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From "Brett Gullan" <>
Subject Workflow & Turbine design questions
Date Wed, 28 Nov 2001 03:11:07 GMT

I am working on a project to develop a Turbine-based workflow engine for
file processing, using the Commons Workflow package and I would be
interested in any feedback or suggestions as to how best to implement
The main focus of the project is to automate file processing for
print/publishing workflow. Users move/copy files into predefined
"hotfolders" which trigger a series of workflow steps such as converting
a file from PostScript to PDF, compressing images or transferring a file
or directory to a remote server (via FTP, HTTP, WebDAV, etc...).
Currently I have created a WorkflowService, modelled after the Turbine
SchedulerService that retrieves items from a queue and initiates the
processing sequence. A scheduled job periodically retrieves the list of
hotfolders (from storage; they are implemented as OM/Peers), checks for
any new files and submits them to the workflow queue, along with a
reference to an Activity definition that will be used to process the
My intention is that as each entry is retrieved from the queue the
associated Activity definition file is 'digested' and a processing
thread started to perform the workflow steps.
I also need to ensure there is a mechanism for maintaining
state/progress information for each workflow step -- both to report back
to the client UI and for 'recovery' should a process be interrupted.
Workflow steps may be quite expensive and/or time consuming -- for
instance, PDF conversion of large publishing files typically takes 1-5
minutes, thus processing a directory of files could take significantly
longer. During this period a user needs to see progress information such
as a progress bar or estimated time to completion.
I am unclear at this stage as to how the workflow Context and Scope fit
in. I figure the processing thread itself should probably be a Context
implementation and maybe the Scope implementation is the conduit to the
UI? A Velocity Screen/Action could request a list of processing
threads/Contexts from the WorkflowService and insert each Scope
implementation into the Velocity Context? The Scope would probably also
need to be backed by an OM/Peer to persist state information.
I would appreciate any suggestions or alternative design ideas.

Brett Gullan

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