WorkflowDefinition
    graph      (WorkflowGraph FileId)
    initiator  (WorkflowRole UserId AuthDNF)

WorkflowInitiator
    -- TODO descriptor of a "role" that can initiate an instance of a workflow in a specified scope

WorkflowInstance
    definition  WorkflowDefinition
    initiator   (WorkflowRole UserId AuthDNF)

Workflow
    instance    WorkflowInstance
    initiator   UserId