Fedora 4 provides many options for developing event-driven architectures around the core system.
HTTP APIs
At the HTTP level, Fedora 4 has two optional components, RSS feeds (pull) and Webhooks (push).
Webhooks
fcrepo-webhooks is an optional module. Webhooks allows you to register a callback url as a lightweight means of acting on repository events. The callback url will receive a POST request when an event is triggered with information about the event that triggered it.
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fcrepo-kitchen-sink includes fcrepo-webhooks (along with all the other optional modules).
RSS
fcrepo-rss is an optional module that publishes a list of recent events.
fcrepo-kitchen-sink includes fcrepo-rss (along with all the other optional modules).
Message Queues
Fedora 4 can publish events on a JMS message queue.
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Modeshape also has some tightly-integrated asynchronous operation machinery called Sequencers.
ModeShape sequencers can automatically unlock the structured information buried within all of those files, and this useful content derived from your files is then stored back in the repository.