After Twitter started announcing changes to its API usage and people started to get worried about the future of the developer eco-system, App.net appeared. It provides a streaming data-platform in much the same way Amazon provides a web hosting platform. The reason for the Twitter comparison is that one of the things you can make with it is a Twitter-like public short message system. This was, in fact, the first thing the App.net developers made to showcase the platform: Alpha although that example seems to have convinced many people that the whole point was to build a Twitter-clone instead of a service whose purpose is to stream small, discrete blocks of meta-tagged data. The community-developed API spec is an important aspect of App.net as well although feature discussions can devolve into musings on Computer Science theory a bit too easily.

For the first couple of weeks, it was fun to just hack around with the APIs, post a bit, build a little test app (disabled now that more App.net clients have push notifications). It all became much more interesting, however, when two new features were added to the platform ā€“ Machine-only posts and Well-known Annotations.

Machine-only posts

Pretty much exactly what they sound like. These are posts that are not intended to be viewed in any human-read conversation stream. They still get pushed around the network exactly the same as all other posts but to see them, you must explicitly say 'include machine-only posts' in your API calls. For developers who have been building silly toys on Twitter for a couple of years, this is fantastic. You don't need to create a separate account purely for data transfer. This can be part of your main account's data stream. I have quite a few Twitter accounts that I just use for outputs from various applications. I have one, in fact, that does nothing but list the tracks I listen to that I created for this side-project.

By classifying these as 'machine-only', they can stay associated with the user and subject to whatever privacy controls they have set in general. This makes it far easier for the user to keep control of their data and easier for the service to track accurate usage. For devs, it also means you can hack away at stuff, even if it is to be public eventually, without worrying too much about polluting the global stream with nonsense.

Well-known Annotations

Annotations were part of the spec from the beginning but only implemented at the end of August. Annotation is just another word for per-post meta-data ā€“ each post has a small object attached which provides extra information. That's it.

The annotations can be up to 8192 bytes of valid JSON which is quite a lot of meta-data. Even with this, however, the usefulness is limited to per application use-cases until some standards start to appear. There's nothing to stop a popular application being the one to set the standard but for the more general cases, it is most fitting to continue with the community-led development model. This is where Well-known Annotations come in.

Well-known annotations are those attributes which are defined within the API spec. This means that the community can define a standard for 'geolocation', for example, and everyone who wants to use geolocation can use the standard to make their application's posts compatible with everybody else's.

Obviously, I'm quite into my geolocated data. I love a bit of map-based visualisation, I do. Here's a sample of jQuery that will create a post with a standard geolocation annotation:

$.ajax({
  contentType: 'application/json',
  data: JSON.stringify({
    "annotations": [{
      "type": "net.app.core.geolocation",
      "value": {
        "latitude": 52.5,
        "longitude": 13.3,
        "altitude": 0,
        "horizontal_accuracy": 100,
        "vertical_accuracy": 100
      }
    }],
    machine_only: true
  }),
  dataType: 'json',
  success: function(data) {
    console.log("Non-text message posted");
  },
  error: function() {
    console.log("Non-text message failed");
  },
  processData: false,
  type: 'POST',
  url: 'https://alpha-api.app.net/stream/0/posts?access_token=USERS_OAUTH_TOKEN'
});

In the same way as the machine-only posts, these annotations aren't provided on a default API request, you have to specifically ask for them to be included in the returned data. This is to make sure that the majority of use cases (public streaming, human-readable conversation) don't have to download up to 8KB of unnecessary data.

Retrieving both

This is an API call to retrieve posts marked machine-only and with annotations

Potential use cases

You might have noticed, the API call above had the machine-only attribute as well as the well-known geo annotation. If I wanted to create an app that would run on my phone and track my routes throughout the day, all I would need to do would be to run that $.ajax call periodically with my current geolocation. The data would be saved, distributed, streamed and could be rendered onto a map or into a KML at the end of the day. I could record hiking trails or museum tours, or share my location with someone I'm supposed to be meeting so they can find out where I'm coming from and why I'm late. That's just a couple of the single-user cases. Having a shared standard means that the potential for geo-tagged posts opens up to at least equal that of Twitter's. Heatmap-density diagrams showing areas of the most activity; global and local trends; location-based gaming. Add a 'news' annotation to geotagged posts and suddenly you've got a real-time local-news feed. Add 'traffic' and you've got community-created traffic reports.

There are so many clever things you can do with location-tagged data. I hope others are just as enthused about the possibilities as I am.