Sam Gentile's Blog (if (DeveloperTask == Communication && OS == Windows)

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