COM, DCOM and Software Components

1
COM, DCOMandSoftware Components

• Nat Brown
• COM Program Management
• Microsoft Corporation
• natbro_at_microsoft.com

2
Agenda

• What are COM and DCOM?
• Whats right with COM
• Whats wrong with CORBA / IIOP
• Interesting COM Research Topics
• Additional Reference Material

3
The COM Programming ModelA scalable programming
model
4
DCOM ArchitectureFlexible and extensible

• Pluggable Transports

Client Machine
Server Machine
D C O M
D C O M
COM Object
Clients
5
DCOM ArchitectureFlexible and extensible

• Pluggable Security

Server Machine
Client Machine
D C O M
D C O M
COM Object
Clients
6
DCOM ArchitectureEfficient and scalable

• Multiplexing - Single Port per-protocol, per
  server process, regardless of of objects
• Scalable - Connection-Less Protocols like UDP
  Preferred
• Established Connection-Oriented (TCP) Sessions
  Reused by same client

Server
Client
Client
7
DCOM ArchitectureEfficient and scalable

• Low Bandwidth
• Header is 28 bytes over DCE-RPC
• Keep-Alive Messages bundled for all connections
  between Machines

Server Machine
Client Machine
Keep-Alive Traffic for all connections
Client 1
Server
Logical Connections or Sessions
Client 2
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Whats Right with COM

• Focus is on binary object standard and
  scalable/fine-grained component re-use
• Concreteness and depth of definition, for example
  security, lifetime management, activation,
  installation deployment
• Architected extensibility

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Whats Wrong with CORBA/IIOP

• Focus is on cross-node or network
  reuse/integration
• in practice useful for vertical solutions, not
  horizontal reuse/integration
• Incomplete specification
• marshaling format of certain types of
  data-structures
• implications of lack of services (e.g. Naming,
  Events, Lifetime management)
• No architected extensibility

10
COM Research Areas

• High-Level Language Integration
• Application Management
• Ease-of-use
• Deep/Robust Extensibility

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Language Integration

• Re-Use Mechanisms
• Inheritance, Containment, Delegation, Aggregation
• Interception
• Constructs of modern OO languages
• classes, fields, exceptions
• Constructs of modern 4GL/RAD tools
• data-binding
• auto-persistence, -everything
• Meta Data

12
Application Management

• Distribution of Code Data Configuration
  Information
• Security and Security Delegation
• Security roles and re-use of components
• Performance Monitoring
• Runtime Environment

13
Ease-of-Use

• Whats the next programming model layer to vastly
  improve ease-of-use?
• Transactions?
• Auto-caches state management?
• Auto-distribution -execution?

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Ease-of-Use First Steps
Clients
Network
Receiver
Queue
Connections
Context
Security
Management
Configuration
Thread Pool
Service Logic
Synchronization
Shared Data
Server
MTS easier servers
Easier components?
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Reference Material

• Box1 97D. Box, QA ActiveX/COM, Microsoft
  Systems Journal, March 1997, pp. 93-105.
• Box2 97D. Box, QA ActiveX/COM, Microsoft
  Systems Journal, July 1997, pp. 93-108.
• Brockschmidt 93K. Brockschmidt, Inside OLE 2,
  Redmond, Washington Microsoft Press, 1993.
• Brown 96N. Brown, C. Kindel, Distributed
  Component Object Model Protocol --
  DCOM/1.0http//ds1.internic.net/internet-drafts/d
  raft-brown-dcom-v1-spec-01.txt
• Chappell 96D. Chappell, Understanding ActiveX
  and OLE, Redmond, Washington Microsoft Press,
  1996.
• COM 95 The Component Object Model
  Specification, http//www.microsoft.com/oledev/ole
  com/title.htm
• DCE 95AES/Distributed Computing - Remote
  Procedure Call, Revision B, Open Software
  Foundation, http//www.osf.org/mall/dce/free_dce.h
  tm
• Rogerson 96D. Rogerson, Inside COM, Redmond,
  Washington Microsoft Press, 1996.
• Wang 97Y. M. Wang, COM/DCOM Resources,
  http//www.research.att.com/ymwang/resources/reso
  urces.htm