You don't need to create schemas for tasks, they come out automatically. At least, that's how I see things. Each square in that diagram is a 'state'. Thats about it. Next, you have the arrows, which connect the states.
States are the stages which a 'document' flows through during a process.
The document gets routed from desk to desk, gaining signatures, and getting notes stapled to it. Notes have a date attached. Some notes might by cryptographically signed with electronic signatures, etc. Some notes may contain embedded images, embedded html, or references to other documents. Next, you have permissions.