Catch is often thought of as an Evernote competitor, thanks to the company’s simple, note-taking applications for iOS and Android. But more recently, the company’s APIs were found integrated into a high-profile mobile application: Google’s official app for its I/O developer conference. In the Google I/O app, Catch was used to help attendees create and manage conference notes using the Catch service.

As it turns out, there are today over 40 apps using Catch’s APIs, including those from the BBC and TED, plus recipes and horoscopes apps and others. And now, with Catch’s newly launched annotations API and its support for structured data, Catch can enable different mobile apps to talk to each other.

Prior to the release of Catch’s annotations API, the service supported only text, location, photos and voice in its notes. But sometimes, explains Catch CTO Andreas Schobel, you want to add structured data, too.

Developers can now do just that by registering new annotation types with Catch. For now, this is done by sending emails to developer@catch.com. Soon, a self-service registration page will be available to make the process even easier.

According to the Catch developer site, the annotations types currently have the following properties:

  • namespace: A grouping for common annotations, generally relates to the application that uses them (health tracker).
  • key: The key for the particular annotation.
  • id: The id of the annotation type is composed of the namespace and key as namespace:key. The id is used for manipulating annotations in the Notes API.
  • unique: Whether the annotation can have multiple values per note.
  • processor: The method by which annotation values are processed. Built in processors are string, boolean, and number. Numbers have built in unit conversion.

So how does this annotations API allow apps to talk to each other? Well, for example, instead of having a note field in an app where you recorded your weight daily as text, that information could be saved as data. Then a second app could read that data. In the weight-tracking example, the second app could translate pounds to kilograms, for instance, or it could correlate your weight with your daily blood pressure readings, which the second app provided.

Another basic example of annotations are the starred notes Catch implemented into its own note-taking apps recently, which allows users to save their favorite notes.

These are very simple examples, of course, but the possibilities of annotations made available via API are interesting, especially in terms of sharing data between different applications – even those from different developers.

Catch provides three different ways to leverage its service – via an HTTPS REST API, open-source libraries or through Android Intents. Interested developers can learn more about Catch at developer.catch.com.