  Communications system design has been traditionally guided by task-agnostic
principles, which aim at efficiently transmitting as many correct bits as
possible through a given channel. However, in the era of cyber-physical
systems, the effectiveness of communications is not dictated simply by the bit
rate, but most importantly by the efficient completion of the task in hand,
e.g., controlling remotely a robot, automating a production line or
collaboratively sensing through a drone swarm. In parallel, it is projected
that by 2023, half of the worldwide network connections will be among machines
rather than humans. In this context, it is crucial to establish a new paradigm
for designing communications strategies for multi-agent cyber-physical systems.
This is a daunting task, since it requires a combination of principles from
information, communication, control theories and computer science in order to
formalize a general framework for task-oriented communication design. In this
direction, this paper reviews and structures the relevant theoretical work
across a wide range of scientific communities. Subsequently, it proposes a
general conceptual framework for task-oriented communication design, along with
its specializations according to the targeted use case. Furthermore, it
provides a survey of relevant contributions in dominant applications, such as
industrial internet of things, multi-UAV systems, tactile internet, autonomous
vehicles, distributed learning systems, smart manufacturing plants and 5G and
beyond self-organizing networks. Finally, it highlights the most important open
research topics from both the theoretical framework and application points of
view.
