Visual Basic and COM+ by example

486 Pages·7.094 MB·English

by  Pieshu Li

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VViissuuaall BBaassiicc aanndd
CCOOMM++
PPrrooggrraammmmiinngg
B Y E X A M P L E
201 West 103rd Street
Peishu Li
Indianapolis, Indiana 46290
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Visual Basic and COM+ Programming Acquisitions Editor
Gretchen Ganser
by Example
Development Editor
Copyright 2001 by Que Sean Dixon
Managing Editor
All rights reserved. No part of this book shall be reproduced,
Tom Hayes
stored in a retrieval system, or transmitted by any means, elec-
tronic, mechanical, photocopying, recording, or otherwise, with- Project Editor
out written permission from the publisher. No patent liability is Heather McNeill
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ration of this book, the publisher and author assume no respon-
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sibility for errors or omissions. Nor is any liability assumed for
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herein. Proofreader
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International Standard Book Number: 0-7897-2458-8
Technical Editors
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First Printing: November, 2000
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Trademarks
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Contents at a Glance
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Part I Welcome to COM+ 5
1 What COM+ Is All About . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
2 Windows DNA2000 and COM+ . . . . . . . . . . . . . . . . . . . . . . . . . . .31
3 Introduction to Microsoft Message Queuing Services (MSMQ) . . .71
4 Introduction to Visual Basic COM Programming . . . . . . . . . . . . .111
5 Using the Component Services MMC Snap-In . . . . . . . . . . . . . . .147
Part II Developing COM+ Application Components 171
6 Writing Transactional Components . . . . . . . . . . . . . . . . . . . . . . .173
7 Compensating Resource Manager (CRM) . . . . . . . . . . . . . . . . . . .215
8 COM+ Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .257
9 Queued Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .281
10 COM+ Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .317
11 Administering COM+ Applications Programmatically . . . . . . . . .349
12 More on COM+ Programming . . . . . . . . . . . . . . . . . . . . . . . . . . .387
Part III Building Real-World COM+ Services Applications 409
13 Northwind Traders Online: ACOM+ Enabled
Windows DNA2000 Application . . . . . . . . . . . . . . . . . . . . . . . . . .411
14 ACase Study: COM+ and Enterprise Application
Integration (EAI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .443
Appendix A: COM+ and Related Web Resources . . . . . . . . . . . . . . . .467
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .470
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Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
About This Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Who Should Use This Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
This Book’s Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
Part I Welcome to COM+ 5
1 What COM+ Is All About . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
COM: The Component Object Model . . . . . . . . . . . . . . . . . . . . . . . .8
What Is COM? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
COM Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
The Virtual Function Table (vtable) . . . . . . . . . . . . . . . . . . . .13
COM Threading Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Distributed COM (DCOM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
In-Process Servers Versus Out-of-Process Servers . . . . . . . . .18
DCOM Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
Microsoft Transaction Server (MTS) . . . . . . . . . . . . . . . . . . . . . . .20
MTS Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
MTS Programming Model . . . . . . . . . . . . . . . . . . . . . . . . . . .21
MTS Security Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
MTS Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
What Is COM+? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Core COM+ Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
New COM+ Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
COM+ Programming Model . . . . . . . . . . . . . . . . . . . . . . . . . .27
2 Windows DNA2000 and COM+ . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Windows DNA2000 Architecture . . . . . . . . . . . . . . . . . . . . . . . . . .32
Internet Applications and Their Challenges . . . . . . . . . . . . .32
Three-Tiered Application Architecture . . . . . . . . . . . . . . . . . .33
Infrastructure Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
Where COM+ Fits In . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
Microsoft Data Access Components (MDAC) . . . . . . . . . . . . . . . . .44
MDAC and Universal Data Access (UDA) . . . . . . . . . . . . . . .44
Internet Information Services (IIS) and Active Server
Pages (ASP) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64
