The basic architecture of Windows Workflow Foundation is
comprised of the following layers.
·
The Hosting Layer
·
The Runtime Layer
·
The Workflow Model Layer
The Hosting Layer is one that
provides pluggable interfaces between Windows Workflow and a specific host. Note
that a host can be a Web Application, a Web Service, etc. The services provided
by this layer include:
·
Persistence services
·
Thread support
·
Communication Support
·
Timer services
The Runtime Layer is a
non-pluggable layer as is the core of the WWF architecture and is responsible
for Workflow management and Workflow Execution. The basic services provided by
this layer include the following.
·
Workflow Execution
·
Workflow State Management
·
Workflow Activity Scheduling
·
Rules and Policy Management
The Workflow Model Layer provides
the API for working with Windows Workflow Foundation in .NET framework. Basically,
the Workflow Model Layer defines two models.
·
The Sequential Workflow Model
·
The State Machine Workflow Model
The following sections discuss both these models with a self
explanatory diagram in each case.
The Sequential Workflow Model
The Sequential Workflow model is used to depict structured
workflows like a System to System Workflow. The steps in such a Workflow Model
are organized in a sequence.
Figure 1
The State Machine Workflow Model
In this type of a non-deterministic, non-sequential people
centric Workflow Model, we find a representation of states and transitions
between these states that typically represent a Workflow. The State Machine
workflow Model is also known as the State Driven Workflow Model. The diagram
shown in the figure below illustrates a typical State Machine Workflow Model.
Figure 2
