1. Persistence Framework API A set of persistent interfaces that define the contract with Workflow Service Host to persists its state. These enable you to build any type of persistence provider from database backed to say distributed in-memory cache.
2. The SQL Workflow Instance Store (SWIS) implements the abstract class InstanceStore of the Persistence Framework API. This class is used by the Workflow Service Host to create, load, save and delete durable instance data.
3. The SQL Server Persistence database stores all the durable instance state. It also stores the additional metadata that is used to activate and recover a service instance.
4. The Workflow Management Service (WMS) is a Windows Service that activates a Workflow Service Host whenever there are unloaded instances with expired durable timers, instances that need to be reactivated after a graceful shutdown or instances that need to be recovered after a crash. The WMS is also involved in the execution of instance control commands, which will be covered in a future blog post.