Internet of Things – Architecture © - 77 -
3.5.2.2 Service Organisation
The Service Organisation FG is a central Functionality Group that acts as a
communication hub between several other Functionality Groups. Since the
primary concept of communication within the IoT ARM is the notion of the
Service (see Domain Model in Section 3.3), the Service Organisation FG is
used for composing and orchestrating Services of different levels of abstraction.
Within the IoT Reference Architecture, it effectively links the Service requests
from high level FGs such as the IoT Process Management FG, or even external
applications, to basic services that expose Resources (see Domain Model
Section 3.3) (such as services hosted on a WSN gateway), and enables the
association of entities with these services by utilising the Virtual Entity FG, so
that a translation of high-level requests dealing with properties of entities (e.g.,
―give me please the temperature in the room 123‖) down to the concrete IoT
services (e.g., ―sensor service XYZ‖) can be realised. In order to allow for
querying Virtual Entities or IoT Services that are associated with these entities,
the Service Organisation FG is responsible for resolving and orchestrating IoT
Services and also deal with the composition and choreography of Services.
Service Composition is a central concept within the architecture, since IoT
Services are very frequently capable of rather limited functionality due to the
constraints in computing power and battery life that are typical for WS&ANs or
embedded Devices comprising the IoT. Service Composition then helps
combining multiple of such basic Services in order to answer requests at a
higher level of Service abstraction (e.g. the combination of a humidity sensing
Service and a temperature Service could serve as input for an air-conditioning).
Service Choreography is a concept that supports brokerage of Services so that
Services can subscribe to other Services available in the system.
As discussed in the previous section, the Service Organisation FG is closely
tied to the IoT Process Management FG, since the Service Organisation FG
enables (business) processes or external applications to find and bind Services
that can be used to execute process steps, or to be integrated in other ways
with external applications. The Service Organisation FG acts as an essential
enabler for the IoT Process Management FG. The Virtual Entities specified
during the process-modelling phase are resolved and bound to IoT Service FG
needed for process execution.
3.5.2.3 Virtual Entity and IoT Service
The Virtual Entity and IoT Service FGs include functions that relate to
interactions on the Virtual Entity and IoT Service abstraction levels,
respectively. Figure 15 shows the abstraction levels and how they are related.
On the left side of Figure 15 , the physical world is depicted. In the physical
world, there are a number of Sensors and Actuators that capture and facilitate
the change of certain aspects of the physical world. The Resources associated
to the Sensors and Actuators are exposed as IoT Services on the IoT Service