Workflow Variability for Autonomic IoT Systems

Abstract

Autonomic IoT systems require variable behaviour at runtime to adapt to different system contexts. Building suitable models that span both design-time and runtime is thus essential for such systems. However, existing approaches separate the variability model from the behavioural model, leading to synchronization issues such as the need for dynamic reconfiguration and dependency management. Some approaches define a fixed number of behaviour variants and are therefore unsuitable for highly variable contexts. This paper extends the semantics of the DX-MAN service model so as to combine variability with behaviour. The model allows the design of composite services that define an infinite number of workflow variants which can be chosen at runtime without any reconfiguration mechanism. We describe the autonomic capabilities of our model by using a case study in the domain of smart homes.

Evaluating IoT service composition mechanisms for the scalability of IoT systems

“…DX-MAN [157,158,159] is a model that uses exogenous composition operators [160,161] to algebraically compose IoT services in a hierarchical bottom-up manner. The result of composition is not a workflow, but an IoT composite service which is semantically equivalent to a potentially infinite family of (explicit) workflow control flows.…”

“…Workflow variability [157,208] allows the definition of alternative control flow constructs (i.e., behaviours) in a service composition (see Figure 12), and it is particularly useful for autonomously changing workflows at runtime. For instance, the SensorNetwork composite may define variable parallel behaviours for pulling data, depending on a vehicle's location.…”

“…In order to define workflow variability, a service composition mechanism must enable total compositionality by which all behaviours (e.g., operations) from the composed services are semantically available in a composite service [157,159]. This concept contrasts with partial compositionality where only named and selected behaviours are semantically preserved, leading to a combinatorial explosion of behaviours as the number of services increases [159].…”

“…DX-MAN [157,158,159] is an algebraic model where IoT services and service composition operators are first-class semantic entities. A service is a stateless distributed unit of composition which can be either atomic or composite, and its semantics is a workflow space (i.e., a family of workflow variants).…”

“…is the total number of atomic sub-service operations plus the number of composite sub-workflow spaces. For further details on this matter, see [157]. In addition to composition operators, DX-MAN provides special transformation operators (called adapters) for sequencing, branching, parallelising, looping and guarding over individual workflow spaces.…”