

• What we are going to cover today
• What is COM/DCOM - Aditi
• COM/DCOM Architecture - Aditi
• Design Issues - Aditi
• Creating and Accessing objects - Charul
• Interface Referencing - Charul
• Data sharing (marshalling and unmarshalling) -
  Charul
• Aggregation and Containment - Charul
• Interoperation - Yufu
• Integration - Yufu
• Features - Yufu
• SOAP (Future distributed system protocol) - Yufu
• Open Questions Yufu

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What is COM/DCOM

• Microsoft first developed COM in 1993.
• An Object-Oriented Middleware
• COM (component object model) is a specification
  for writing reusable software that runs in
  component based systems.
• COM is a model based on binary reuse - This means
  that software components adhering to COM can be
  reused without any dependencies on source code.
• COM is based on object oriented programming -
  This means that COM is a story about clients
  communicating with objects. COM exploits the OOP
  paradigm to achieve higher levels of reuse than
  is possible with other models of binary reuse.

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What is COM/DCOM (continued)

• COM is interprocess-capable - This means that
  clients can create objects in separate processes
  and on remote computers.
• COM is founded on the idea of interface based
  programming - Interfaces are the key to seamless
  object distribution. Interfaces are also the key
  to COMs ability to send remote method calls
  across host boundaries.
• - GUID
• - IUnknown
• DCOM (distributed component object model) is an
  extension of COM- DCOM takes care of establishing
  an efficient communication between client and
  object even when the client code and the object
  code are actually running in different processes
  on different machines.

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COM/DCOM Architecture

• COM components in the same process- Calls between
  COM components in the same process are only a
  handful of processor instructions slower than a
  standard direct function call and no slower than
  a compile-time bound C object invocation.

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COM/DCOM Architecture (continued)

• COM components in different processes- COM
  provides this communication in a completely
  transparent fashion it intercepts calls from the
  client and forwards them to the component in
  another process.

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COM/DCOM Architecture (continued)

• DCOM COM components on different machines- The
  COM run-time provides object-oriented services to
  clients and components and uses RPC and the
  security provider to generate standard network
  packets that conform to the DCOM wire-protocol
  standard.

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Design issues- Addressed by DCOM

• Distribution
• - Location Independence
• Scalability
• - Thread Pool
• Heterogeneity
• - Language neutrality, Platform Neutrality,
  Protocol Neutrality
• Connection Management
• - Reference count

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Design issues- Addressed by DCOM (continued)

• Performance
• - Vtable
• Security
• - Access control lists
• Load Balancing
• - Referral Component
• Fault Tolerance
• - Referral Component, Hot Backup