Google didn't waste any time giving developers a chance to dig right into their new appointment-tracking service. Google Calendar, a tie-in to Google's GMail service, was launched in mid-April. Within a week, Java and .NET APIs were released to enable developers to write applications to programmatically and easily interact with the service. Likewise, for those who prefer working with raw XML, Google's GData API, a blend of Atom and RSS feeds, enables direct interaction without overhead.

In this article, we take a quick look at the raw GData interface, then dig into the .NET flavor of the Google Calendar Data API, and finally look at an example that interacts both with Outlook and Google.

GData — Google's Data APIs

As part of their plan to take over the world (in a good way), Google has created what they call GData, a collective term for referring to a variety of Google-related APIs. The GData API is built on two XML standards: Atom and RSS. Neither of these two support the full suite of features that Google was looking for to exchange all the various types of information needed for the various Google applications, but the two combined do the trick.

GData enables the request and deliver of data encapsulated in a simple XML format. Data is retrieved via feeds provided at standard URLs (www.google.com/calendar/feeds, for example), and is provided by sending POSTs containing XML-encrypted messages along with the necessary authentication token. Authentication is achieved by sending a separate POST to https://www.google.com/accounts/ClientLogin containing the e-mail address and password of the account that will be receiving the data, along with information about the application making the call and the service being requested.

Like most Atom APIs (and, as in this case, Atom-related APIs) the GData API isn't too difficult to work with in straight XML. However, interacting with a code library makes for much faster development and much easier debugging than sending and receiving straight XML messages. We focus on the .NET flavor of the Google Calendar Data API, but the Java version is similar, and for the most part, the concepts here apply to interacting directly with the GData interface in XML.

Both Java and .NET libraries can be downloaded at from Google here.