1. Resource Oriented
Architecture in
Wireless Sensor Network
Sun SPOT Smart Logger in the
context of a supply chain
SYSTEMATIC THOUGHT LEADERSHIP FOR INNOVATIVE BUSINESS
Thomas Pham, Intern at SAP Research CEC Zürich (Switzerland)
January 2009

2. Outline of the
presentation
1. Introduction
1.1. Context of the project
1.2. Approach : DPWS vs REST
2. Integration Scenario : Video presentation
3. The system Components
3.1. Global Overview
3.2. The Enterprise Logistics Application
3.3. The Gateway Application
3.4. The Sun SPOT Application
4. The encountered difficulties
5. Future Work
6. Conclusion
© SAP 2007 / Page 2

3. Introduction
Internship : SAP Research CEC Zürich
Diploma Work : University of Applied Sciences of
Western Switzerland
How to integrate and simplify the interoperability of
heterogeneous and limited devices in sensors
networks with existing information systems ?
© SAP 2007 / Page 5

4. 1.1 Context of the project
SOCRADES :
(Service-Oriented Cross-layer InfRAstructure for Distributed smart Embedded deviceS)
 European R&D project, 15 partners from 6 countries
 SAP’s contribution is in the enterprise integration
 Need to increased flexibility and agility of
manufacturing processes
 The challenge : coupling high-level back-end
systems (e.g. ERP) with shop-floor Smart Devices
Web Services based shop floor integration

Enable dynamic reconfiguration of devices

High level services compositions

Automatic workflow processing

...

> Need to integrate all kind of heterogeneous and
distributed devices with existing information systems
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5. 1.2 Approach : DPWS vs REST
SOCRADES : is based on Service Oriented Architecture
 Use DPWS (Device Profile for Web Services)
Based on WS-* standards for providing (Big) Web

Services at the device level
 But, ... for limited devices it involves :
Complex XML messages (e.g. WSDL, SOAP)

Redundancy and addition of useless XML contents

Less space storage, limited bandwidth

More “calculation power”, less battery’s autonomy

Strong-coupling : fixed integration scenario

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6. 1.2 Approach : DPWS vs REST
Our Approach : a Resource Oriented Architecture
 REST (Representational State Transfer) Web Services
 Based on existing Web standards :
HTTP + URI + Hypermedias
 Resource & Representation concepts
 Light , simple
 uniform interfaces (GET, POST, ...)
 Flexible and easily integrable
 JSON (JavaScript Object Notation) as interchange format
 more compact than XML
 easier for human comprehension
Objectives :
 Prototype : REST concepts on limited devices
 Design an integration scenario
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7. Integration Scenario
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8. Video presentation
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9. The System Components
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10. 3.1 Global Overview
Example of network topology in which the system
could be integrated :
A. The Enterprise Logistics Application

– manage users and theirs deliveries
track shipments and events notifications
–
B.

1. The gateway Application

– devices discovery & forward communications
 2. The device’s Manager
browse and manage software & hardware
–
resources
 C. The embedded Application on sensors device
tiny HTTP Web server
–
– periodic values sampling
– rules monitoring system
– provide event notifications
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11. 3.2 The Enterprise Logistics Application
Developed JAVA with J2EE Standards

 EJB 3
 JPA + TopLink
 WS-*
 JSP + JSF
SAP : JAVA is the main computer language for new

technologies.
SAP Solutions compliant with J2EE standards

Glassfish Application Server :

 instead of SAP Netweaver CE, because
 better suited to a quick prototyping
REST / WS Adapter is the notification endpoint

 enable devices to send their message “RESTfuly”
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12. 3.3 The Gateway Application
 The “server” : act as bi-directional proxy bridge between networks
 use of RESTlet framework : provide a standalone Web server
 simplify and rebuild HTTP messages
 register and manage Sun SPOT connections of new discovered devices
 The “client” : HTML + AJAX application developed with GWT
 async XmlHttpRequest to the resources
 access to device’s resources via : http://{gateway_ip:port}/{spot_name}/ ...
802.15.4
TCP / IP
Wireless
Connection
Connection
Gateway Application Server
Outgoing
WebServers
Request/Response
Forwarder
Périphérique
de capteurs
UI
Enterprise
Client
Enterprise Server
Application
WebServer
UI
Enterprise
GatewayID Client
UI Gateway
Broadcaster Application
Client
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13. 3.4 The Sun SPOT Application
Developed in J2ME on Squawk JVM
 Gateway locator,
 tinyWeb Server
 De/serialize HTTP resquest/response
 provide resources tree
(actuators/sensors/management)
 HTTP methods : GET, POST, UPDATE, DELETE
 CRUD signification
 Resources allow parameters
(application/x-www-form-urlencoded)
 provide rules system for sensors values monitoring
 HTTP client to push event notifications to the endpoint
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14. 4. The encountered difficulties
Principally with Sun SPOT : few documentation, experimental technology
 no TCP/IP implementation stack on Sun SPOT 802.15.4 network :
 involves no possibility to directly address devices
 soon IPv6-over-LowPan
 Particularities of Sun SPOT API & strange behaviors
 no device discovery protocol
 negotiation to open StreamConnection (MAC + port)
 Sun SPOT debugging
 not possible via USB
 only remotely by the air via the Sun SPOT BaseStation
 but ... as it was dedicated to the Gateway Application -> problem
 solution : use of another Sun SPOT acting as it.
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15. 5. Future Work
 Request/response Buffer on the Gateway
Limit solicitations of the limited devices to ensure :

better responsiveness
–
autonomy
–
 The JSON structure that represent embedded resources
Our solution is quite personal :

because it doesn’t exist a standard JSON structure representing resources of
–
sensors
Solution to explore :

RDF/JSON (Resources Description Framework)
–
open the way of Semantic Sensor Web
–
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16. 6. Conclusion
 Existing Web standards on any embedded devices :
enable a simple interoperability of heterogeneous devices

improve the flexibility and adaptability of various device’s components

facilitate the integration with professional business applications

 For me :
rewarding experience

discover a lot of new technologies

Collaborations with dynamic and interesting smart people

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17. Thanks for your attention !
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18. Your questions ?
For more informations, please to contact :
dominique.guinard@sap.com
mihai.vlad.trifa@sap.com
thomas.pham@ithings.ch
© SAP 2007 / Page 5