Microsoft Press Windows Workflow Foundation Step By Step

486 Pages·2007·8.088 MB·English

by  Kenn Scribner

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Copyright © 2007 by Kenn Scribner
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iii
Table of Contents
Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .v
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xv
Part I Introducing Windows Workflow Foundation (WF)
1 Introducing Microsoft Windows Workflow Foundation. . . . . . . . . . . . . . 3
Workflow Concepts and Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Enter the Operating System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Multithreading and Workflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Comparing WF with Microsoft BizTalk and WCF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Beginning Programming with WF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Visual Studio Workflow Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Building Your First Workflow Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Chapter 1 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
2 The Workflow Runtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Hosting WF in Your Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
A Closer Look at the WorkflowRuntime Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Building a Workflow Runtime Factory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Starting the Workflow Runtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Stopping the Workflow Runtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Subscribing to Workflow Runtime Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
Chapter 2 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
3 Workflow Instances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
Introducing the WorkflowInstance Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Starting a Workflow Instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
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v
vi Table of Contents
Starting a Workflow Instance with Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Determining Workflow Instance Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Terminating a Workflow Instance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Dehydration and Rehydration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Chapter 3 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4 Introduction to Activities and Workflow Types. . . . . . . . . . . . . . . . . . . . 57
Introducing the Activity, the Basic Unit of Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
The ActivityExecutionContext Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Dependency Properties 101 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Activity Validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Workflow Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Selecting a Workflow Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
The Sequence Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
Building a Sequential Workflow Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
The State Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
Building a State Machine Workflow Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
Chapter 4 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5 Workflow Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Pluggable Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Workflow Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
Workflow Event Tracking Using SqlTrackingService . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Setting Up SQL Server for Tracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
Using the SqlTrackingService Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Tracking User Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Building Custom Tracking Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
Viewing Tracking Information with WorkflowMonitor . . . . . . . . . . . . . . . . . . . . . . . . 96
Chapter 5 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
6 Loading and Unloading Instances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Persisting Workflow Instances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Setting Up SQL Server for Persistence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
Introducing the SqlWorkflowPersistenceService Service . . . . . . . . . . . . . . . . . . . . . . 106
Unloading Instances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
Loading Instances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Loading and Unloading Instances on Idle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Chapter 6 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Table of Contents vii
Part II Working with Activities
7 Basic Activity Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
Using the Sequence Activity Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127
Using the Code Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131
Using the Throw Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131
Using the FaultHandler Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .137
Quick Tour of the Workflow Visual Designer . . . . . . . . . . . . . . . . . . . . . . . . . . .138
Using the Suspend Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .145
Using the Terminate Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .148
Chapter 7 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .150
8 Calling External Methods and Workflows. . . . . . . . . . . . . . . . . . . . . . . . 151
Building an ExternalDataService Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152
Workflow Intraprocess Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152
Designing and Implementing Workflow Intraprocess Communication . . . .153
The Motor Vehicle Data-Checking Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .154
Creating Service Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .156
Using the ExternalDataExchange Attribute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157
Using ExternalDataEventArgs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159
Creating External Data Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160
The CallExternalMethod Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170
Creating and Using Custom External Data Service Activities . . . . . . . . . . . . . . . . . .170
Receiving Workflow Data Within the Host Application . . . . . . . . . . . . . . . . . . . . . . .174
Invoking External Workflows with InvokeWorkflow . . . . . . . . . . . . . . . . . . . . . . . . . .177
Chapter 8 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181
9 Logic Flow Activities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183
Conditions and Condition Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .183
The Questioner Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184
Using the IfElse Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .185
Using the While Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .195
Using the Replicator Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .199
Chapter 9 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .208
10 Event Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
Using the HandleExternalEvent Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .209
Using the Delay Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .211
Using the EventDriven Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .212
viii Table of Contents
Using the Listen Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
Using the EventHandlingScope Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
Host-to-Workflow Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
Creating the Communication Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
Chapter 10 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
11 Parallel Activities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
Using the Parallel Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
Using the SynchronizationScope Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
Using the ConditionedActivityGroup (CAG) Activity . . . . . . . . . . . . . . . . . . . . . . . . . . 253
Chapter 11 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
12 Policy and Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
Policy and Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
Implementing Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
Rule Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
The Update Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
Rule Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
Forward Chaining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
Implicit Chaining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279
Attributed Chaining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
Explicit Chaining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
