7/27/2019 dcom1

1/33

(D)COM(D)COMMicrosofts responseMicrosofts response

to CORBAto CORBA

Alessandro RISSO - PS/CO

7/27/2019 dcom1

2/33

Talk OutlineTalk Outlinex DCOM

x What is DCOM ?

x COM Components

x COM Library

x Transport Protocols, Security & Platforms Availability

x Services Based on DCOM

x DCOM - Pros & Cons

x DCOM & CORBA - A Comparison

7/27/2019 dcom1

3/33

Middleware Workshop - 26 March 1999

The FoundationThe Foundation

x COM is Microsofts Component Model

x COM defines a Binary Standard for Components

Interoperability

x COM Component is a piece of compiled code that

provides some service to the rest of the system

x DCOMprovides Distributed Services to COM

x allows COM Components to transparently communicate

across the network

7/27/2019 dcom1

4/33

Middleware Workshop - 26 March 1999

Evolution of COMEvolution of COM

x 1993 - OLE2 introduced COM

x 1994 - COM in Windows NT 3.5

x 1996 - DCOM in Windows NT 4

x 1996 - ActiveX, COM enabled for the Internet

x 1996 - Microsoft Transaction Server (MTS)

x 1998 - DCOM for W95, Sun Solaris, HP-UX, IBM AIX ,

x 200x - COM+

7/27/2019 dcom1

5/33

Middleware Workshop - 26 March 1999

COM ArchitectureCOM Architecture

7/27/2019 dcom1

6/33

Middleware Workshop - 26 March 1999

COM ComponentsCOM Components

x

are language-neutralencapsulated objects

x expose a set of structured interfaces

x enable other applications or components

to communicate in astandard way

7/27/2019 dcom1

7/33

Middleware Workshop - 26 March 1999

COM ClassCOM Class

x named, concrete implementation ofone or more interfaces

x identified by a class identifier - CLSID

Slide classInterfaces

IColorManager

IShow

CLSID = {55ca6522-e33e-22cf-55da-0091e2a3a124}

void SetForegrdColor (Obj o, Color c)Color GetForegrdColor (Obj o)

.

{{

7/27/2019 dcom1

8/33

Middleware Workshop - 26 March 1999

InterfaceInterface

x a group of related functions that specifies a

contract - name, interface signature and semantics

x denotes behavior only, not state

x are immutable - never versioned

x are strongly typed - unique identifier IID

x interfaces are described in MS-IDL - derived from

the IDL of OSF/DCE

7/27/2019 dcom1

9/33

Middleware Workshop - 26 March 1999

IUnknownIUnknown InterfaceInterface

x IUnknown defines a standard for communicationwith components

x All COM components are required to implement it

x IUnknown has three methods:

x QueryInterface

x AddRef

x Release }Reference Counting Methods} Returns the Interface Pointer

7/27/2019 dcom1

10/33

Middleware Workshop - 26 March 1999

Virtual Function TablesVirtual Function Tables

7/27/2019 dcom1

11/33

IDL & COMIDL & COM

InterfacesInterfaces

written inwritten in

MS-IDLMS-IDL

Small BinariesSmall Binaries

loaded inloaded in

Client & ServerClient & Server

process spacesprocess spaces

MIDLMIDL

CompilerCompiler

Proxy & StubProxy & StubUUIDsUUIDs

for thefor the

RegistryRegistry DBDB. . . . .. . . . . TypeType LybraryLybrary

UniversallyUniversally

Unique IDs file,Unique IDs file,

with all Class IDwith all Class ID

& Interface IDs& Interface IDs

Binary Object withBinary Object with

class & interfacesclass & interfaces

metadatametadata for Tools,for Tools,

likelike VBasicVBasic & Java& Java

7/27/2019 dcom1

12/33

Middleware Workshop - 26 March 1999

COM LibraryCOM LibraryA system component that providesA system component that providesthe mechanism of COMthe mechanism of COM

x Provides the ability to make IUnknown call

across processes

x Encapsulate all work associated with the

launching of components

x Establish connections between componentsx In Win9x/WinNT is called OLE2.DLL

7/27/2019 dcom1

13/33

PublisherPublisherServerServer

ObjectObjectClientClientProgramProgram

Local

Machine

Local

Machine

The COM LibraryThe COM Library

A System Component that provides theA System Component that provides themechanism of COMmechanism of COM

