Publish and Subscribe (was: Re: Some suggestions for RSS .92)

[Aaron Swartz <aswartz@swartzfam.com>]

Dave Winer <dave@userland.com> wrote:

> I also want to work out a simple XML-RPC/SOAP integration, I want to make a
> channel subscribable, so that the publisher calls the subscriber when
> there's an update.

Me and Dan Lyke have been doing some work on this area, with the changedPage
spec. Here's what I wrote to him:

First, I think the spec should be broken into two parts. The first being the
client-side part, which notifies a client of a URI being changed (this is
the heart of the spec). The second is more of the server-side part, which
deals with subscription, unsubscription and discovery of these changedPage
feeds.

For the first part, XML-RPC might be overkill. Instead, one might want to
just send a normal post request, with the URL as the content of a URL
variable. This is very simple, and likely more widely supported than
XML-RPC. Also, since no complicated XML parsing needs to be done, it's
likely much faster and less processor intensive.

It also results in much smaller file sizes -- instead of a big large
complicated XML file, it's simply a short line like:

url=http%3A%2F%2Fwww.theinfo.org%2F

It also is forwards-compatible (at least in most implementations). If we
want to add more values, we just append them on:

url=http%3A%2F%2Fwww.theinfo.org%2F&specialkeyword=woohoo

Whereas with an XML-RPC, adding additional values on to the end breaks
compatibility with some implementations.

For the second part, XML-RPC might be reasonable, but a normal Web interface
would be too, as well SOAP and any other format we can come up with.
Meanwhile, the core of the spec is based on HTTP, which is about as webby as
you can get. This will likely help adoption, especially since it's not laden
with the complexity and politics of XML, etc.

Thoughts?

-- 
        Aaron Swartz         |"This information is top security.
<http://swartzfam.com/aaron/>|     When you have read it, destroy yourself."
  <http://www.theinfo.org/>  |             - Marshall McLuhan