Languages and Models for Collective Adaptive Systems

			   Rocco De Nicola 

			      IMT Lucca

Collective Adaptive Systems (CAS) are systems that consist of a large
number of interacting components that dynamically adjust and combine
their behaviour to achieve specific goals. We propose a set of
programming abstractions that have been specifically designed to deal
with CAS, and with their need to adapt to the changes of the working
environment and to the evolving requirements. Based on these
abstractions, we introduce SCEL (Software Component Ensemble
Language), a kernel language whose solid semantic foundations lay also
the basis for formal reasoning on CAS. One of the key feature of SCEL
is the so called “attribute-based communication”, an alternative to
broadcast and to binary communication. Building on this, we introduce
also a basic process calculus, named AbC, whose primary primitive for
interaction is exactly attribute-based communication. An AbC system
consists of a set of parallel components each of which is equipped
with a set of attributes. Communication takes place in an implicit
multi-cast fashion, and interactions among components are dynamically
established by taking into account “connections” as determined by
predicates over the attributes exposed by components. Expressiveness
and effectiveness of AbC are demonstrated both in terms of the ability
to model scenarios featuring collaboration, reconfiguration, and
adaptation and of the possibility of encoding a process calculus for
broadcasting channel-based communication and other communication
paradigms. Behavioural equivalences for AbC are introduced for
establishing formal relationships between different descriptions of
the same system.