ServiceService

Control MangerControl Manger

COM RuntimeCOM Runtime REGISTRY DatabaseREGISTRY Database

{CLSID}{CLSID} Server.DLLServer.DLL

Client ProcessClient Process

1

2

34

5

7/27/2019 dcom1

14/33

PublisherPublisherCOMCOM

RemoteRemote

ObjectObject

ProxyProxy

ClientClient

ProgramProgram

Local MachineLocal Machine

Accessing COM ServicesAccessing COM Services

ClientClient ProcessProcess

COMCOM Local ServerLocal Server

StubStubLocalLocal

ObjectObject

Remote ServerRemote Server ProcessProcess

RPC

Remote MachineRemote Machine

COMCOM Local ServerLocal Server

Local ServerLocal Server ProcessProcess

LPC

In-ProcessIn-Process

ServerServer COMCOM

RemoteRemoteObjectObject

ProxyProxyStubStub LocalLocal

ObjectObject

In-ProcessIn-Process

ObjectObject

7/27/2019 dcom1

15/33

Middleware Workshop - 26 March 1999

Protocols & SecurityProtocols & Security

x DCOM is based on MS-RPC

x MS implementation of OSF/DCE-RPC specification

x Tightly-Coupled & Synchronous

x DCOM can use all major Transport Protocols

x default ones are TCP & UDP

x DCOM provides a Security Framework

x Its based on WinNT Access Control Lists for componentsx ACLs indicate which users or groups of users have the right

to access a component of a certain class

7/27/2019 dcom1

16/33

Middleware Workshop - 26 March 1999

DCOM AdministrationDCOM Administration

x For distributed applications, its criticalx To be able to centralize administration

x To make client installation as straightforward as possible

x COM components administration is not easy:

x COM components only increase in size (no versioning)

x

The biggest problem for maintaining fat clients isupdating those clients to newer versions, by modifying the

Registry file of each computer using them

7/27/2019 dcom1

17/33

Middleware Workshop - 26 March 1999

DCOM Availability onDCOM Availability onnon-Microsoft Platformsnon-Microsoft Platforms

x Sun Solaris 2.5 (Sparc)

x HP-UX

x

Linux 2.0 Intelx SCO UnixWare

x Siemens Nixdorf SINIX

x Digital Unix 4.0 (Alpha)

x IBM AIX

x

Digital Open VMSx IBM MVS 5.2.2 (OS390)

x IBM OS/400

EntireX- www.softwareag.comCOMsource- www.opengroup.org/comsource

7/27/2019 dcom1

18/33

Middleware Workshop - 26 March 1999

Services Based on DCOMServices Based on DCOMx Microsoft Transaction Server

x MTS manages Transactions, System Resources &Components Life Cycle

x MTS is a Standard for Server-Side COM Components

x Microsoft Message Queue

x

MSMQ implements asynchronous communicationx MSMQ will be seen from DCOM as a new pluggable

Transport Protocol (WinNT 5)

7/27/2019 dcom1

19/33

Middleware Workshop - 26 March 1999

Domain Specific ServicesDomain Specific Servicesbased on Windows DNA, the Windowsbased on Windows DNA, the Windows

DistributedDistributed interNetinterNet Applications ArchitectureApplications Architecture

x Windows DNA is a framework for business

solutions based on COM technologies

x DCOM, MTS, MSMQ, IIS - MS Web Server, ...

x Available Industry Specifications & Products

x OLE for Process Control (OPC)

x Financial Services

x Transportation & Distribution, .

7/27/2019 dcom1

20/33

Middleware Workshop - 26 March 1999

Microsoft Transaction ServerMicrosoft Transaction Serverx DCOM only offers basic services for

distributed computingx Building powerful COM servers can be daunting

x MTS integrates DCOM with

x System Resources management

x Server Component creation, execution & deletionmanagement

x Transactions Control & Security

x MTS is a standard for server-side components

7/27/2019 dcom1

21/33

Middleware Workshop - 26 March 1999

MTS at workMTS at work

ClientClient

MTS ExecutiveMTS Executive MTS ApplicationMTS Application

StubStub

ClassClass

FactoryFactory

ClassClass

FactoryFactory

WrapperWrapper

ContextContext

WrapperWrapper

ContextContext

ObjectObject

MTSMTS

ObjectObject

ProxyProxy

MTS Surrogate ServerMTS Surrogate Server

7/27/2019 dcom1

22/33

Middleware Workshop - 26 March 1999

x Constraints on COM Componentx Be an in-process server (DLL)

