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to the web-of-things (P
sterer 2011 ). The use of web-based technologies in IoT
applications is expected to facilitate the engagement of large masses of web and mobile
applications developers in the creation of innovative IoT based ideas and services. The
approach introduced in coming section is in-line with this direction.
3 OpenIoT Middleware Platform
Foundations for an IoT
Services Visual Development Paradigm
-
Our approach to visually designing, implementing and deploying IoT application
hinges on the OpenIoT middleware platform, which is available as open source soft-
ware. The OpenIoT platform, as shown in Fig. 1 , provides the means for representing
sensor data and metadata according to the W3C SSN ontology, but also for persisting
the data within cloud infrastructures. Furthermore, the OpenIoT platform de
nes the
notion of IoT services as SPARQL queries, which enables the dynamic discovery of
sensor data and metadata, along with the execution of queries over arbitrary large
numbers of geographically and administratively distributed sensors. At the same time,
OpenIoT provides the means for collecting data streams from physical and virtual
sensors and accordingly for transforming them to W3 SSN compliant data streams.
Overall, the main elements of the OpenIoT platform are:
The Sensor Middleware, which collects,
lters and combines data streams stem-
ming from virtual sensors (e.g., signal processing algorithms, information fusion
algorithms and social media data streams) or physical sensing devices (such as
temperature sensors, humidity sensors and weather stations). This middleware
acts as a hub between the OpenIoT platform and the physical world, since it enables
access to information stemming from the real world. Furthermore, it facilitates the
interfacing to a variety of physical and virtual sensors such as IETF CoAP com-
pliant sensors (i.e. sensors providing RESTful interfaces), data streams from other
IoT platforms (such as https://xively.com ) and social networks (such as Twitter).
Among the main characteristics of the sensor middleware is its ability to stream W3
SSN compliant sensor data in the cloud. The Sensor Middleware is deployed on the
basis of one or more distributed instances (nodes), which may belong to different
administrative entities. The prototype implementation of the OpenIoT platform uses
an enhanced/extended version of the GSN middleware (Aberer 2007 ) (namely
X-GSN, which is currently as a module of the OpenIoT open source project).
However, other sensor middleware platforms could be also used in alternative
implementations and deployments of the OpenIoT architecture.
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The Cloud Computing Infrastructure, which stores data streams stemming from
the sensor middleware thereby acting as a cloud database. The cloud infrastructure
stores also metadata for the various IoT services, which are made available to
the visual development tools of the following section. Note that the cloud infra-
structure could be either a public infrastructure (such as the Amazon Elastic
Compute Cloud (EC2)) or a private infrastructure (e.g., a private cloud deployed
based on Open Stack ( http://www.openstack.org/ ) ). The cloud infrastructure can be
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