Live Blog - Day 3 Pluralsight BizTalk Course - Introduction to Windows Workflow Foundation

I thought today may be a good topic for my audience as it go well together with my 3 part WF series just as some of yesterday augments this post on WCF 101.

• WF Windows Workflow Foundation
• WF is a Framework for building Workflow-enabled applications
• It is NOT a Workflow "product"
• CLR-based extensible framework
• Re-hostable runtime and toolset (design tools, compiler)
• Royalty-free
• Part of .NET 3.0
• Ships in Windows Vista
• Microsoft's Workflow Engine
• WF will be the workflow engine for all workflow-enabled Microsoft products going forward
• Windows SharePoint Services 3.0
• Speech Server
• BizTalk Server 200x
• All future products requiring workflow capabilities
• Activity
• Base class of all base classes in WF
• A Workflow is a tree of Activities
• An Activity is the atom of execution
• WF includes a rich set of built-in Actvities
• Custom Activities are almost a certainty for any application that uses WF
• OOB Activities
• Grouped into
• Flow
• State-Based
• Rule-based
• Communication
• Misc.
• Activities and the Runtime
• WorkflowRuntime can operate on any single valid Activity
• It doesn't differentiate one Activity from another
• Most apps will execute on an Activity which is a composite
• Child Actvities executed by parent
• WF comes with two typical "root" models
• SequentialWorkflowActvity
• One of two built-in top-level Actvities
• Path of execution is more predetermined
• Contains other Activities
• Useful model when workflow needs to be in charge of execution path
• Example: Document-approval workflow with limited steps
• StateMachineWorkflowActivity
• Modeled as a set of distinct states
• State transitions used to move from one possible state to another
• Useful model when user or host needs to have influence on execution path
• Example: Document-approval with a dynamic number of steps
• Rules
• WF contains a full-featured rule engine
• Rule-based conditions
• Policy Activity
• Custom rule-based Activities possible
• Dynamic execution model enables runtime changes
• Rule-based model useful for many algorithms
• WorkflowRuntime
• Controls execution of workflows with a very specific model
• Provides access to services
• Mediates communication between host and workflow
• Creates and manages workflow instances
• Host controls workflow usage through WorkflowRuntime Type
• Host plays a significant role in the behavior of the WorkflowRuntime
• Services
• Runtime relies on services
• IServiceProvider model
• Services are singletons per WorkflowRuntime
• Well-known services derive from WorkflowRuntimeService and derived classes
• Can be done with code or config
• Any type can be a service (Runtime needed to know about all services)
• You must...
• Some services are required, defaults will be used if not configured
• Scheduler
• Batch (transactions)
• WorkflowLoading
• If you build it...
• Runtime will automatically use certain services if found (discover based on base class)
• Tracking
• Persistence
• OOB implementations
• Many optional services have OOB implementations
• SqlWorkflowPersistenceService
• SqlTrackingService
• Custom services
• Custom services likely for most WF usage models
• Custom tracking
• Persistence
• Other "services" needed by Actvities added to runtime by hosting environment
• Communication
• Runtime must control between host and workflow
• The runtime model requires the ability to persist at any time
• Host can't have real reference to workflow objects
• Communication enabled through queues
• Higher-level abstractions built on top of queues
• Data must be serialized
• Hosting
• The layer of code that uses the WorkflowRuntime
• Can be any-CLR enabled app
• No standard default host
• Host is app-specific
• A basic WebService (asmx) host is provided
• Host responsible for bootstrapping the WorkflowRuntime
• Host is responsible for adding services
• Workflow Execution
• Host must create workflows through the runtime
• WorkflowRuntime.CreateWorkflow can take any type if Activity (i.e. Workflow need not be just StateMachine or Sequential)
• WorkflowRuntime.CreateWorkflow overload takes XAML (XmlReader)
• WorkflowInstance can be used to start workflow
• Parameters
• Parameters are passed to a workflow when created
• Dictionary<string,object> is container
• Workflow defines public properties
• A read-only copy of properties available after workflow completion
• Designer
• Visual creation of workflows
• Designer built into Visual Studio
• Designer can be hosted as control in other apps
• Themed (custom themes possible)
• Compilation
• Workflows can be expressed in code
• Activity tree compiled into assembly
• Executed by loading .NET type
• VS.NET designer uses typical model (InitializeComponent to create tree)
• XAML
• Workflows can be expressed in XAML (XML markup)
• Key for workflow apps (ease of authoring)
• Ease of use in dynamic situations
• You will beed code-based Activities more than if using compiled workflows
• WorkflowRuntime can create workflows from an XmlReader
• WFC
• Workflow compiler
• Used to compile XAML-or code-based workflows
• Can compile XAML and "code behind"
• Outputs assembly
• Not all XAML is created equal
• XAML can either be executed (CreateWorkflow) or compiled - not both
• Presence of Class attribute is key factor
• Dynamic Change
• In-Memory workflows can be modified
• Activities can be added or removed
• Adaptive scenarios possible (e.g. escalation)
• Change affects single Activity
• Changed Activity *could* be persisted (into an assembly or as markup)
• XAML-based workflows must be appropriate for planned dynamic change
• Why Workflow?
• Many applications' logic are really workflows
• Web app page flow
• Form wizards
• Service compositors
• Long-running processes
• Workflow Possibilities
• WF is a multi-purpose runtime for executing code
• Could be used for a simple workflow inside of an application (algorithm usage)
• Customizable and/or dynamic workflow system
• Vertical or Horizontal Workflow Product (including Microsoft projects