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3 Introduction to Microsoft Message Queuing Services (MSMQ) . . .71
Limitations of the Synchronous Processing Model . . . . . . . . . . . . .72
Message Queuing and MSMQ . . . . . . . . . . . . . . . . . . . . . . . . . . . .73
Asynchronous Processing and Message Queuing . . . . . . . . . .73
MSMQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74
MSMQ Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75
Domain Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75
Workgroup Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . .75
Queues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76
Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80
Journaling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81
Programming MSMQ in Visual Basic . . . . . . . . . . . . . . . . . . . . . . .81
MSMQ COM Object Model . . . . . . . . . . . . . . . . . . . . . . . . . . .81
Basic MSMQ Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82
Advanced MSMQ Techniques . . . . . . . . . . . . . . . . . . . . . . . . .90
An Asynchronous Ordering Application . . . . . . . . . . . . . . . . .99
4 Introduction to Visual Basic COM Programming . . . . . . . . . . . . .111
Visual Basic COM Programming Primer . . . . . . . . . . . . . . . . . . .112
Types of COM Components . . . . . . . . . . . . . . . . . . . . . . . . .112
AVisual Basic COM DLLProject . . . . . . . . . . . . . . . . . . . . .113
Writing a Simple COM Component . . . . . . . . . . . . . . . . . . .118
Building Visual Basic ActiveX DLLs . . . . . . . . . . . . . . . . . . . . . .120
Interfaces Revisited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120
Properties, Methods, and Events . . . . . . . . . . . . . . . . . . . . .127
Error Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131
Debugging and Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . .134
Designing COM Components . . . . . . . . . . . . . . . . . . . . . . . . . . . .136
Special Design Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . .142
Granularity of Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . .142
Stateful Versus Stateless . . . . . . . . . . . . . . . . . . . . . . . . . . .142
Passing Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143
Scripting Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143
Designing Windows DNAComponents . . . . . . . . . . . . . . . . .143
COM+ Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .144
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5 Using the Component Services MMC Snap-In . . . . . . . . . . . . . . .147
Introduction to COM+ Applications . . . . . . . . . . . . . . . . . . . . . . .148
Types of COM+ Applications . . . . . . . . . . . . . . . . . . . . . . . .148
ACloser Look at a COM+ Application . . . . . . . . . . . . . . . . .149
Developing a COM+ Application . . . . . . . . . . . . . . . . . . . . .150
Creating a COM+ Application . . . . . . . . . . . . . . . . . . . . . . . . . . .151
Creating a New COM+ Application . . . . . . . . . . . . . . . . . . .151
Installing New Components . . . . . . . . . . . . . . . . . . . . . . . . .154
Deleting Components from a COM+ Application . . . . . . . . .156
Importing Existing Components . . . . . . . . . . . . . . . . . . . . .157
Removing COM+ Applications . . . . . . . . . . . . . . . . . . . . . . . . . . .158
Configuring COM+ Applications . . . . . . . . . . . . . . . . . . . . . . . . . .158
Configuring Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . .159
Configuring Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .161
Configuring JIT Activation . . . . . . . . . . . . . . . . . . . . . . . . . .164
Configuring Queuing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166
Configuring Other COM+ Attributes . . . . . . . . . . . . . . . . . .168
Deploying COM+ Applications . . . . . . . . . . . . . . . . . . . . . . . . . . .168
Converting MTS Packages into COM+ Applications . . . . . . . . . .169
Part II Developing COM+ Application Components 171
6 Writing Transactional Components . . . . . . . . . . . . . . . . . . . . . . .173
Introduction to Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . . .174
Transaction Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174
ACID Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174
Transaction Managers (TMs) . . . . . . . . . . . . . . . . . . . . . . . .175
Distributed Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .176
Two-Phase Commit Protocol . . . . . . . . . . . . . . . . . . . . . . . . .177
Microsoft Distributed Transaction Coordinator (MS DTC) .177
COM+ Automatic Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . .177
Transactional Components . . . . . . . . . . . . . . . . . . . . . . . . . .178
Determining the Transaction Output . . . . . . . . . . . . . . . . . .178
ASample Transaction Application . . . . . . . . . . . . . . . . . . . . . . . .179
Application Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .179
The Workflow of Placing an Order . . . . . . . . . . . . . . . . . . . .181
Application Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . .181
Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .185
