Control needed to be able to only notify a subscriber of an update in the topic IF the subscriber has permission to read the document that updated
Amazon SNS will NOT allow that level of control
PubSubHubbub will allow this if using a custom implementation of the protocol
Don't want to send actual content with notifications, just a notification message
PubSubHubbub will allow this if using a custom implementation of the protocol since most existing implementations want Atom or RSS content and will send updated portions of the content with notifications
Topics that can be subscribed to will not be document URLs, but search-based endpoints that are collections of documents:
Search will need a way to target documents that are associated with these topics
Just add an index field for the topic?
Also include the field in the document itself?
Custom notification server will need
to comply with PubSubHubbub protocol so that existing clients still work
an endpoint/URL where subcribers can subscribe/unsubscribe
a storage mechanism for keeping subscriber callback URLs for a topic