05 December 2006

First steps in Workflow Foundation

I have started to play with Windows Workflow Foundation (WF) a few days ago. So far it seems very interesting, shipping with handy pre-build activities, persistence and tracking services, prity designers for visual studio, the capability of hosting these designers anywhere else…web services interaction, etc. Promising.

I just want to take down some notes here so I don't forget what I've learned.

Some Material

Some Concepts
  • Windows Workflow Foundation (WF): Set of components, tools, and a designer that developers can use to create and implement workflows in .NET Framework applications. It is part of the Microsoft .NET Framework version 3.0.
  • Workflow: a set of activities that are stored as a model that describes a real-world process. A workflow is designed by laying out activities.
  • Activity: A step in a workflow. The unit of execution, re-use and composition for a workflow.
  • Types of workflows (Here is a post about how to decide which type to use):
    • Sequential: Consists of activities that execute in a predefined order. Has a clear direction of flow from top to bottom, although it can include loops, conditional tests, and other flow-control structures.
    • State-Machine: Consists of states and transitions that change a workflow instance from one state to another. Although there is an initial state and a final state, the states have no fixed order, and an instance can move through the workflow in one of many paths.
    • Data-Driven: Is usually a sequential workflow that contains constrained activity groups and policies. In a data-driven or rules-based workflow, rules that check external data determine the path of a workflow instance. The constrained activities check rules to determine the activities that can occur.

The framework component model

The WF framework consists on 3 assemblies, containing the following namespaces:

  • System.Workflow.Activities
    • System.Workflow.Activities: Defines activities that can be added to workflows to create and run an executable representation of a work process.
    • System.Workflow.Activities.Configuration: Provides classes that represent sections of the configuration file.
    • System.Workflow.Activities.Rules: Contains a set of classes that define the conditions and actions that form a rule.
    • System.Workflow.Activities.Rules.Design: Contains a set of classes that manage the Rule Set Editor and the Rule Condition Editor dialog boxes.
  • System.Workflow.ComponentModel
    • System.Workflow.ComponentModel: Provides the base classes, interfaces, and core modeling constructs that are used to create activities and workflows.
    • System.Workflow.ComponentModel.Compiler: Provides infrastructure for validating and compiling activities and workflows.
    • System.Workflow.ComponentModel.Design: Contains classes that developers can use to build custom design-time behavior for workflows and activities and user interfaces for configuring workflows and activities at design time. The design-time environment provides systems that enable developers to arrange workflows and activities and configure their properties. The classes and interfaces defined within this namespace can be used to build design-time behavior for activities and workflows, access design-time services, and implement customized design-time configuration interfaces. It includes the TypeBrowserEditor, a cool feature that can be reused.
    • System.Workflow.ComponentModel.Serialization: Provides the infrastructure for managing the serialization of activities and workflows to and from extensible Application Markup Language (XAML) and CodeDOM.

  • System.Workflow.Runtime
    • System.Workflow.Runtime: Classes and interfaces that control the workflow runtime engine and the execution of a workflow instance.
    • System.Workflow.Runtime.Configuration: Classes for configuring the workflow runtime engine.
    • System.Workflow.Runtime.DebugEngine: Classes and interfaces for use in debugging workflow instances.
    • System.Workflow.Runtime.Hosting: Classes that are related to services provided to the workflow runtime engine by the host application.
    • System.Workflow.Runtime.Tracking: Classes and an interface related to tracking services.

Wix install sequence

I am trying to figure out the exact behavor of the install sequence in the setup, as defined in a wix .wxs file. The confusion comes from the presence of the InstallUISequence and the InstallExecuteSequence tags, leaving aside the fact that there are actually four tags related to the actions sequence (AdminUiSequence and AdminExecuteSequence are used in administrative installs). As it is said in the wix turorial, "InstallExecuteSequence is always consulted by the installer to determine the actions, InstallUISequence is only considered when the installer runs in full or reduced UI mode." So, if executing without user interface, the order is determined for the InstallExecuteSequence and no doubts remain. But, if executing in full or reduced UI mode, both sequences are consulted. So, what is the resulting order of execution? If an action is placed in both sequences, it is executed twice?

As for the executing order, what I suppose happens is that all actions in the InstallUISequence are run first (since they gather the information required for the installation) and then those from the InstallExecuteSequence. But it is possible that some actions need to be executed before any UI dialog, so then we should place them in both sequences.

If an action is placed in both sequences, they will be apparently executed twice. Al least one exception for this rule is the AppSearch action. In the schema reference it says: “AppSearch should be authored into the InstallUISequence table and InstallExecuteSequence table. The installer prevents The AppSearch action from running in the InstallExecuteSequence sequence if the action has already run in InstallUISequence sequence.”

For custom actions, the execute attribute can be used for preventing the double execution.