team and it is based on the Resource Description Framework (RDF) [ 23 ] data model.
The behavior engine parses an SPL document and loads it in the beliefs storage.
Each agent has a behavior model. Interoperability between heterogeneous resources
is achieved by semantic adaptation and by assigning a proactive agent to each of the
Thus, this middleware is a multi-agent system where interoperability among the
resources is supported by using agents, metadata and ontologies.
The Hydra middleware [ 11 ] consists of a service-oriented architecture that relies
on Web services to support the resource discovery, description and access based on
XML and web protocols. It distinguishes resource restricted devices that are not able
to host the middleware, and more powerful devices (Hydra-enabled devices). Each
Hydra-enabled device hosts a Network Manager component, that is responsible for
communication among devices. A proxy is used to connect the restricted devices
to the Hydra network. Proxies are deployed on Hydra-enabled devices that act as
gateways. Such proxies provide Web service interfaces for accessing a device.
The two main tasks performed by Hydra developers are: (i) integrating non-Hydra
devices; and (ii) connecting Hydra-enabled devices to a network.
2.2.3 LinkSmart Middleware
The LinkSmart middleware [ 7 ], developed in the Hydra project, enables the integra-
tion of heterogeneous physical devices into applications via a Web service interface
for controlling any type of physical device irrespective of its network technology
such as Bluetooth, RF, ZigBee, RFID, WiFi, etc. The middleware name is different
from the project name because it has been registered in Germany and used by the
Hydra middleware, discussed in the previous subsection.
LinkSmart is based on a semantic model-driven architecture and enables the use
of devices as services both by embedding services in devices and by proxy services
for devices. The semantic description of devices is based on ontologies using OWL,
OWL-s and SAWSDL.
The OpenIoT project [ 21 ] provides an open-source middleware platform to enable
the development of IoT applications according to a utility cloud computing delivery
model. OPENIoT goal is to realize the idea of on demand access to IoT services