a workflow need to be started or triggered when the content metadata inside the oracle content server meets some criteria like 1.release date = system date or 2.author="xxx". when the criteria meets it should automatically start workflow.
here you can find a documentation how you can create a own agent. http://download.oracle.com/docs/html/A96698_01/servers.htm#1036819. The example is based on cmsdk version 9.0.3 but it should also work with content db. I don't know at this point if Oracle supports custom agents with content db.
Also note, that content db is shipped with a set of agents (http://download-west.oracle.com/docs/cd/B32119_01/doc/contentdb.1012/b31268/serverconfig.htm#g667975)