Internet of Things – Architecture © - 78 -
level. Example interactions between applications and the IoT system on this
abstraction level are ―Give me the value of Sensor 456‖ or ―Set Actuator 867 to
On‖. Applications can only interact with these Services in a meaningful way, if
they already know the semantics of the values, e.g. if Sensor 456 returns the
value 20, the application has to be programmed or configured in such a way
that it knows that this is the outdoor temperature of the car of interest, e.g. Car
MXD - 123. So, on this level no semantics is encoded in the information itself,
nor does the IoT system have this information, it has to be a-priori shared
between the Sensor and the application.
Whereas interaction on the IoT Service level is useful for a certain set of
applications that are programmed or configured for a specific environment,
there is another set of applications that wants to opportunistically use suitable
Services in a possibly changing environment. For these types of applications,
and especially the Human Users of such applications, the Virtual Entity level
models higher-level aspects of the physical world, and these aspects can be
used for discovering Services. Examples for interactions between applications
and the IoT system on this abstraction level are ―Give me the outdoor
temperature of Car MXD - 123‖ or ―Set lock of Car MXD – 123 to locked‖. To
support the interactions on the Virtual Entity level, the relation between IoT
Services and Virtual Entities needs to be modelled, which is done in form of
associations. For example, the association will contain the information that the
outdoor temperature of Car MXD - 123 is provided by Sensor 456. Associations
between Virtual Entities and IoT Services are modelled in the Information Model
(Section 3.4).
Figure 15 : IoT Service and VE abstraction levels.