《WF in 24 Hours》读书笔记 - Hour 1 - Understanding Windows Workflow Foundation

1.1 Hour 1 -
Understanding Windows Workflow Foundation

1.1.1 What workflow is
in general

• A workflow is logic-consisting of one or more steps that are predicated by
  one or more conditions-that a system or person must perform to complete a
  function. Because the logic or process automated by a workflow generally
  consists of more than one step that may occur over a period of time, it must
  track the state of the overall process. Here are some examples of workflows:
  an order process, an expense report, and rescheduling a missed meeting.

• In short, workflow consists of both logic and managing the process
  state.


• benefits:
  
  1. Design-time transparency
  
  
  2. State management
  
  
  3. Runtime transparency

1.1.2 What Windows
Workflow Foundation (WF) is

1.1.3 The main
components of WF one-by-one

• Standard Modeling Activities Activities are the unit of design and
  execution in WF. WF comes with a set of modeling constructs that it calls
  activities and a workflow designer. WF ships with approximately 30 activities.
  It calls these activities the Base Activity Library (BAL). The activities are
  largely segmented as follows: control flow activities, activities that
  facilitate data exchange between the workflow and the application running the
  workflow (a Windows Forms application, for example), one that permits
  arbitrary code to be written, and another group that supplies exception
  handling.
  
  1. control flow activities
     
     1. Sequence: a shell for other activities. It is equivalent to {}in C#.
        It is a block where activities may be added. A Sequenceactivity can hold a
        tree of activities.

1. While: loops while the condition associated with it remains true.

1. IfElse: holds one or more branches that are each governed by a condition.
   The first branch to return trueis executed; no other branches are
   executed.

1. Listen: allows two or more branches to be added that each wait for an
   external event.


2. Parallel: executes two or more branches concurrently. TheParallel activity
   will wait

for all branches to complete before completing.

1. Replicator: can process a number of elements specified at runtime and can
   do so in serial or parallel. It is similar to the C# foreach statement with
   the additional capability to process in parallel as well as sequentially.

1. EventHandlingScope: is similar to a Listenactivity but it allows the
   events to be received multiple times.

1. data exchange activities
   
   1. CallExternalMethod: is used to send data from the workflow to the
      application running the workflow (the host).
   
   
   2. HandleExternalEvent: allows data to be sent from the

host to the workflow.

1. WebServiceOutput and WebServiceInput: expose a workflow as a web
   service

1. InvokeWebService: call a web service from a workflow


2. Send: is used to connect to a WCF endpoint (or any compatible endpoint)
   from a workflow.


3. Receive: is used to expose a workflow as a WCF Service.


4. Code: points to a handler with standard .NET code. It can be used to add
   custom functionality to a workflow, although in many cases it is better to use
   a custom activity.

1. Multiple Workflow Styles
   
   1. ConditionedActivityGroup: can be placed on both sequential and state
      machine workflows.

1. sequential workflows: are recommended for deterministic processes that
   have a well-defined beginning and end.


2. State machine workflows: are best suited for dynamic processes that
   iterate through states without a guaranteed order.

1. Data-driven workflows: are best suited when the data determines the
   process execution order.


2. In essence, a state machine workflow is an inverse sequential workflow.
   The events are on top and the sequential logic embedded when using a state
   machine workflow. In a sequential workflow it is the opposite.

1. Hosting
   
   • WF is not a standalone application. WF is an engine that executes
     workflows on behalf of a host application. A Windows Forms, ASP.NET, Windows
     Service, or other Windows application starts the workflow engine running.
     The host application is then responsible for managing the life cycle of the
     workflow engine. The host application must remain active while workflows are
     running and communicate with the workflow engine. If the host application
     terminates while workflows are running, they will stop running. The host
     application needs to know the status of workflows the workflow engine is
     running on its behalf. It achieves this by subscribing to a number of events
     the workflow engine makes available to it. Three of the most common are
     completed,terminated, and idled.

1. completed event: fired when a workflow completes processing
   successfully.


2. terminated event: fired when the workflow completes unsuccessfully.


3. idled event: the workflow is not complete but inactive.

1.1.4 Installation
instructions and requirements

《WF in 24 Hours》读书笔记 - Hour 1 - Understanding Windows Workflow
Foundation