x Implement a Class Factory to create objects

x Describe all of the components interfaces in a Type Library

x State-less objects only

x Available on NT platforms only

MTS ConstraintsMTS Constraints

7/27/2019 dcom1

23/33

Middleware Workshop - 26 March 1999

Microsoft MessageMicrosoft Message

Queue ServerQueue Serverx DCOM is based on MS-RPC

x Tightly-Coupled & Synchronous

x MSMQ Communication Scenarios

x Store-and-forward communication

x Concurrent execution

x Journaled communication

x

Connectionless communicationx MSMQ will be seen from DCOM as a new

pluggable Transport Protocol

7/27/2019 dcom1

24/33

Middleware Workshop - 26 March 1999

MS-Message Queue ServerMS-Message Queue Server

x MSMQ is fully integrated with otherWindows NT features such asx Microsoft Transaction Server (MTS)

x

Microsoft Internet Information Server (IIS)x Windows NT Security Environment

x MSMQ is available on Windows 9x & NT

x MSMQ is seen from DCOM as a newpluggable Transport Protocol

7/27/2019 dcom1

25/33

Middleware Workshop - 26 March 1999

DCOM -DCOM - ProsPros & Cons& Cons

x DCOM is a Mature Technology

x Defines a Binary Standard for Components Interoperability

x Broad Tools Support - VisualBasic, VC++, VJ++ & ActiveX

x Is Programming-Language-Independent

x Provides a transparent Remote Procedure Calls to both

Local or Remote Servers

x Can use all major Transport Protocols

x MTS & MSMQ well integrate the basic DCOM functionality

x Domain Specific Services are available on the market

7/27/2019 dcom1

26/33

Middleware Workshop - 26 March 1999

DCOM - Pros &DCOM - Pros & ConsConsx COM components administration is not easy:

x COM components update requires to modify the Registry file

of each computer using them

x COM components only increase in size (no versioning)

x DCOM Services are Windows-centric

x Only a few vendors are porting DCOM on

other platformsx OpenGroup

x Software AG Systems

7/27/2019 dcom1

27/33

Middleware Workshop - 26 March 1999

CORBA ArchitectureCORBA Architecture

7/27/2019 dcom1

28/33

Middleware Workshop - 26 March 1999

DCOM - CORBADCOM - CORBAWhats similar ?Whats similar ?

q

They provide:x local and remote servers for distributed

computing

x a framework with

x ORB

x Object Servicesx Common Facilities - horizontal services

x Domain Specific Facilities - vertical services

7/27/2019 dcom1

29/33

DCOM - CORBADCOM - CORBAWhats different?Whats different?

q DCOM

x Microsoft & Open Group

~130 members

x first implementation,

then specification

q CORBA

x OMG consortium

~ 800 members

x first specification,

then implementation

7/27/2019 dcom1

30/33

DCOM - CORBADCOM - CORBAWhats different?Whats different?

q DCOMx Communication based on

RPC protocol

x synchronous communication

x COM library with

more built-in functions &less services

x Built in OS

q CORBAx Communication based on

IIOP or proprietary protocol

x synch + asynchronous commun.

x ORB with

more services &less built-in functions

x Built above OS

7/27/2019 dcom1

31/33

DCOM - CORBADCOM - CORBA

Whats different?Whats different?

q

DCOMx Object consist of one or

more categories ofinterfaces

x each interface is named &has its own derivationhierarchy

x Class identified by CLSID

x Error reporting

x methods return an integervalue that indicate thesuccess or failure of the call

q

CORBAx Objects follow a standard

object model

x an interface is defined by itsclass & all the ancestors ofthat class

x Class identified by Name

x Error reporting

x Exception mechanism, whereerrors are returned as astructure embedded withinanother object

7/27/2019 dcom1

32/33

Middleware Workshop - 26 March 1999

ConclusionsConclusions

The selection process between DCOM &others Middleware solutions revolvesaround the choice of server environments

on which these systems will operate

7/27/2019 dcom1

33/33

Middleware Workshop - 26 March 1999

ReferencesReferences

x COM-DCOM-MTS & MSMQ Documentationx www.microsoft.com/com

x www.microsoft.com/msmq

x EntireXx www.softwareag.com

x COMsource

x www.opengroup.org/comsource