messages requesting for a given sensing task/data, and (iii) sending reply messages in
response to request messages (after the required sensing tasks have been performed).
This component includes classes responsible for keeping the current state of the sen-
sor nodes, both regarding the available resources, such as residual energy, and the
acquired sensing data. As the data collected by the sensing units are not always imme-
diately transmitted (depending on the data delivery model required by the application
and also on the adopted data aggregation intervals), the classes of this component
shall keep the data in the node memory until they are processed and sent through the
network towards the gateway.
220.127.116.11 Publish and Discovery
The classes of this component are responsible for implementing the internal discovery
service. Therefore, a class is required to createmessages advertising the node features
and send these messages whenever required. Classes of the Publish-Discovery and
the Sensor components directly depend on the low-level primitives provided by the
sensor operation system.
4.2.3 The SIM Physical Architecture
The logical architecture previously described for SIM was instantiated on a gateway
node implemented in Java and on sensor nodes from three different technologies:
Mica platform/TinyOS, Arduino and Sun Spot. In the next subsections we describe
the gateway physical architecture and the components for the MICA/TinyOS plat-
form. Description of the components implemented for Arduino and Sun Spot plat-
forms are outside the scope of the topic.
18.104.22.168 WoT Gateway
Despite the REST principles are suitable for the integration of physical devices to the
WoT, such devices do not always have sufficient computational resources to support
an embedded server. Therefore, the direct integration of real-world devices with
the Web is still a complex task, especially in cases of extremely limited resources
devices such as the sensor nodes in a WSN. In such cases, a different strategy for
the integration should be adopted, based on the utilization of an intermediate device,
Smart Gateway orWoT gateway. Smart Gateways have two basic functions: to expose
a RESTful interface via URIs that identify and provide access to physical objects