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(smart devices) and their resources, and to realize the communication with physical
objects using their provided APIs. In other words, the Smart Gateway acts as a bridge
between the Web and smart devices, by providing a RESTful Web interface to access
resources and sub resources provided by these devices and communicate with them
through their specific APIs. The gateway node plays the role of an interface between
client applications andWSNs connected to theWoT, serving as the entry point for the
submission of application requests and as a concentrator for data sent by the sensor
nodes.
In the SmartSensor architecture, a gateway node is a synonymous of a sink node,
and its functionalities are partially implemented in a computer (a PC running Debian
GNU/Linux i386 in the project) and partly on wireless communication modules
that are dependent on the different radio technologies used in WSNs. All the WSN
platforms used in the SmartSensor project adopt variations of the ZigBee protocol
[ 3 ]; therefore the sink/gateway wireless module implements this protocol to enable
the communication with sensors.
Each Smart Gateway has an IP address, runs an HTTP server and includes several
drivers, each one responsible for translating to/from proprietary protocols of the
different WSN technologies connected to the infrastructure. Thus, all Web requests
sent to a sensor node through the provided RESTful API are mapped by the gateway
to a request in the proprietary WSN API and transmitted to the respective node by
using the communication protocol understood by the device (for example, the Zigbee
protocol).
The classes and components described for the SIM logical architecture were
implemented in the Java programing language. For the Gateway Web Server, the
Apache Tomcat version 6.0.33 was used and Apache Derby relational database was
adopted as the Gateway Database. The Data Manager component is responsible
for data storage and management in the Gateway Database and its mains class is the
DataDB class . DataDB is a typical persistency class, mediating all the read and write
operations performed in the two main tables kept in the gateway. The Data_Read
table is responsible for the storage of the sensor generated data, while the Services
table contains the list of capabilities offered by each node in a given WSN.
4.2.3.2 MICA/TinyOS Sensor Plataforms
MICA motes are the category of sensor nodes manufactured by MEMSIC (formerly
Crossbow). MEMSIC technology for WSN platforms is based on the TinyOS oper-
ating system and programs to be deployed in the nodes are written in nesC language.
As specified in the MIS logical architecture, a sensor node must have three basic
functional blocks to be integrated into the SmartSensor infrastructure: Communica-
tion, Publication, and Sensor. TinyOS adopts a component-based and event-driven
programing model, and nesC is a language derived from C, so it does not natively
incorporate concepts of object-oriented programing. The main units of program-
ming in TinyOS environment are components and interfaces. Therefore, in order to
implement the functionalities of the three logical blocks defined for the sensors three
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