Events

REST in Practice Tutorials, Sept-Oct

August 27th, 2010  |  Published in Events, REST by Ian Robinson

Over the next couple of months, Jim Webber and I will be running several day-long REST tutorials:

  • Following JavaZone, we’ll be at Oslo’s Henning Solberg on Friday, 10th September. You can register for JavaZone here, and for the tutorial here.
  • At the beginning of October, we’re at the wonderful JAOO Aarhus, with the tutorial running throughout the day on Friday 8th October. Register here, with a 20% discount if you use the JAOOspeakerfollower promo code.
  • Closer to home, we’ll be at Software Architect 2010 in London on Friday, 22nd October. You can register for the conference and tutorial here.

The tutorial agenda closely follows the structure of REST in Practice, which hits the shelves on Sept 24th:

  • The Web Architecture: HTTP and URIs
  • The Richardson Maturity Model
  • CRUD Services using URI templates and HTTP
  • Hypermedia and the REST architectural style
  • Implementing domain application protocols
  • Atom- and AtomPub-based event-driven systems
  • Scalability through caching
  • Semantics using Microformats and RDF
  • Security and the -ilities

With ThoughtWorks recently having opened an office in Germany, I’ll also be presenting at Herbstcampus in Nuremberg, 12-15th October.

And finally, if your want to enjoy some REST in Practice from the comfort of your own office (or home), there’s still time to sign up for the ThoughtWorks’ Webinar, Designing and Implementing RESTful Application Protocols, which takes place on Wednesday, 1st September, at 6.30pm IST (that’s, er, sometime in the afternoon GMT).

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WS-REST 2010 Proceedings

April 28th, 2010  |  Published in Events, REST by Ian Robinson

The preliminary proceedings for WS-REST 2010 are now available online. Thanks to Cesare Pautasso, Erik Wilde, and Alexandros Marinos for organising what proved to be a very engaging and wide-ranging workshop; and to Guilherme Silveira, who – much to my amusement – 20 minutes before the workshop started wrote the Restfulie implementation to accompany the paper that we were there to present. The slides for this paper, which was written by Savas, Jim, Guilherme and me, can be downloaded here.

I understand that someone recorded the panel session at the end of the day: I’ll post details as soon as the recording becomes available.

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The Counterintuitive Web

March 15th, 2010  |  Published in Events, REST by Ian Robinson

The slides from last week’s talk at QCon, The Counterintuitive Web, are now available online.

In the talk I described how we can implement rich and interesting business processes in (RESTful) Web applications, but only if we think in terms of protocol resources, not coarse-grained domain resources. By embracing the Web as first and foremost a web of data, an open set of resource representations manipulated in the same-old-same-old ways using a closed set of verbs, our designs capture the behaviours most CRUD-based, data-centric applications so sorely lack.

Many thanks to Dan North for inviting me to speak on his Irresponsible Architectures and Unusual Architects track.

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London Geek Night

February 12th, 2010  |  Published in Events, REST by Ian Robinson

Updated The video of Thursday’s London Geek Night is now online. Thanks to Ikenna Okpala and Skills Matter for recording the event.

Thank you to everyone who came along to the London Geek Night last night. There were many good questions and comments throughout the evening. I didn’t respond to all of them satisfactorily at the time, so I thought I’d expand on a few of them here.

Enforcing the protocol

Alex Scordellis asked a very challenging question: how does the server prevent the client from “teleporting” to locations that aren’t immediately accessible from its current location? In other words, how do we stop the client jumping around the app, ignoring the advertised URIs, going off the rails, and interacting with resources in a way that contravenes the application protocol?

One solution to this problem is to use ephemeral URIs. Remember, other than the entry point URI, every URI the client encounters will have been minted by the server as it generates representations. By appending an expiry time, signed using a private key held only by the server, to each URI, we can ensure that each URI the client is given is valid only for a short period of time. Subbu Allamaraju and Mike Amundsen talk about ephemeral URIs in their forthcoming book, RESTful Web Services Cookbook. Amazon S3 offers the capability to sign URIs in just this fashion so as to limit access to resources.

Of course, this still leaves a short “teleport” window open, which the client can use to make multiple requests of a resource that it ought no longer access. To close this window, we might consider maintaining a secret resource access counter per ephemeral URI inside the server implementation. When the counter limit is reached, the server replies with 204 No Content. The only way for the client to access this resource again would be for it to play fair by the application protocol, navigating advertised transitions until it comes upon a representation containing a link (with new ephemeral URI) to the desired resource.

It can be argued that a GET that increments a secret counter associated with a resource (at an ephemeral URI) is no longer safe. Is the incrementing of a secret counter an unintended user-visible side-effect? The argument is played out in the comments to a post from Sam Ruby from 2002. Read the comments here and make up your own mind.

Resource design

Adewale Oshineye asked how a design ought accommodate making small changes to large resources – is this necessarily an inefficient operation that requires the client to PUT the entire representation back? He also asked how one might support large batch operations in an efficient manner.

HTTP PATCH supplies one mechanism for dealing with partial updates, which fall under Adewale’s first question. Taken together, however, I feel Adewale’s questions lead us to reflect on the role of resource design in the overall design and implementation of a RESTful application. If we model our resources based simply on an understanding of business resources, we can end up with a resource landscape that’s not amenable to being manipulate din the way we require.

The first piece of advice usually given a would-be service designer is: identify your resources and assign them URIs. But this can all too easily lead us to identify only business resources – customer, product, order, etc – and equate these business resources with the resources our service exposes. But remember, the resources we deal with on the Web are information resources, which are somewhat more abstract than the business resources we typically capture in a domain model.

The design and implementation strategy that Jim, Savas and I recommend in REST in Practice is:

  1. Design applications in terms of application protocol state machines
  2. Implement them in terms of resource lifecycles
  3. Advertise/document them using media types, link relation values and HTTP idioms

The transition from 1. to 2. here requires the service designer to decompose an application protocol into whatever information resources and information resource lifecycles are necessary to realise the protocol. The kinds of resources you identify using this approach may look a little different from the ones you would have identified had you taken a business domain resource approach.

I’m being a little vague here, but it’s a subject I plan to develop in more detail at QCon London.

And finally…

In other comments, Bruce Durling pointed out I was mixing up 3rd edition D&D and 1st edition AD&D rules. Guilty as charged. -1 Credibility, no saving throw.

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Hydras and Hypermedia at London Geek Night

January 28th, 2010  |  Published in Events, REST by Ian Robinson

On February 11th I’ll be presenting Hydras and Hypermedia at London Geek Night.

Do you know what your enterprise apps get up to in their time off? Fighting fantasy, pick-your-path, hypermedia-driven, RESTful Web application adventures – of course.

In this speculative dungeon delve I’ll show how we can use hypermedia-driven Web applications to model rich workflows. We’ll tackle the many-headed Hydra of HATEOAS, the “Hypermedia as the Engine of Application State” monster; level up through the Web services maturity heuristic; and meet the dwarves with grudges. On the way, we’ll learn how to model business processes as domain application protocols, implement them in terms of resource lifecycles, and advertise them using HTTP idioms, media types and link relation values.

Event
London Geek Night
Description
Hydras and Hypermedia
Date
11th February
Time
7 pm10 pm
Location
ThoughtWorks UK Office

Berkshire House
168-173 High Holborn
London
WC1V 7AA

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