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Taking the Application for a Test Drive . . . . . . . . . . . . . . . .210
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .212
7 Compensating Resource Manager (CRM) . . . . . . . . . . . . . . . . . . .215
Resource Dispensers Versus Resource Managers . . . . . . . . . . . . .216
The Compensating Resource Manager (CRM) . . . . . . . . . . . . . . .216
Limitation of the MTS SDK . . . . . . . . . . . . . . . . . . . . . . . . .216
What Is the CRM? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .217
The CRM Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . .217
Developing a CRM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .218
ASample CRM Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222
Using Microsoft Access Resources . . . . . . . . . . . . . . . . . . . .223
The Northwind CRM Sample Application . . . . . . . . . . . . . .227
CRM Development Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .252
Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .252
Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .253
Idempotence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .253
Other Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .253
8 COM+ Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .257
COM+ Security Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . .258
Role-Based Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .259
Designing Roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .259
Using Roles to Authorize Clients . . . . . . . . . . . . . . . . . . . . .260
Authorization Versus Authentication . . . . . . . . . . . . . . . . . . . . . .273
Impersonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .274
Impersonating Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . . .275
Cloaking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .275
Security in Three-Tiered Applications . . . . . . . . . . . . . . . . . . . . .276
Security at the Middle Tier . . . . . . . . . . . . . . . . . . . . . . . . .276
Security at the Database . . . . . . . . . . . . . . . . . . . . . . . . . . .276
Mixed Security Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . .277
Other Security Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . .277
Audit Trails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .277
Security for Library Applications . . . . . . . . . . . . . . . . . . . . .278
Security for Queued Components (QC) . . . . . . . . . . . . . . . .278
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9 Queued Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .281
Introduction to Queued Components . . . . . . . . . . . . . . . . . . . . . .282
DCOM Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282
What About MSMQ? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282
Queued Components Architecture . . . . . . . . . . . . . . . . . . . .283
The Benefits of Queued Components . . . . . . . . . . . . . . . . . .284
Queued Components and Transactions . . . . . . . . . . . . . . . .285
Poison Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .287
Developing Queued Components . . . . . . . . . . . . . . . . . . . . . . . . .288
Queued Components Development Constraints . . . . . . . . . .288
Building a Simple Queued Component . . . . . . . . . . . . . . . .289
Configuring a Queued Component . . . . . . . . . . . . . . . . . . . .290
Activating a Queued Component . . . . . . . . . . . . . . . . . . . . .293
Building a Client to Test the Queued Component . . . . . . . .295
Other Considerations About Queued Components . . . . . . . .299
Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .300
Server-Side Error Handling . . . . . . . . . . . . . . . . . . . . . . . . .301
Client-Side Error Handling . . . . . . . . . . . . . . . . . . . . . . . . .302
The Exception Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .302
Queued Components Security . . . . . . . . . . . . . . . . . . . . . . . . . . .304
Making the Northwind Ordering Application Queueable . . . . . . .304
The System Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . .305
The Shipping Database . . . . . . . . . . . . . . . . . . . . . . . . . . . .306
The Queued Components . . . . . . . . . . . . . . . . . . . . . . . . . . .308
Creating and Configuring the Queueable COM+
Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .309
Modifying Order2 Components . . . . . . . . . . . . . . . . . . . . . .310
Taking the Application for a Test Drive . . . . . . . . . . . . . . . .314
10 COM+ Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .317
Introduction to COM+ Events . . . . . . . . . . . . . . . . . . . . . . . . . . .318
Event Notification Models . . . . . . . . . . . . . . . . . . . . . . . . . .318
The COM+ Event Architecture . . . . . . . . . . . . . . . . . . . . . . .320
ASample LCE Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .323
The EventClass Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . .323
The Subscriber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .325
The Publisher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .329
Running the Sample Application . . . . . . . . . . . . . . . . . . . . .331
