Window Workflow Foundation - A new way to develop workflow

I’ve recently reviewed the new workflow framework called Windows Workflow Foundation ( WWF ) which is part of the .NET framework 3.0 runtime. Using the framework successfully within our applications will require a completely different thought process on traditional methods e.g. where we typically put most of the workflow behaviour directly within the code.

I started to develop a generic workflow framework implementation of core business object services a few years back, however even with considerable effort, the implementation lacks many of the features provided by WWF. Given that most business applications go some way to make them flexible by developing a generic workflow framework, use of WWF should allow most teams to concentrate more on the back end business logic rather than trying to do what WWF does very well.

I would highly recommend reading Bruce Bukovics excellent WWF book http://www.apress.com/book/bookDisplay.html?bID=10213 which provides coverage of all the important features in WWF very clearly.

I have summarised the main points of WWF below

General Points

1. Multiple types of workflow – It handles both sequential and state machine workflows, although typically P2P / Banking applications which Bottomline develops use state machine workflows because the processes don't define a fixed flow of control within the workflow.
2. Scalability - The ability of a workflow to persist itself could allow multiple servers to be workflow runtime hosts and therefore a workflow could be loaded and executed on a different server than the one that started it.
3. Workflow tracking - This is one of the most powerful features of WWF. However whilst it provides rich support for tracking the workflow through the different stages in the lifecycle, it also tracks rules. Rules evaluation records each rule or rule set as it is evaluated. This could also help to easily explain to users why the workflow has progressed in a particular way. You can even go further and use custom tracking profiles to track the values of the entities at particular points in time when for example a rule was evaluated. This provides a complete tracking picture for rules evaluation
4. Hosting of workflow designers - The tools to host the designer tools within your own applications are exposed and available as part of the WWF framework. This allows you to create even simple designer interfaces very easily e.g. allowing a user to create a number of different states within a state machine and chain them together to describe how each state transitions to the next and the event which cause the transition.
5. Parallel execution of activities within a workflow – Whilst activities cannot execute truly concurrently within a workflow the framework does support execution of two parallel branches of activities in that the first activity of the first branch will execute, when this finishes, the first activity in the second branch executes and so on
6. Exception handling – Provides support for handling exceptions in the workflow e.g. if activities which are part of the workflow do not complete as expected, different activities can be called and activities cleaned up correctly. Related to this is compensation which allows an activity to be undone rather than rolled back, when typical long running transactional flows could not possibly maintain a database transaction for a long period of time.

Rules

1. The rules and workflow data can be specified in an XML based format which is compiled by the WWF into code making it very quick to execute at runtime. The rules files can either be created manually or modified through using a rules designer.
2. Very feature rich rules can be created e.g. if you have access to the invoice entity you could say if Invoice.LineItems.Count > 1 then HasMultipleLineItems, and then write control of flow in your workflow using this rule.
3. Support for forward chaining of rules also means that you don't need to be so concerned with the order or priority you specify rules in. If a rule further down in a list of rules causes fields to change for which previous rules relied upon, this will cause those previous rules to be re-evaluated. Although you can override this for specific rules and specify a priority and indicate you don’t want any forward chaining to occur

Persistence of workflow

1. Objects associated with the workflow are serialized and de-serialised seamlessly. E.g. an invoice workflow object may require references to the invoice itself, and perhaps related purchase orders.
2. Handles the persistence of the workflows in the database or any other data store as required. Given the complex workflows you can create this support coming out of the box is a big plus. Not only is the workflow itself persisted i.e. the current state machine workflow , but all the associated rules and rule sets that the workflow contains
3. Workflow versioning / Dynamic workflow updates - Versioning is also handled well i.e. as you evolve your workflows and add new activities, create new or modify existing rules. Multiple entities can therefore exist which are associated with older and newer workflows. Although conversely with very long running workflows e.g. when a process will take a considerable time to complete you may want to change an existing workflow, this is also supported through dynamic updates.

Integration

1. Publishing of workflows – Workflows can be published as web services, which provide very powerful integration features to third party systems. This enables applications to call into the workflow and take appropriate actions e.g. approve an invoice.
2. Workflow chaining - Allows you to chain workflows together i.e. call one entirely new workflow from within an activity of another workflow.
3. Activities within workflows can call into web services, which provide easy integration points into many different ERP systems.

State machine workflows

1. Support complex state machines - Support for recursive composition of states which effectively means states can contains other states i.e. any events defined by the outer state are available while the workflow is currently in any of the inner states. This allows more elegant state machines to be designed which don’t contain redundant activities e.g. for an invoice a Cancel activity could be defined in a single state rather than all possible states from which the invoice could be cancelled.
2. Visibility of permissible events - The framework provides support within state machine workflows to easily see which events can be called when the workflow is in a specific state. We can easily see how this would be useful e.g. for invoices to determine which action buttons to display such as "Approve" could be driven on whether the "Approve" event is available. This would also facilitate external components knowing the events which they could call through a web service interface.

Using WWF should allow you more time to concentrate on the development of the business logic and also reduce the risks that are inherent in building a generic workflow framework.