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middleware layer and based on current efforts of standardization, with the main pur-
pose of integrating Wireless Sensor Networks (WSNs) [ 1 ] to the Web. SmartSensor
is a project developed under the sponsorship of the Brazilian National Network for
Education and Research (RNP - Rede Nacional de Ensino e Pesquisa 1 ).
In the SmartSensor project, unlike other existing initiatives [ 8 , 9 , 11 , 14 , 22 ]
that deal with the addressability and availability of all types of smart objects, the
main focus is in integrating Wireless Sensor Networks in the Web. Furthermore,
SmartSensor considers the emerging scenario where multiple WSNs from different
technologies and owners are integrated in a unique, virtual sensing infrastructure,
enabling data from different networks to be provided to various applications running
on top of them. In such scenario, theWSN itself is seen as a service (WSN as a Service
[ 3 ]), and it is possible to take full advantage of the physical infrastructure of sensor
nodes already deployed, sharing the communication and sensing resources, thus
potentially increasing the return of investment (ROI) for the infrastructure owners
and generating added value for the end users [ 16 , 35 ].
The adoption of the SmartSensor infrastructure allows WSNs to be integrated to
the Web in a transparent, seamless and flexible way. By integrating WSNs to the
Web via SmartSensor, sensor-generated data can be provided to client applications
or users exactly in the same way as documents or other Web resources. Following the
Web architecture, a resource should have a uniform resource identifier (URI) [ 28 ] and
by using URIs it is possible to navigate to/from resources and also to link resources.
It is possible to have different representations for the same resource, which is a very
powerful concept, i.e. a server can provide HTML content for human consump-
tion and eXtensible Markup Language (XML) [ 36 ] or Java Script Object Notation
(JSON) for machines. In WSNs, a resource can represent either an individual sensor
reading, the aggregate information from a set of sensors, from the whole WSN or
even from different networks connected to the infrastructure. Moreover, sensor data
can be composed with information originated from other devices and/or applications
that are available in the Web, in order to deliver value-added information to the end
user. Basically, resources are consumed in the Web by two types of clients: (i) end
users, that interact through a Web page displayed by a browser, or (ii) client appli-
cations. Such applications can be SOAP or REST-based Web services, or mashup
applications, in either case implementing an application-to-application interaction.
SmartSensor was designed from scratch to be complaint with the WoT paradigm,
thus it was built on REST (Representational State Transfer) [ 6 ] principles and relies
on current Web standards and protocols, such as HTTP (Hypertext Transfer Proto-
col) [ 25 , 26 ] and URIs (Uniform Resource Identifier). In WoT, the HTTP protocol is
not only used as a communication protocol to carry data formatted according to any
specification (as in the case of Web services technologies). Instead, HTTP is used as
the standard mechanism to support all interactions with smart objects. This interac-
tion occurs through the HTTP main operations (GET, POST, PUT and DELETE i.e.
the verbs of REST), that provide a well-defined interface to expose the functionality
of the objects in the Web. Such interface complies with the REST principles [ 6 , 8 ],
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