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Adding LCE to the Northwind Application . . . . . . . . . . . . . . . . .332
The Northwind Inventory EventClass . . . . . . . . . . . . . . . . .332
The Northwind Inventory Event Subscriber . . . . . . . . . . . .334
The Event Publisher . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .335
ATest Drive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .340
Advanced COM+ Events Topics . . . . . . . . . . . . . . . . . . . . . . . . . .341
Event Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .341
Parallel Event Filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . .345
LCE and Queued Components (QC) . . . . . . . . . . . . . . . . . . .345
Other Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .346
11 Administering COM+ Applications Programmatically . . . . . . . . .349
The COM+ Catalog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .350
The Registration Database and the COM+ Catalog . . . . . . .350
The Catalog Server . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .350
Authority Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .350
The COM+ Admin Objects Model . . . . . . . . . . . . . . . . . . . . . . . . .350
The COMAdmin Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . .351
COM+ Administration Collections . . . . . . . . . . . . . . . . . . . .352
Important Methods and Properties . . . . . . . . . . . . . . . . . . .352
Basic COM+ Administration with the COMAdmin
Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .355
Retrieving Information from COM+ Applications . . . . . . . .355
Retrieving Subscription Information . . . . . . . . . . . . . . . . . .361
Registering a Subscription . . . . . . . . . . . . . . . . . . . . . . . . . .363
Using the RelatedCollectionInfo Collection . . . . . . . . . . . . .365
Creating and Configuring COM+ Applications for
Northwind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .366
Configuring Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . .367
Configuring Compensating Resource Manger . . . . . . . . . . .371
Installing an EventClass . . . . . . . . . . . . . . . . . . . . . . . . . . .373
Subscribe to the Event . . . . . . . . . . . . . . . . . . . . . . . . . . . . .375
Configuring Queued Components . . . . . . . . . . . . . . . . . . . . .378
Using the Windows Scripting Host to Automate COM+
Administration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .382
What Is the Windows Scripting Host? . . . . . . . . . . . . . . . . .382
Using the WSH to Configure Northwind Event
Subscription . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .382
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12 More on COM+ Programming . . . . . . . . . . . . . . . . . . . . . . . . . . .387
Object Constructor Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .388
Shared Property Manager . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .396
Debugging COM+ Components . . . . . . . . . . . . . . . . . . . . . . . . . .401
Object Pooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .406
Missing Pieces of COM+ 1.0 Beta Release . . . . . . . . . . . . . . . . . .407
Part III Building Real World COM+ Services Applications 409
13 Northwind Traders Online: ACOM+ Enabled
Windows DNA2000 Application . . . . . . . . . . . . . . . . . . . . . . . . . .411
Northwind Traders Online: Welcome to the Web . . . . . . . . . . . . .412
The Purpose of the Web Application . . . . . . . . . . . . . . . . . . .412
ABrief Tour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .412
Putting It All Together . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .414
The N-Tiered Application Architecture . . . . . . . . . . . . . . . .414
The Workflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .415
The Presentation Tier: User Services . . . . . . . . . . . . . . . . . .418
The Middle Tier: Business Services . . . . . . . . . . . . . . . . . . .419
The Data Tier: Data Services . . . . . . . . . . . . . . . . . . . . . . . .423
Building the Northwind Traders Online Web Site . . . . . . . . . . . .423
The Login Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .423
The Product Selection Page . . . . . . . . . . . . . . . . . . . . . . . . .430
The Ordering Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .431
The Confirmation Page . . . . . . . . . . . . . . . . . . . . . . . . . . . .434
Testing the COM+ Enabled Web Application . . . . . . . . . . . .437
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .440
14 ACase Study: COM+ and Enterprise Application
Integration (EAI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .443
Introduction to Enterprise Application Integration . . . . . . . . . . .444
The Case Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .444
The Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .444
Original Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .445
The Solution: COM+ and XML . . . . . . . . . . . . . . . . . . . . . . . . . . .447
An XMLPrimer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .449
What Is XML? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .449
Dealing with XMLDocuments . . . . . . . . . . . . . . . . . . . . . . .450