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COM, DCOM and Software Components

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Title: 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
8
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

9
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

11
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?

14
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?
15
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
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