windows workflow foundation (wf)

8/8/2019 Windows Workflow Foundation (WF)

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Adam Cogan & Mark Liu

Windows Workflow Foundation(WF)


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About Mark

Senior Software Architect at SSW

Specialises in

ASP.NET 2.0

Windows Workflow

Windows Communication Foundation

NHibernate / NetTiers / LINQ

SQL Server 2005 (Reporting Service,Integration Service)


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Agenda

Part I - Introduction to Windows WorkflowFoundation What is Workflow? What is Windows Workflow Foundation?

Workflow Types

Part II Workflow Architecture Hosting architecture Built-in Activities

Built-in Services Workflow Persistence Workflow Tracking


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What is Workflow?

Workflow is the operational aspect of awork procedure: how tasks are structured,who performs them, what their relative

order is, how they are synchronized, howinformation flows to support the tasks andhow tasks are tracked.

Source: http://en.wikipedia.org/wiki/Workflow


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What is Workflow?

It is a series of steps that makes up abusiness process

It can involve people I.e. Wait For Approval, Notify Manager

It can co-ordinate software I.e. Check Inventory, Debit Account

It organise them into flowchart or statediagram

It can be short lived I.e. page control, automation It can be long lived

I.e. online auction, approval process


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Introduction to WindowsWorkflow Foundation

It is a framework for rapid development ofworkflow-enabled application

Extensible Programming model

Visual Designer Tool With Visual Studio 2005 and 2008

Workflow Engine In-process workflow engine to support different

architecture scenario


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Key concepts

Workflow is a set ofActivitiesWorkflows run within a HostProcess: any application orserver

Developers can build theirown Custom Activity Libraries Base Activity Library: Out-of-box activities and base forcustom activities

Runtime Engine: Workflowexecution and state management

Runtime Services: Hostingflexibility and communication

Visual Designer: Graphicaland code-based construction

Windows Workflow Foundation

Base Activities Library

Custom Activity Library

Runtime Engine

Runtime Services

A Workflow

An Activity

Visual Designer

Host Process


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Custom Application

How does it hang together?

Add customworkflows

Add customre-usable activities

Add customservices tocommunicate

other systems Host workflow with

Workflow Runtime

Services

Workflow Runtime

Activities

Runtime

Services

Custom

Services

Built-inActivities

CustomActivities

Custom Workflows


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Workflow Types

Sequential Workflow

Looks like a flow chart

State Machine Workflow Looks like a graph


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Sequential Workflow

Characteristics Start from the first activity

Execute in sequence

Limitation Cannot go back to previous activity

without adding Loop

Cannot have two go-back loop thatintersect each other

Inflexible when interacting with

external system, where event ordercannot be guaranteed

Scenario Automation, Document Processing


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Demo: Simple Workflow

Create a Simple Workflow

Create Workflow with Code Activity

Create a Console Application

Create Workflow Runtime

Create HelloWorldWorkflow Instance

Start the Workflow


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State Machine Workflow

Characteristics Event driven

System to system,

Human to system (via application)

Execution based on current State More flexible for external changes

Start with an Initial State and finishes when it reachesCompleted State

Limitation

Cannot create re-usable state activities Designer is buggy with Debugger

Scenario Approval workflow with multiple approval level


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Part II Workflow Architecture


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Hosting Workflow

Workflows are managed and executed byWorkflowRuntime

WorkflowRuntime can be hosted by any

.NET processes Console

Windows Forms

ASP.NET

Windows Service


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Workflow Runtime

Runtime Engine The core layer of the Workflow Runtime Responsible for execution and lifecycle of workflow

Runtime Services

Each service provides a feature that interact with systemoutside the workflow Runtime Services provide features that interact with the

Runtime EngineI.e.

Persistence Tracking Scheduling

Built-in runtime services can be overwrite by customruntime servicesI.e.

Custom OleDbPersistenceService that implements IPersistenceService tostore workflow state into any OleDB database.


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Activities

Building blocks of workflow Represent unit of execution, re-use and composition

Basic activities are steps within a workflow

Composite activities contain other activities

Activities are classes Properties and events are defined by activity author and

programmable from the workflow

Inherit from System.Workflow.ComponentModel.Activityclass

Contain methods that are invoked by the WorkflowRuntime (E.g. Execute)

Can be built into workflow assembly or deployed as re-usable libraries

Best Practice: keep workflow and activities in separate projects


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Activities

Activities can have conditions

Code condition A specific method, created by Activity Author, that returns

true or false

The code condition is compiled into the assembly

Declarative condition A single declarative condition that results in true or false

The declarative condition is interpreted and is allowed to be

modified after compilation Policy condition

A rule set in a policy derived activity consisting of acollection of conditions and resultant actions


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Built-in Activities

Control flow activities

Sequence

Parallel

IfElse

While

ConditionedActivityGroup

Replicator


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Built-in Activities

Lifetime activities

InvokeWorkflow

Suspend

Terminate

Event waiting activities

EventDriven

Listen

Delay

HandleExternalEvent


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Built-in Activities

Web service activities

Invoke webservice

WebServiceRequest

WebServiceResponse

Other

InvokeExternalMethod


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Demo: Building CustomActivities

Build a ConsoleWrite activity

Update Hello World workflow


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Transaction in WindowsWorkflow

Transaction:

Atomic (ACID)

Behave like System.Transactions.TransactionScope

Cannot be nested

Exception handlers not permittedLong-Running activities

May contain atomic or other Long-Running Processes

May be nested to arbitrary depths


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Introducing CompensatingLogic

Transaction is not suited for long runningprocesses. You cannot lock a table for 3 days!

