offered over clouds of internet-connected objects, the so-called sensing as a service,
providing a “cloud-of-things”.
OpenIoT adheres to the W3C Semantic Sensor Networks (SSN) for describing
sensors and also relies on the IETFConstrainedApplication Protocol (CoAP) [ 20 ]for
the interaction with nodes and devices. The SSN ontology (Sensor and Sensor Net-
work ontology) enables the specification of formal descriptions of sensor networks,
thus allowing the semantic interoperability among networks.
As OpenIoT follows the REST principles, resources are addressed by URIs and
can have different representation formats. HTTP operations are used to interact with
the resources, through RESTful Web services.
Despite the rising popularity of IoT and the emergence of several proposals of mid-
dleware for IoT, the state-of-the-art of such proposals shows that they are still under
development. They share the ideia of seamlessly integrating a broad range of hetero-
geneous devices and offering a high level mechanism to enable developers to build
IoT applications without having to deal with heterogeneity issues.
A brief comparison of the abovementioned proposals shows that: (i) most propos-
als rely on ontologies to address the semantic interoperability between the sensed
data; (ii) the use of well-established Web services technologies is adopted by some
IoT middleware such as Hydra and OpenIoT. Both works highlight the importance
of following popular and emerging standards for IoT.
In summary, several issues remain opened, as discussed in [ 2 ], such as a fully
support for context detection and processing and for managing high volumes of
sensed data. According to Bandyopadhyay et al. [ 2 ], the current challenge is to
provide a generic IoT middleware, applicable across multiple domains.
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2. Bandyopadhyay, S., Sengupta, M., Maiti, S., & Dutta, S. (August 2011). Role of middleware
for internet of things: A study. International Journal of Computer Science and Engineering
Survey (IJCSES), 2 (3), 94-105
3. Barragn, H. Wiring project http://wiring.org.co/
4. CreativeCommons. Creative commons license attribution-sharealike 2.5 generic version. http://
5. Delicato, F. C., Pires, P. F., Pirmez, L., & Batista, T. (2010). Wireless sensor networks as a
service. In 17th IEEE International Conference and Workshops , (pp. 410-417).
6. Duquennoy, S., Grimaud, G., & Vandewalle, J. (2009). The web of things: Interconnecting
devices with high usability and performance. In International Conferences on Embedded
Software and Systems . Retrieved April 2013, from http://ieeexplore.ieee.org/stamp/stamp.jsp?