Monday, September 17, 2007

GData AtomPub Podcast

I just listened to The world of Google data APIs. It is 42 minutes long. I took notes.

Here is the agenda:

  • What "Google data API" actually means (the parts and pieces)
  • What Atom, Atom Publishing Protocol, and other tech behind GData are all about
  • What GData adds to the mix on top of Atom and APP
  • How Atom compares to RSS
  • What are ETags? And how can they help me?
  • Why REST, the style, was chosen for these APIs
  • Where REST makes sense, and where it doesn't. Resource driven vs. RPC.
  • What the first GData APIs were
  • How the killer app of syncing data with Google Calendar
  • How you actually use the APIs? What do they need to learn? What tools do we give them?
  • Can you write APIs that implement the same GData APIs?

Notes: Atom is an IETF standard in case you didn't know. RSS isn't.

Google has been working with Atom for over 2 years.

AtomPub provides a basic REST API - Google thought this was a great starting point. Atom leaves query to the student. Google uses URLs to do this. You can have output sorted etc. Atom doesn't say anything about this.

ETags were unfortunately not implemented. They chose a version number in the URL so that multiple people can write to the same entry. Plan to implement ETags in the future.

Are ETags magic? No, a lot simpler than they sound. A little string that tells you the version of the entry. Just a great way of making caching work & making the web more efficient.

Chose Atom because of momentum. And sold on REST. Not SOAP because the web is based on REST. Much easier for devs to learn REST than SOAP. SOAP require tooling. REST is simply manipulating tables of entries.

What are disadvantages of REST? AtomPub is just an implementation of the REST style. Difficult to map certain types of operations to REST - translation API example: send text & send back a list of options & then feedback how to improve the translations. Document centric request / response that was never saved on the server. Just a straight RPC call. REST is about manipulating resources.

How about transactions? Each request is essentially transactional. REST not concerned with multi-resource transactions.

How do devs use? Can use curl if they want to - some do create apps with shell scripts and curl. Have a Java, .NET, PHP, Python, Objective C API. Contributed APIs: Lisp (Patrick!), Ruby, Flash in development. It's just XML over HTTP - it's NOT THAT HARD!!

Authentication - "Client Login" is pretty straight forward auth. URL for uname/passwd where you get a token back that is your identity. Authentication for Web Apps - "Auth Sub" used for "on behalf of" type stuff. You can grant access to other web sites. You control who has access to.

Can I use Google Auth? They are meant to be open standards. Google legal hasn't signed off yet, but licensing will be worked out soon.

What is this "Kinds" business? Entries get passed around a lot - kinds concept is Atom categories to tag each entry with a "kind". Just gives more semantic information to computers (clients).

AtomPub Google Interop Event? 12 devs from different orgs came. Great success. Google's basic AtomPub worked fine. Google custom auth scheme was more problematic. After that everything worked smoothly. A lot of the impls built around AtomPub introspection document - Google doesn't use them much. Will in the future.

Any GData / AtomPub tips? Google has a particular approach to designing APIs. AtomPub good at certain APIs. Things that map well - RPC not one of them. On occassion Atom Entry is just a pointer to the real data (e.g., photos). Prefer to put data in entry as much as possible. There is a lot of art/style/parsimony to it. You can achieve a lot with 1 feed with a lot of query parms. Have to review APIs & ensure that they have good clean concepts: this feed clearly includes these types of elements.

WADL? Haven't found the need for it.

Atom can be tough to get at first, but once you do it is amazingly simple & then applicable to many. Very good programmers who don't understand AtomPub gargen/language can. Concepts are very simple. Feeds, entries, links to other entries. Very simple mental model once you get it. All APIs make the same. Very powerful.

Google working with the IETF on improving Atom/AtomPub. Introduced batch model that increases efficiency a lot. Auth. Teams in Google are very ambitious - hope to make publically available as drafts that can become standards.

Some talk of JAY-SAHN (JSON).

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