By "orchestration" I'm assuming you mean a finite state machine. Where the current state dictates what transitions can be followed to other states. The representation of states and transitions as edges and vertices often produces a directed acyclic graph, however there are times when the graph will cycle (e.g. draft -- submit for approval --> pending approval -- reject --> draft).
In practice, separating the definition from execution calls for a persistence format that can easily accommodate customization. As your system evolves you will find a number of unanticipated edge cases whose solution should not require altering a persistence schema, only code. This implies XML or a NoSQL solution - something whose schema is easily changed or non existent.
Now, having written my own XML definition for this purpose (for uninteresting reasons I'll exclude), my suggestion is using JPDL (or BPMN). Reason is their definitions likely incorporate whatever you're considering now, will in the future, and enable customization - such as hanging arbitrary data or behavior off them at a given point. You also get the advantage of tools already built - not just UI - for dealing with cycle detection and ensuring there is a path to completion for example.
Some of the interesting features I know JPDL possesses are an ability to help merge forked processes, timed tasks (including those that repeat periodically), and facilities for sending notification. This last item - notification - bears some further exposition. One of the things I've found with my own system is the need for sending out configurable email whose content is based on the data flowing through. These existing engines make that relatively easy by providing a way to plugin variables for instance into text that's then dynamically evaluated at run time before transmission. Also they provide bridges between the engine and whatever user store for the purpose of sending notifications to groups of people, tasking them and enforcing security policy.
Finally, depending on the scope of your system, you will probably still be using a database as well. What I suggest is storing off the XML and data being orchestrated into the database in a serialized format. Then, if the data is being altered as it travels through the execution, write out serializations of the data - and perhaps workflow if it is also changed - into a history/audit log table as well.
