At the Forge: Bloglines Web Services
Another offering from Bloglines, as we mentioned earlier, is the Blogroll API. A blogroll is a list of Weblogs that a particular author finds interesting and often reads. It's likely that if you enjoy reading someone's Weblog, you also would enjoy perusing that person's reading list. In the case of Bloglines, a blogroll simply is a list of subscriptions associated with a particular user.
So far, we have mentioned that someone's Bloglines user name is the same as his or her e-mail address. But this is not completely true—if you choose to use Bloglines for your own private purposes, never sharing information about your subscriptions with other people, you need nothing more than your e-mail address. But if you do want to expose your subscriptions, you must choose a user name with which they can be associated. In my case, my registration e-mail address is email@example.com and my user name is reuven. This distinction wasn't clear to me for the first few months that I used Bloglines, although it seems to be more obviously advertised now.
But the whole idea of Web services is to make data machine-readable, such that it can be stored and processed by computers. OPML, the Outline Processor Markup Language, specified by Dave Winer in 2000, is the format used by Bloglines when it exports a list of subscriptions. It is not an official part of the Bloglines Web services specification, but you can retrieve it by going to the following type of URL: http://www.bloglines.com/export?id=reuven.
In all of the above examples, you can and should replace my Bloglines user name with that of the user whose blogroll you want to read. Not every user makes his or her subscription list public, so you may encounter error messages when trying to retrieve them. And once you retrieve the OPML, you need to process it, perhaps using a tool such as the publicly available XML::OPML module from CPAN.
As you can see, the Bloglines API for Web services opens the door to a host of third-party applications. It increasingly is possible to create useful applications that use HTML, XML and HTTP but that are not tied to a Web browser. The Notifier and Blogroll APIs are only the beginning. As we saw earlier, there is also a Sync API that effectively allows developers to create alternative GUIs and applications with the actual content Bloglines retrieves and stores. In my next column, we will look at the Sync API, building some basic applications on top of the Bloglines infrastructure.