Home > Archive >  2009 >  July >  10

A more low-tech approach to ping hubs

Friday, July 10, 2009 by Dave Winer.

When talking with the Google guys earlier today I told them that there was an even more low-tech approach than the <cloud> element for the kind of notification they were doing. As I was reading their spec, I decided to look into it to refresh my memory. I'm writing it up here, so everyone can compare. 

1. Unlike <cloud> this protocol was very widely implemented. Support for this protocol is already baked into almost all blogging software, and (likely) many CMSes.  

2. The feed indicates which hub it belongs to using a <category> element. You can see an example looking in the feed for my Radio weblog. I've made a copy of that feed in case the link goes bad (I hear that Radio weblog hosting may end in December.) 

This means that if you want to find out if this feed changed, you should monitor the indicated changes.xml file. 

3. When the feed updates, it pings the server that maintains that changes.xml file. The coupling here is much looser than the coupling that Google is using. But the changes.xml file can be read once a minute. If your application can handle up-to-the-minute updates instead of up-to-the-second, then this approach works fine.