Internet of Things – Architecture © - 60 -
software applications, agents or Services that may access other Services
or Resources. Passive Digital Artefacts (PDA) are passive software
elements such as database entries that can be digital representations of
the Physical Entity. Please note that all Digital Artefacts can be classified
as either Active or Passive Digital Artefacts; Ideally, Virtual Entities are synchronised representations of a given set of
aspects (or properties) of the Physical Entity. This means that relevant
digital parameters representing the characteristics of the Physical Entity
are updated upon any change of the former. In the same way, changes
that affect the Virtual Entity could manifest themselves in the Physical
Entity. For instance, manually locking a door might result in changing the
state of the door in home automation software, and correspondingly,
setting the door to ―locked‖ in the software might result in triggering an
electric lock in the physical world.At this point it should be noted that while Figure 9 , at first sight, seems to
suggest only a Human User interacting with some Physical Entities, it also
covers interaction between two machines: in this case, the controlling software
of the first machine is an Active Digital Artefact and thus a User, and the second
machine – or a Device in the terms of the IoT Domain Model – can be modelled
as a Physical Entity. We introduce the concept of an Augmented Entity as the
composition of one Virtual Entity and the Physical Entity it is associated to, in
order to highlight the fact that these two concepts belong together. The
Augmented Entity is what actually enables everyday objects to become part of
digital processes, thus, the Augmented Entity can be regarded as constituting
the ―Thing‖ in the Internet of Things.
It should be noted that there might be many types of users, as we have
discussed before. A Human User is a specialisation of the general concept.
However, different kinds of Users, such as maintenance people, owners, or
security officers are plausible as well. It is also worth noting that we have not
included different roles in the IoT Domain Model, for same reason that we have
also not introduced different types of Users. Within the development of concrete
architectures, it is very likely that the Users will take on different roles and these
should be modelled accordingly. As the underlying taxonomies will vary with the
use cases addressed, we do not prescribe a specific taxonomy here. Especially
in the enterprise domain, where security roles are fundamental to practically
every single IoT architecture, one common option for modelling roles can be
found in [Raymond 1995]). We will briefly revisit up this taxonomy with in the
context of the ―Process Management‖ Section (see Section 3.5.2.1).
The relationship between Augmented, Physical and Virtual Entities is shown in
Figure 10 , together with other terms and concepts that are introduced in the
remainder of this section.