When searching/fetching items through the EUtils interface to PubMed, you can specify an 'earliest' date (the mindate parameter), meaning that it's easy to fetch all the items added since a particular time. This is a feature missing from most feed providers: all you can get, generally, is the last n items. This is ok if you're fetching items from a blog where you can poll about once a day and be reasonably sure that there won't be more than 10 or 20 new items posted in that timeframe, so you won't miss anything. However, it breaks down with feeds coming from last.fm or del.icio.us, for example, because there could easily be more than 20 new items added since you last requested the feed. Also, it's not possible to use the feed to fetch any further back in the archive. There's RFC 3229: Delta encoding in HTTP, which was discussed (and implemented) by Bob Wyman and others in 2004. When the client asks for data, it includes the ETag of the latest item it holds (and an A-IM header) in the request and the server Read More... |
