Internet of Things – Architecture © - 66 -
technical services that e.g. a lawyer or a consultant provides). As such,
Services provide the link between the IoT aspects of a system and other, non-
IoT specific parts of an information system, like e.g. various enterprise systems;
IoT-related Services and non-IoT Services can be orchestrated together in
order to form a complete system.
As it has been pointed out in [Martín 2012], IoT-related Services need to be
explained in more detail: IoT Services provide well-defined and standardised
interfaces, hiding the complexity of accessing a variety of heterogeneous
Resources. The interaction with a Physical Entity can be accomplished via one
or more Services associated with the corresponding Virtual Entity. This
association becomes important in the process of look-up and discovery. An IoT
Service can thus be defined as a type of Service enabling interactions with the
real world.
According to [Martín 2012], IoT Services can be classified according by
their level of abstraction:
Resource-level Services expose the functionality, usually of a Device,
by accessing its hosted Resources. These kinds of Services refer to a
single Resource. In addition to exposing the Resource‘s functionality,
they deal with quality aspects, such as dependability, security (e.g.,
access control), resilience (e.g., availability) and performance (e.g.,
scalability, timeliness). Resources can also be Network Resources, i.e.
the Resources do not necessarily reside on a Device in the sense of the
IoT Domain Model (normal computers are not regarded as IoT Devices
by the IoT Domain Model), but can also be hosted somewhere else. The
concrete location of where the Network Resource is situated is
commonly abstracted away by the Service; Virtual Entity-level Services provide access to information at a Virtual
Entity-level. They can be Services associated to a single Virtual Entity
that give access to attributes for reading attribute information or for
updating attributes in order to trigger associations. An alternative is to
provide a common Virtual Entity-level Service with an interface for
accessing attributes of different Virtual Entities, as, for instance, the
NGSI Context Interface [NGSI 2010] provides for getting attribute
information of the Virtual Entities; Integrated Services are the result of a Service composition of
Resource-level or Virtual Entity-level Services as well as any
combinations of both Service abstractions.