Contents Erik Wilde: REST: Growing Up

2Abstract
3Eierlegende Wollmilchsau?
4Toolbox!
1 WS-REST Turns 6!
- 6Happy 6th Anniversary!
- 7WS-REST: Looking Back
- 8Papers at WS-REST
- 9REST Style Elements
- 10Using Style Elements to Solve SOA Problems
- 11IoT Scenarios
2 Resource Discovery
- 13Where are my Resources?
- 14IoT Drives Discovery
- 15Discovery Design
3 Resource Capabilities
- 17What Can My Resource Do?
- 18What's the Link Interaction?
4 Testing REST
- 20Why Test REST?
- 21How Robust Is My Client?
- 22Resource Identification
- 23Resource Access
- 24Resource Representation
- 25Resource Variability
5 No Silver Unicorn
- 27Creating the Silver Unicorn Hammer
- 28Embrace Diversity
- 29Service Documentation
- 30Hypermedia Patterns
6 Conclusions
- 32REST: What's Next?
- 33Thanks! Q&A

Erik Wilde: REST: Growing Up

(2) Abstract

REST's popularity as a design pattern for providing services has steadily gained traction over the last decade. While this is great news because more decentralized and browsable services become available, it also creates the risk of attempting to create REST standards. After looking back at REST's success (and WS-REST's 6-year history), this talk is an attempt to present REST as a pattern and a practice, and not as a technology that needs standardized technologies and tools. As REST practitioners, our goal should be to create solutions that are a good fit for their problem space, instead of attempting to create the single one solution that we can simply use everywhere.

WS-REST Turns 6!

Outline (WS-REST Turns 6!)

WS-REST Turns 6! [6]
Resource Discovery [3]
Resource Capabilities [2]
Testing REST [6]
No Silver Unicorn [4]
Conclusions [2]

WS-REST Turns 6! Erik Wilde: REST: Growing Up

(6) Happy 6th Anniversary!

WS-REST Turns 6! Erik Wilde: REST: Growing Up

(7) WS-REST: Looking Back

Six workshops all over the globe
- WS-REST 2010 [http://ws-rest.org/2010/] hosted by WWW2010 in Raleigh, NC, USA
- WS-REST 2011 [http://ws-rest.org/2011/] hosted by WWW2011 in Hyderabad, India
- WS-REST 2012 [http://ws-rest.org/2012/] hosted by WWW2012 in Lyon, France
- WS-REST 2013 [http://ws-rest.org/2013/] hosted by WWW2013 in Rio de Janeiro, Brazil
- WS-REST 2014 [http://ws-rest.org/2014/] hosted by WWW2014 in Seoul, Korea
- WS-REST 2015 [http://ws-rest.org/2015/] hosted by WWW2015 in Firenze, Italy
Two books of revised and extended workshop papers
- REST: From Research to Practice [http://ws-rest.org/book/] published by Springer
- REST: Advanced Research Topics and Practical Applications [http://ws-rest.org/book/2/] published by Springer

WS-REST Turns 6! Erik Wilde: REST: Growing Up

(8) Papers at WS-REST

From applications to frameworks
- Initially there were mostly papers on specific RESTful designs
- This shifted to papers about general-purpose designs and frameworks
REST's status as an architectural style is a challenge
1. You can apply the style to a specific problem and present the solution
2. You can attempt to codify the style in a framework as a generic solution
3. Or you can deconstruct the style into style elements

WS-REST Turns 6! Erik Wilde: REST: Growing Up

(9) REST Style Elements

A set of constraints that establish the REST architectural style

Resource Identification
Uniform Interface
Self-Describing Messages
Hypermedia Driving Application State (HATEOAS)
Stateless Interactions

WS-REST Turns 6! Erik Wilde: REST: Growing Up

(10) Using Style Elements to Solve SOA Problems

REST is not intended to be the answer to all problems in IT services
- Trading optimization of tight coupling for evolvability of loose coupling
REST works best for large-scale scenarios with decentralized evolution
Evolution can happen on a variety of axes
- Open media types allow for extensions and non-breaking versioning
- Link types allow to establish new relationships between resources
- New media types can be introduced and deployed incrementally

WS-REST Turns 6! Erik Wilde: REST: Growing Up

(11) IoT Scenarios

IoT's next logical step is the Web of Things (WoT)
WoT is nothing more than applying REST to IoT resources
How likely is it that all IoT resources use one media type?
- Probably similar to the likelihood that all Web services use the same media type
- Why not share patterns instead of trying to share technologies?

Resource Discovery

Outline (Resource Discovery)

WS-REST Turns 6! [6]
Resource Discovery [3]
Resource Capabilities [2]
Testing REST [6]
No Silver Unicorn [4]
Conclusions [2]

Resource Discovery Erik Wilde: REST: Growing Up

(13) Where are my Resources?

REST requires identification but has no specific discovery
- Without resource identifiers, there can be no REST
- There is no specific discovery protocol in the REST style
- Without discovery, living in an open and decentralized world is impossible
- Discovery is just another service! Here's a rather popular one! [http://www.google.com/]
Discovery is covered by REST and does not need special treatment
- Formats such as Atom or Activity Streams essentially are discovery protocols

Resource Discovery Erik Wilde: REST: Growing Up

(14) IoT Drives Discovery

Gartner predicts 5 billion connected things in 2015 [http://www.gartner.com/newsroom/id/2905717]
- … and 25 billion by 2020
- Many things will be indirectly and/or intermittently connected
IoT establishes connectivity, WoT establishes actionability
Many IoT scenarios today are closed verticals
- We're re-living the pre-Web era of the Internet
- Currently, IoT seems to go the way of Social: Siloization
After discovery, WoT resources should be usable anywhere on the Web

Resource Discovery Erik Wilde: REST: Growing Up

(15) Discovery Design

IoT/WoT makes core REST principles even more important
- Write resilient clients that can deal with failing interactions
- Do not hardcode URI patterns anywhere in your client code
Cloud lock-in is one of the big anti-patterns of today
- Sometimes strategic, sometimes simply cloud-age mainframe thinking
- If your cloud is not linkable with other clouds, you have a problem
- Clouds are implementation details below the REST level
Discovery should be able to discover anything with a URI
- IoT protocols manage connectivity issues at lower levels

Resource Capabilities

Outline (Resource Capabilities)

WS-REST Turns 6! [6]
Resource Discovery [3]
Resource Capabilities [2]
Testing REST [6]
No Silver Unicorn [4]
Conclusions [2]

Resource Capabilities Erik Wilde: REST: Growing Up

(17) What Can My Resource Do?

Discovery is the first step to find new resources
- Second step is to understand the resource
IoT challenge is the extreme variability in resource capabilities
- Most likely, certain classes of IoT resources/scenarios can share sets of concepts
- Domain experts should provide the bounded contexts of those classes
REST's service description is the media type specification
- Large design spectrum between generic and specific description models
- Making service descriptions as simple as possible is the way to go

Resource Capabilities Erik Wilde: REST: Growing Up

(18) What's the Link Interaction?

How to follow a link? is a core REST question
URI scheme provides the framework for possible interactions
Link source provides additional hints
- Hints can be hardcoded or through affordances for encoding interaction instructions
- Interactions should be stateless, so link source should never be required
Solution: Embed link description but also make it standalone
- Resources can provide link descriptions as interaction instructions
- Link sources can make instructions narrower when required by context
Attempted in a variety of places, but nothing seems to stick

Testing REST

Outline (Testing REST)

WS-REST Turns 6! [6]
Resource Discovery [3]
Resource Capabilities [2]
Testing REST [6]
No Silver Unicorn [4]
Conclusions [2]