Book Image

Programming Windows Workflow Foundation: Practical WF Techniques and Examples using XAML and C#

By : Kenneth Scott Allen
Book Image

Programming Windows Workflow Foundation: Practical WF Techniques and Examples using XAML and C#

By: Kenneth Scott Allen

Overview of this book

Windows Workflow Foundation (WF) is a technology for defining, executing, and managing workflows. It is part of the .NET Framework 3.0 and will be available natively in the Windows Vista operating system. Windows Workflow Foundation might be the most significant piece of middleware to arrive on the Windows platform since COM+ and the Distributed Transaction Coordinator. The difference is, not every application needs a distributed transaction, but nearly every application does have a workflow encoded inside it. In this book, K Scott Allen, author of renowned .NET articles at www.odetocode.com, provides you with all the information needed to develop successful products with Windows Workflow. From the basics of how Windows Workflow can solve the difficult problems inherent in workflow solutions, through authoring workflows in code, learning about the base activity library in Windows Workflow and the different types of workflow provided, and on to building event-driven workflows using state machines, workflow communications, and finally rules and conditions in Windows Workflow, this book will give you the in-depth information you need. Throughout the book, an example "bug reporting" workflow system is developed, showcasing the technology and techniques used.
Table of Contents (14 chapters)
Programming Windows Workflow Foundation: Practical WF Techniques and Examples using XAML and C#
Credits
About the Author
About the Reviewer
Preface

Persistence Services


Persistence services solve the problems inherent in executing long-running workflows. Many business processes take days, weeks, and months to complete. We can't keep workflow instances in memory while waiting for the accountant to return from the beaches of Spain and approve an expense report.

Long-running workflows spend the majority of their time in an idle state. The workflow might be idle waiting for a Delay activity to finish, or for an event to arrive in a HandleExternalEvent activity. When a persistence service is available, the runtime can persist and then unload an idle workflow. Persistence saves the state of the workflow into long-term storage. When the event finally arrives, the runtime can restore the workflow and resume processing.

The workflow runtime decides when to persist workflows, and the persistence service decides how and where to save the workflow state. The runtime will ask the persistence service to save a workflow's state when a workflow goes...