In the context of component-based systems, coordination can be thought of as an event-based <em>service</em> provided by a coordination medium.
However, this interpretation is not endorsed by some researches in the field of coordination and in particular by existing attempts to define a notion of <em>expressiveness</em> for coordination models. 

So, in this paper we elaborate on providing a new characterisation of expressiveness for coordination models, which takes into account the ability of a coordination medium to support (possibly complex) event-based coordination mechanisms, capturing and generalising features of both data-driven and control-driven coordination models.
Based on this characterisation, a formalism for denoting coordination media is developed and is proved to be fully expressive.
Examples are provided that show its ability to represent some of the main features and mechanisms of well-known models, such as Linda primitives, event notification, and expiring data.