1. COM, DCOM and Software Components
Nat Brown
COM Program Management
Microsoft Corporation

2. Agenda What are COM and DCOM? What’s right with COM
What’s wrong with CORBA / IIOP
Interesting COM Research Topics
Additional Reference Material

3. The COM Programming Model A scalable programming model
Client
Component
In the same process
Fast, direct function calls
Client
Component
COM
Client Process
Server Process
On the same machine
Fast, secure IPC
Across machines
Secure, reliable and flexible DCE-RPC based DCOM protocol
COM
DCE
RPC
Client
Server Machine
Client Machine
Component

4. DCOM Architecture Flexible and extensible
Pluggable Transports
Client Machine
Server Machine D C O M D C O M
TCP, UDP
IPX, SPX
COM
Object
Clients
HTTP
Msg-Q

5. DCOM Architecture Flexible and extensible
Pluggable Security
Client Machine
Server Machine D C O M
NT4 Security
SSL/
Certificates
NT Kerberos
DCE Security D C O M
TCP, UDP
IPX, SPX
COM
Object
Clients
HTTP
Falcon

6. DCOM Architecture Efficient 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
Client
Server
Client

7. DCOM Architecture Efficient and scalable
Low Bandwidth
Header is 28 bytes over DCE-RPC
Keep-Alive Messages bundled for all connections between Machines
Client Machine
Server Machine
Keep-Alive Traffic
for all connections
Client #1
Server
Logical “Connections”
or “Sessions”
Client #2

8. What’s 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. What’s 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. Deep/Robust Extensibility
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
What’s 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
Component
Type Info
DLL Register
RefCounting
Query Interface
Methods
Class Factory
Connection Points
IDispatch
Component
Meta Data
DLL Register
RefCounting
Query Interface
Methods
Class Factory
Connection Points
IDispatch
Clients
Network
Server
Thread Pool
Queue
Connections
Context
Security
Shared Data
Receiver
Synchronization
Service Logic
Configuration
Management
Receiver
Queue
Connections
Context
Security
Management
Configuration
Thread Pool
Service Logic
Synchronization
Shared Data
Server
MTS = easier servers
Easier components?

15. Reference Material
[Box1 97] D. Box, Q&A ActiveX/COM, Microsoft Systems Journal, March 1997, pp
[Box2 97] D. Box, Q&A ActiveX/COM, Microsoft Systems Journal, July 1997, pp
[Brockschmidt 93] K. Brockschmidt, Inside OLE 2, Redmond, Washington: Microsoft Press, 1993.
[Brown 96] N. Brown, C. Kindel, Distributed Component Object Model Protocol -- DCOM/1.0
[Chappell 96] D. Chappell, Understanding ActiveX and OLE, Redmond, Washington: Microsoft Press, 1996.
[COM 95] The Component Object Model Specification,
[DCE 95] AES/Distributed Computing - Remote Procedure Call, Revision B, Open Software Foundation,
[Rogerson 96] D. Rogerson, Inside COM, Redmond, Washington: Microsoft Press, 1996.
[Wang 97] Y. M. Wang, COM/DCOM Resources,