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Thanks for taking the time to study PubSub.com and provide your comments. I would, however, like to point out a few inaccuracies in your note:
1. You understate PubSub's throughput capacity by three orders of magnitude! We benchmark at 3 billion matches per second -- not the mere 2.4 million/second that you claim! If PubSub could only handle a few million matches per second, PubSub wouldn't be a very useful system. An Internet Scale system must be able to handle millions of complex subscriptions that are each being matched against at least hundreds of messages per second. Matching rates of billions per second are a *minimal* requirement for Internet Scale matching engines.
2. In addition to providing notifications via "Atom over XMPP/Jabber", RSS and Atom files, PubSub also supports email notification for SEC Edgar alerts, press releases, and Airport Alerts. (We don't support email for Weblog or Newsgroup updates simply because volumes could too easily become excessive for users.)
3. PubSub does support "REST" notifications -- i.e. Atom entries which are POSTed using pure HTTP. However, we have found no interest in the community for using these things (primarily because they can't punch through firewalls) and thus have given up on publicizing our REST support. We continue to support those few people who have been using these REST alerts, but don't anticipate finding many new users. Note: We also implemented SOAP based notification but couldn't find anyone interested in even testing it. Notifications are most valuable when they reach to the desktop (not just to servers) but the desktop is typically shielded by firewalls.
4. It is odd that you suggest that PubSub is not a "generalized" pubsub system. Actually, that is precisely what we have built. However, at this time, we only choose to expose the specific applications that we have built using our very generalized system. The money is in the applications -- not tools or technologies. We'll provide access to the general system later but need to focus on the applications for now.
5. Your suggestion that PubSub eliminate the "two step" subscription process of 1) Specify subscription query and 2) receive result URI, ignores a number of important elements of our service. First, doing what you suggest would require that no subscription could be more complex then what can be packed into a limited-size URI. This is a significant restriction. We support general boolean queries with potentialy dozens of terms or predicates. A subscription can easily become much larger than what can be stored in a URI. Also, to rely on a user provided URI would require that user-specific information be included in the URI. That would make it impossible for users to "share" the URI's for the subscriptions they generate.
Thanks again for taking the time to review what we've done. If you have any more ideas on how we might improve our service, please let me know.
bob wyman
CTO, PubSub.com
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