OpenIoT: Open Source Internet-of-Things in the Cloud - Interoperability and Open-Source Solutions for the Internet of Things - page 16

Stream Data are continuous. Continuous queries are rst registered in the system, and

continuously executed as new data arrives, with new results being output as soon as
they are produced. LSM provides a wide range of interfaces (wrappers) for accessing
sensor readings such as physical connections, middleware APIs, and database con-
nections. Each wrapper is pluggable at runtime so that wrappers can be developed to
connect new types of sensors into a live system when the system is running. The
wrappers output the data in a uni ed format, following the data layout described in the

OpenIoT ontology.

2.3 Mobile Broker and Publish/Subscribe Middleware

OpenIoT offers support for discovering and collecting data from mobile sensors (e.g.,
wearable sensors, sensors built-in mobile devices). This is achieved through a publish/
subscribe middleware titled CloUd-based Publish/Subscribe middleware for the IoT
(CUPUS) which integrates: (1) A cloud-based processing engine for sensor data
streams based on the publish/subscribe principles and (2) A mobile broker running on
mobile devices for flexible data acquisition from mobile ICOs. In the OpenIoT
architecture, CUPUS interfaces to the Cloud Database via X-GSN which annotates the
data collected from mobile devices. Hence, data streams from mobile ICOs are
annotated and stored in the OpenIoT cloud via X-GSN, similar to the way data streams
from stationary sensors are announced via the X-GSN sensor middleware.
CUPUS supports content-based publish/subscribe processing, i.e., stateless Bool-
ean subscriptions with an expressive set of operators for the most common data types
(relational and set operators, pre x operators on strings, and the SQL

BETWEEN operator), and continuous top-k processing over sliding windows i.e. a
novel publish/subscribe operator which identi

x and suf

es k best-ranked data objects with
respect to a given scoring function over a sliding window [ 9 ]. It facilitates pre- ltering

of sensor data streams close to data sources, so that only data objects of interest, value
and relevance to users are pushed into the cloud. The ltering process is not guided

locally on mobile devices, but rather from the cloud based on global requirements.
Moreover, CUPUS distributes in near real-time push-based noti

cations from the cloud
to largely distributed destinations, e.g., mobile devices, based on user information
needs.
As depicted in Fig. 2 , a Mobile Broker (MB) running on a mobile device can
connect to and disconnect from a publish/subscribe processing engine running within
the cloud. On the one hand, a device with attached sensors acts as a data source: The
MB announces the type of data it is able to contribute to the platform and adds the
sensor to the Cloud Data Storage. On the other hand, mobile phone users can de ne

continuous requests for data in the form of subscriptions. Based on existing requests for
sensor data expressed through subscriptions by either mobile device users or the
OpenIoT platform, the MB receives subscriptions from the publish/subscribe pro-
cessing engine which become data lters to prevent potential data overload within the
cloud. This mechanism ensures that only relevant data is transmitted from mobile