Need a mechanism to reset committedinformation when a problem is encountered

For example

Need to return inventory to stock when customercancel order


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Activities with CompensationLogic

Long-running workflow

Atomic Transaction

Get Item

De-queueItem

Queue DB

Queue DB

Compensation Handler

QueueItem Queue DB

Normal Execution

Compensating LogicExecuted only if error occursafter the related transaction

was properly submitted


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Compensating Flow

Long-running workflow

Atomic Transaction 1 Compensation Handler 1

Re-queue Item DB

Atomic Transaction 2

Process Item DB

Get Item

De-queue Item

DB

DB

Compensation Handler 2

Cleanup Item DB

If transaction 1 commits and transaction 2 fails then compensation handler 1 will be executed

The item will be re-queued into the database


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Runtime Services

Workflow Loader Service Creates workflow instance based on class type or XML

definition

Built-in: Default Workflow Loader Service

Workflow Scheduler Service Allocate thread to the Runtime Environment to execute

the workflow

Built-in: Default Scheduler Service The default scheduler service created by Runtime if none is specified

Multi-threaded create and manages its own thread pool to execute

workflows Used in Windows Form, Console and Windows Service apps

Built-in: Manual Scheduler Service Single threaded only use the thread donated by the caller

Used in ASP.NET apps


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Runtime Services

Persistence Service Stores and loads workflow state into durable storage

Built in: SqlWorkflowPersistenceService Store workflow state in SQL Server

Database scripts can be found in:C:\Windows\Microsoft.NET\Framework\v3.0\Windows WorkflowFoundation\SQL\EN

Tracking Service Track state of the workflow

Track execution history

Built in: SqlTrackingService Support customizable tracking criteria

Store tracking history in SQL Server

Supports customizable tracking

See above for database scripts


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Runtime Services

WorkflowCommitWorkBatchService

DefaultWorkflowCommitWorkBatchService Uses MSDTC

SharedConnectionWorkflowCommitWorkBatchService

Tracking and Persistence schema must be on the samedatabase

Avoid MSDTC by sharing database connection between

persistence and tracking


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Workflow Persistence

Saving and loading workflow state from adurable state Built-in SQL Server support

Sample code on persisting to text files Supports long-running processes

Serializing workflow is expensive

Workflow Runtime only persist when

Transaction Scope completes Workflow is unloaded

Workflow idles past the configured time


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Demo: ConfiguringPersistence Service

Configure database

Configure Workflow Runtime

Demonstrate persistence on:

Transaction

Idle

Unload


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Workflow Tracking

Generic API that allow applicationdevelopers to track:

Execution status of the workflow / activities

Properties in the workflow / activities User-defined track point inside the workflow

Tracking are filtered by a Tracking Profile


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Workflow Tracking

Built-in SqlTrackingService provides:

Store tracking data to SQL server

Customizable Tracking Profile by WorkflowType No built-in designer

Query objects to retrieve tracking data

Limitation of SqlTrackingService:

Stores data in an highly normalized and generic schema,difficult to get a specific value for a workflow

Lack of built-in designer to create custom trackingprofile

Lack of built-in tools to view the tracked data

There are sample code that does both


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Demo: Building ConsoleTracking Service

Create tracking profile in code

Write tracking record to console window


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Demo: Configuring SQLTracking Service

Setup Sql Tracking Service

Review result with wfsample Monitor tool


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Communicating with Host

Host cannot interact directly with the workflow ExternalDataExchangeService is a runtime service that

simplifies communication between workflow and host Communication from host-to-workflow works by:

Host process raises an event defined in a service object

Runtime passes the event arguments to the correct Workflow Event Arguments must inherit

System.Workflow.Activities.ExternalDataEventArgs Event must be declared on an interface marked with

System.Workflow.Activities.ExternalDataExchangeAttribute User-defined service object must implement the said interface

Communication from workflow-to-host works by: Workflow request a service object from Workflow Runtime that

implements a specific Interface type Workflow invoke a method directly on the service object


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Demo: BuildingCommunication Service

Add events to Console Service

Consume events from Workflow


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Demo: State MachineWorkflow

case-study of a simple approval system


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Contact Details

[email protected]

[email protected]


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