Internet of Things – Architecture © - 67 -
3.3.3.4 Identification of Physical Entities
In order to track and monitor Physical Entities, they have to be identified. There
are basically two ways for how this can be done, as is very well described in
[Furness 2009]: Using either natural-feature identification (classified as
―primary identification‖) or using some type of Tags or labels (classified as
―secondary identification‖) that are attached to the Physical Entity.
Both means of identification are covered in the IoT Domain Model. Tags are
modelled as Devices that explicitly identify a Physical Entity. Natural-feature
identification can be modelled, for example, by using a camera –a kind of
Sensor – that monitors the Physical Entity and an additional Resource that does
the natural feature extraction (i.e a dedicated software component). The result
of the natural-feature extraction can be used as search term for looking up the
corresponding Virtual Entity.
RFID Tags are a prominent example in IoT. As they come with their own
electronic circuitry it seems quite natural to classify RFID Tags as Devices in
terms of the IoT Domain Model. The case is less clear-cut regarding the
classification of a barcode label, however. As pointed out elsewhere [Haller
2010], classifying a barcode label as a Device seems a little far-fetched;
regarding it as a ―natural feature‖ of the Physical Entity it is attached to seems
to be more appropriate. However, as with many modelling questions, this is a
matter of taste – the IoT Domain Model is not prescribing which variant to use.
3.3.3.5 Context and location
As the IoT pertains to the physical world, the characteristics of the physical
world play an important role. All elements of the physical world are situated
within a certain context, and location is an essential aspect of this context. All
concepts in the IoT Domain Model that refer to elements of the physical world,
i.e., Physical Entities, Devices, and Human Users inherently have a location.
This location may or may not be known within the IoT system.
The location of a Physical Entity can be modelled as an attribute of a Virtual
Entity. This location can then be provided through Resources. In the case of a
stationary Physical Entity, the Resource providing the location can be an On-
Device (storage) Resource, in the case of a mobile Physical Entity the
Resource could be a positioning system like GPS, or a tracking system like
existing indoor location systems.