A ROA for the WOT

A Resource Oriented Architecture
for the Web of Things
Dominique Guinard (ETH / SAP Research / MIT Auto-ID Labs)
Vlad Trifa (ETH Zurich / SAP Research)
Erik Wilde (UC Berkeley)

INTRODUCTION AND MOTIVATION
What’s the Web of Things? What is it good for?
Dec. 1, 2010 2Dominique Guinard ETH / SAP / MIT
[http://www.flickr.com/photos/moragcasey/]

The Embedded Systems Era
 Ubiquitous:
 Home appliances
 Industries
 Smart Cities
 Connected:
 Zigbee, Bluetooth, Wifi

Finding an Application Integration Platform
 Question:
 How do we enable tech savvys and
companies to create applications on
top of this eco-system?
 Hundreds of different platforms
 Web?
 Scalable (7000 Facebook p/sec.)
 Ubiquitous (from mobile to desktop)
 Well-understood (1.73 Bio. users)
 Thesis:
 Re-use and develop Web-standards to
build a Things Universal API.

WEB OF THINGS ARCHITECTURE
Building a Web of Things, piece by piece…
[http://www.flickr.com/photos/julianbleecker]

REST: The Core of the Web
 REST: architecture with 5 constraints
1. Identify resources and links:
 A resource: something, that can and that’s worth, getting a URI and
links
2. Design respresentations
3. Use the uniform interface
4. Bring things to the Internet&Web
[2] Architectural
styles…
[1] RESTful Web
Services.

Case Study with Sun Spots
1) Resources and Links
Thanks to their atomicity services on embedded devices are
quite adapted to Resource-Oriented Architectures.
 Resources:
 Spots: http://webofthings.com/spots
 Spot 2: http://webofthings.com/spots/2
 Light Sensor: http://webofthings.com/spots/2/sensors/light
 Led Actuator:
http://webofthings.com/spots/2/actuators/led
Resource Identification Hypermedia

2) Representation Design
HTML as default, ideal for browsing:
 http://webofthings.com/spots
JSON & JSONp, ideal for mashups
XML, ideal for integration with business systems
Self-Describing Messages Hypermedia

3) Interface Design
 Leverage content negotiation:
 Accept: application/json
 Use the HTTP Verbs extensively:
 GET, PUT, POST, DELETE
 GET http://webofthings.com/spots/2/sensors/temperature
 PUT http://webofthings.com/spots/2/actuators/led/1
 Map status codes:
 200 OK, 201 Created, 400 Bad Request
Uniform Interface Self-Describing Messages

4) Bringing Things to the Internet&Web:
Smart Gateways
 6lowpan coming quickly:
 Cisco, IPSO, OpenPicus
 HTTP Reverse Proxy
 Hiding IoT proprietary protocols
(Zigbee, Bluetooth, etc.):
 Dongle based
 OSGi modularity
 Installed on residential gateways:
 Wireless routers (OpenWrt)
 NAT
 RESTful Design Process can be
(partially) automated
[3] Facilitating Integration of
Services for WoT

APPLICATIONS
What can we build on top of the Web of Things?
[http://www.flickr.com/photos/docman]

Typical WoT Architecture: « Energie Visible »
 Project for a private foundation
for sustainability (cudrefin02.ch)
 Goal: an easily deployable
system for better understanding
consumption:
 Cross-platform
 Web access
 Uses the Plogg sensor nodes
 Smart Gateway provides
RESTful API

« Energie Visible »: Mashup and UIs
 Web UI / Mashup using Javascript (GWT):
 www.webofthings.com/energievisible
 E-Meter iPhone App
[http://www.vs.inf.ethz.ch/res/show.html?what=emeter_demo]
[4] Increasing Energy
Awareness Through
Web-enabled Power
Outlets.

Physical Mashup Editors
• Clickscript:
– Javascript (JQuery / DOJO) based
visual language.
• Added wrappers for WoT
devices:
– SunSPOT, Ploggs, RFID reader
[http://www.clickscript.ch]
[5] Mashing up Your
Web-Enabled Home

EVALUATION
Ok, it’s easier to build apps upon, but is the WoT really feasible?
[ http://www.flickr.com/photos/myfwc]

Quantitative Evaluation
 10’000 requests on the Sun
SPOTs
 1) Embedded Webserver:
 205 ms (97 – 8500)
 2) Smart Gateway:
 Sync-based (caching)
 4 ms (2 – 49)
 Age max: 300 ms
 Good enough for most sub-
second use cases.

BEYOND REST
What is the Web of Things good for?
[http://www.flickr.com/photos/brapke/]

Beyond Client-Server: Real-Time Web
 Client-server paradigm not really
natural for sensing application.
 Need for sensor push.
 First step:
 Atom (cleaner RSS) / AtomPub
 Real push
 Pubsubhubbub
 HTML 5 Web
Sockets
 Server-sent
events
 RESTful XMPP

Beyond HTML: Discovering Services
 Service Discovery:
 Microformats
 HTML5 Microdata
 RDFa
 Google Custom Engine
 Yahoo Search Monkey
 Dyser

Thanks a lot for your attention
 Contact us if you want to use our
APIs in your projects:
 Dominique Guinard
 www.guinard.org
 www.webofthings.com
 Special thanks to: Simon Mayer,
Lukas Naef and Thomas Pham.

References
1. L. Richardson and S. Ruby. RESTful Web Services.
O'Reilly Media, Inc., 2007
2. R. Fielding: “Architectural styles and the design of
network-based software architectures”, 2000
3. S. Mayer, D. Guinard, V. Trifa: “Facilitating Integration and
Interaction of Real-World Services for WoT” Urban IoT
2010
4. M. Weiss, D. Guinard: “Increasing Energy Awareness
Through Web-enabled Power Outlets” MUM 2010
5. D. Guinard: “Mashing up Your Web-Enabled Home”,
Touch the Web 2010

Backup

Qualitative Evaluation
 Plogg RESTful API & Sun SPOT API used by 6
independent research labs.
 Early feedback:
 Easy to understand and use
 Straightforward testing & Web-integration
 Currently evaluating with 80 students.

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