OpenIoT: Open Source Internet-of-Things in the Cloud - Interoperability and Open-Source Solutions for the Internet of Things - page 17

Fig. 2. High-level OpenIoT Publish/Subscribe Architecture

devices into the platform to be annotated and stored in the RDF repository, and sub-
sequently to be transmitted in near real-time to adequate mobile devices.
Since the load of the publish/subscribe processing engine is generated by a varying
number of publishers and subscribers with changing joint publication rate, the engine
offers elastic real-time computation. It processes many subscriptions in parallel, which
minimizes the processing overhead and optimizes the usage of cloud resources under
varying load.

3 OpenIoT Platform Capabilities

3.1 Sensors and Data Streams Registration, Deployment and Discovery

OpenIoT manages the registration, data acquisition and deployment of sensors and
interconnected objects, through X-GSN. X-GSN is an extension of the GSN that
supports semantic annotation of both sensor data and metadata. The core fundamental
concept in X-GSN is the virtual sensor, which can represent not only physical devices,
but in general any abstract or concrete entity that observes features of any kind.
A virtual sensor can also be an aggregation or computation over other virtual sensors,
or even represent a mathematical model of a sensing environment.
In order to propagate its data to the rest of the OpenIoT platform, each virtual
sensor needs to register within the LSM, so that other applications and users can
discover them and get access to their data. The sensor is registered through X-GSN by
posting a semantically annotated representation of its metadata. In order to associate
metadata with a virtual sensor, a simple metadata descriptor is used. X-GSN takes care
of creating the semantic annotations in RDF, according to the OpenIoT ontology, and
posting them to the LSM cloud store repository.