Runtime services are distinct pieces of logic that run in the background of the workflow runtime and can provide behavior key to the workflow infrastructure or maintenance tasks.
Several service types included in the base API are provided as out-of-the-box services, including scheduling, work batch, persistence, tracking, workflow loader, and data exchange services. Several of these service types are so important to the functionality of the workflow runtime that there are default services that are used if no other services of that type are specified.
In addition, you can develop workflow runtime services to provide custom logic. This can occur by deriving from one of the base workflow service types in the API or by developing an entirely new service type from scratch.