Guido Casper wrote:
Stefano Mazzocchi wrote:
If FSM work bad for flow, why would they work any better for workflow?
After thinking again about ways to use continuations with workflow I came to the conclusion this might well be possible. But it looks awkward to me.
Each document attached to workflow would need a workflow instance as long as the document lives (from creation to deletion). This would mean the continuation stack of every document needs to be persisted to - well - to a database if you don't want to limit your clustering options. The document has a property holding the continuation ID.
You have a point here, Guido. It is true that continuations in a distributed environment would need to be made custer-friendly and replicated. This would probably impact the overall performance... but keep in mind that continuations are just another way to save state. That kind of state transformation (think REST) will have to be done anyway.
The lifetime of a workflow instance also makes a big difference regarding business process changes. I experienced in a previous job in a large company some workflows (e.g. purchase orders) who changed several times a year, depending on structural changes in the company's organization. And already running instances had to adapt to the new worflow from the state they were in at the date of workflow change.
This makes continuations technically not suitable for this, as once a continuation has been created, it's tied to the program's structure where it was created, and it cannot be "rerouted" to a location in another version of the same program.
Furthermore, there exists what is called "ad-hoc" worklows, where a user, depending on its rights, can modify the workflow for a particular instance. An example of this is when a document has to be published that contains highly technical material. The editor may want to add an additional step in the workflow for the document to be validated by a technical expert, which doesn't happen in normal cases.
In that situation, asking a user to write a new version of a program for that specific need doesn't seem a good solution to me ;-)
Sylvain
-- Sylvain Wallez Anyware Technologies http://www.apache.org/~sylvain http://www.anyware-tech.com { XML, Java, Cocoon, OpenSource }*{ Training, Consulting, Projects }