Controlling Forward Chaining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
Controlling Rule Reevaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
Using the Policy Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
Chapter 12 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
13 Crafting Custom Activities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
More About Activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
Activity Virtual Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
Activity Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
Execution Contexts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
Activity Lifetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
Creating an FTP Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
Creating a Custom ActivityValidator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
Providing a Toolbox Bitmap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314
Tailoring Activity Appearance in the Visual Workflow Designer . . . . . . . . . . . . . . . 315
Integrating Custom Activities into the Toolbox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
Chapter 13 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
Table of Contents ix
Part III Workflow Processing
14 State-Based Workflows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
The State Machine Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .327
Using the State Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .328
Using the SetState Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .328
Using the StateInitialization Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .329
Using the StateFinalization Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .330
Creating a State-Based Workflow Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .330
Chapter 14 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .346
15 Workflows and Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
Understanding Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .347
Classic (XA) Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .348
Initiating Transactions in Your Workflows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .351
Workflow Runtime and Transactional Services . . . . . . . . . . . . . . . . . . . . . . . . .351
Fault Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .352
Ambient Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .352
Using the TransactionScope Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .352
Committing Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .353
Rolling Back Transactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .354
Using the CompensatableTransactionScope Activity . . . . . . . . . . . . . . . . . . . . . . . . . .354
Using the Compensate Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .355
Using the CompensatableSequence Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .356
Creating a Transacted Workflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .357
Chapter 15 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .371
16 Declarative Workflows. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
Declarative Workflow—XML Markup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .374
Declaring Namespaces and Namespace Association . . . . . . . . . . . . . . . . . . . . . . . . .375
Creating and Executing XAML-Based Workflows . . . . . . . . . . . . . . . . . . . . . . . . . . . .377
Chapter 16 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .390
17 Correlation and Local Host Communication. . . . . . . . . . . . . . . . . . . . . . 391
Host and Workflow Local Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .391
Correlation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .392
The CorrelationParameter Attribute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .394
The CorrelationInitializer Attribute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .394
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The CorrelationAlias Attribute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
Building Correlated Workflows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
Chapter 17 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430
18 Invoking Web Services from Within Your Workflows. . . . . . . . . . . . . . 431
Web Services Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431
Using the InvokeWebService Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 432
Adding the Web Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434
Configuring the Proxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
Static Proxy Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
Dynamic Proxy Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
Working with Sessions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436
Long-Running XML Web Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437
Building a Workflow That Uses an XML Web Service . . . . . . . . . . . . . . . . . . . . . . . . 438
Chapter 18 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443
19 Workflows as Web Services. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445
Exposing a Workflow as an XML Web Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445
Creating the Workflow Runtime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
Configuring Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448
Workflow Housekeeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
Using the WebServiceInput Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
Using the WebServiceOutput Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
Using the WebServiceFault Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
Creating a Host Web Service Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
Chapter 19 Quick Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 468
Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 469
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Foreword
To me, workflow engines such as Microsoft BizTalk always seemed like a really expensive
thing that I didn't need for many projects. I always thought, “How hard can it be to actually
code the logic you draw on the screen?” As a result, I spent a lot of time not learning what a
workflow engine could do for me and, instead, lived with “just code.” Still, I was intrigued and
would bug my friends about what they saw as the value of BizTalk. They would usually get me
excited enough to try installing the product and learning how it worked. Every time I tried to
make the plunge and learn how to use BizTalk, I backed away because it seemed too complex
for what I perceived as a flowchart execution engine.
Sometime around 2003, while working at Microsoft on what was to become Windows
Communication Foundation, I heard about a general-purpose workflow engine being built
within Microsoft. Rumor had it that the workflow engine might even be integrated into the
operating system! The reason: Prior to then, groups within Microsoft had created their own
workflow engines for their own problem domains. Most of the engines were written in C++
and exhibited limited flexibility outside of their domain area. BizTalk, which had a general-
purpose engine, was not then designed to have its engine separated from the BizTalk product.
What Microsoft discovered was there was a real need for a single, general-purpose workflow
engine so that internal Microsoft teams could stop reinventing workflow. This realization
(which occurred prior to me hearing anything) helped create what would eventually become
the Windows Workflow Foundation team.
As a part of .NET Frameworks 3.0, Windows Workflow Foundation is a freely distributable
.NET component. On Windows Vista and later, it ships as a part of the operating system.
What doesthis mean for developers? It means that they can learn how to use a workflow
engine and distribute their applications while being able to rely on a workflow engine just
being present on the client machine. Bigger applications will still need tools such as BizTalk
Server to manage workflows. But, for smaller applications that could use some of the benefits
of workflow (such as state machines and the ability to suspend and resume a workflow),
Windows Workflow Foundation is a godsend.
The book you now hold shows all the little things that Windows Workflow Foundation can
do. Because it is the introductory book to Windows Workflow Foundation, it takes a tour of
the feature set and lets you know what is available. For me, this book has served as a great
introduction to the technology. I have discovered that most projects would benefit from a
healthy dose of workflow somewhere. Thesamples in this book proved as much to me.
Kenn, congratulations on finishing up a great book. Thank you for making me a part of the
process. I believe many more .NET developers will finally understand what workflow can do
for them thanks to your introduction to the topic.
Scott Seely
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