This will be a very hands-on tutorial. Over the course of three and a half hours we’ll build a hypermedia-driven service and client in .NET using the new WCF Web APIs. The subject matter hearkens back to a favourite subject of mine, Hydras and Hypermedia, for the application we’ll build will be a simple text-based pick-your-path-to-adventure game.

This isn’t a tutorial on games design, however. Despite the non-enterprisey subject matter, the tutorial serves to illustrate how machine clients and services can cooperate to achieve a useful application goal. Business application analogies lurk around every corner and surprise you with every encounter.

The tutorial comprises three exercises. With each exercise you’ll have to fix a number of broken unit and functional tests. Bit by bit, you’ll build a working application:

• Exercise 1: Here we implement the server resources that make up the dungeon – the chambers, tunnels and caves in which our daring client will venture.
• Exercise 2: Next we build a crafty client that can discover a path through the dungeon. By the end of the exercise, the client ought to be able to navigate the dungeon from entrance to exit.
• Exercise 3: Last, we add an element of danger, populating the dungeon with encounters (more resources) that the client must overcome before it achieves its application goal.

Along the way you’ll learn about:

• The Atom Syndication Format
• “What if” client-side intelligence
• The client as arbiter of application state
• Hypermedia controls: links, link relations and forms
• DRY URIs

So come and join me for what promises to be an entertaining hack-n-slash workshop. Attendees should be familiar with C# and unit testing, and have some knowledge of HTTP.

Full details and registration for the entire event can be found here.

I’ll be building on some of this material at QCon London (March 9-11), but there I’ll go deeper into some implementation specifics, with examples drawn from some recent work with Microsoft’s new WCF HTTP libraries. (The QCon REST track has a particularly stunning lineup.) Also as part of QCon London, Jim Webber and I will be running our day-long REST in Practice tutorial.

You can register for QCon here. When doing so, use the ROBI100 promotional code. This gives you a £100 discount; at the same time, QCon will donate £100 to the Crisis Charity in London (the national charity for single homeless people).

Background

Over the past few years, several discussions between advocates of the two major architectural styles for designing and implementing Web services (the RPC/ESB-oriented approach and the resource-oriented approach) have been mainly held outside of the research and academic community, within dedicated mailing lists, forums and practitioner communities. The RESTful approach to Web services has also received a significant amount of attention from industry as indicated by the numerous technical books being published on the topic.

This second edition of WS-REST, co-located with the WWW2011 conference, aims at providing an academic forum for discussing current emerging research topics centered around the application of REST, as well as advanced application scenarios for building large scale distributed systems.

In addition to presentations on novel applications of RESTful Web services technologies, the workshop program will also include discussions on the limits of the applicability of the REST architectural style, as well as recent advances in research that aim at tackling new problems that may require to extend the basic REST architectural style. The organizers are seeking novel and original, high quality paper submissions on research contributions focusing on the following topics:

• Applications of the REST architectural style to novel domains
• Design Patterns and Anti-Patterns for RESTful services
• RESTful service composition
• Inverted REST (REST for push events)
• Integration of Pub/Sub with REST
• Performance and QoS Evaluations of RESTful services
• REST compliant transaction models
• Mashups
• Frameworks and toolkits for RESTful service implementations
• Frameworks and toolkits for RESTful service consumption
• Modeling RESTful services
• Resource Design and Granularity
• Evolution of RESTful services
• Versioning and Extension of REST APIs
• HTTP extensions and replacements
• REST compliant protocols beyond HTTP
• Multi-Protocol REST (REST architectures across protocols)

All workshop papers are peer-reviewed and accepted papers will be published as part of the ACM Digital Library. Two kinds of contributions are sought: short position papers (not to exceed 4 pages in ACM style format) describing particular challenges or experiences relevant to the scope of the workshop, and full research papers (not to exceed 8 pages in the ACM style format) describing novel solutions to relevant problems. Technology demonstrations are particularly welcome, and we encourage authors to focus on lessons learned rather than describing an implementation.

Papers must be submitted electronically in PDF format. Templates are available here

Easychair page: http://www.easychair.org/conferences/?conf=wsrest2011

Important Dates

• Submission deadline: January 31, 2011, 23.59 local time in San Francisco, CA
• Notification of acceptance: February 15, 2011
• Camera-ready versions of accepted papers: February 28, 2011
• WS-REST 2011 Workshop: March 28, 2011

Program Committee Chairs

• Cesare Pautasso, Faculty of Informatics, USI Lugano, Switzerland
• Erik Wilde, School of Information, UC Berkeley, USA
• Rosa Alarcon, Computer Science Department, Pontificia Universidad de Chile, Chile

Program Committee

• Jan Algermissen, Nord Software Consulting, Germany
• Subbu Allamaraju, Yahoo Inc., USA
• Mike Amudsen, USA
• Benjamin Carlyle, Australia
• Stuart Charlton, Canada
• Duncan Cragg, UK
• Joe Gregorio, Google, USA
• Michael Hausenblas, DERI, Ireland
• Ralph Johnson, University of Illinois, USA
• Rohit Khare, 4K Associates, USA
• Yves Lafon, W3C, USA
• Frank Leymann, University of Stuttgart, Germany
• Ian Robinson, Thoughtworks, UK
• Stefan Tilkov, innoQ, Germany
• Steve Vinoski, Verivue, USA
• Jim Webber, NEO4J
• Olaf Zimmermann, IBM Zurich Research Lab, Switzerland

Contact

WS-REST Web site: http://ws-rest.org/2011/
WS-REST Twitter: http://twitter.com/wsrest2011
WS-REST Email: chairs@ws-rest.org

My thanks to Microsoft for their invite and hospitality, and to the audience members for their attention and questions.

If you want to learn more about domain application protocols, hypermedia, event-driven systems with Atom, and security on the wild web – and you’re in London next week – why not sign up for a day-long REST tutorial being run by me and Jim Webber? We’re at Software Architect 2010 on Friday, 22nd October: you can register for the conference and tutorial here.

Early bird discounts apply throughout the remainder of this week.

The tutorial agenda closely follows the structure of REST in Practice, which hits the shelves later this week:

• Introduction and Motivation
• The Web Architecture
• Simple Web Integration including POX and URI tunnelling
• CRUD Services using URI templates and HTTP
• Semantics using Microformats and RDF
• Hypermedia and the REST architectural style
• Scalability and how a text-based client-server polling protocol outperforms everything else!
• ATOM and ATOMPub for event-driven and pub/sub applications
• Security
• Conclusions and further thoughts

• 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).

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.

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.

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.

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 pm – 10 pm

Location

ThoughtWorks UK Office

Berkshire House 168-173 High Holborn London WC1V 7AA