Design Decisions

The common language inherits from IF some of its main features, in particular:

• structuring concepts: systems consist of processes, running in parallel and communicating through message passing via communication buffers;
• communication primitives: more exactly, processes may communicate either through signal exchange (directly or via signalroutes) or through shared variables;
• real-time primitives: each process may use several clocks to measure time during the execution and, in addition, transitions may be guarded with time constraints (depending on clocks) and decorated with explicit (eager, delayable, lazy) deadlines;
• open systems: the language offers the concept of open communication channel, connected to the environment, and transporting messages between it and the system;
• non-determinism: processes may be non-deterministic i.e, more than one transition may be enabled at some control state, and all situations have to be considered at execution;
• complex data types: the language provide several type constructors such as enumeration, range, array, record, abstract as well as predefined basic types in order to simplify complex data description and manipulation;

In order to fit the new requirements, the common language improves the IF language in several directions, the most important being listed below:

• parameterization: using integer constants it is now possible to parameterize data types (i.e, size of arrays), system configurations (i.e, number of instances), timing behavior (i.e, clock constraints)...;
• dynamic features: the language include dynamic creation and destruction of process and signalroute (channel) instances. This makes system configuration to be dynamic, that is, the number of components running (and in turn, the number of clocks ...) may change during execution;
• structured control: the common language integrates hierarchical states (to structure automata) and,
• composed transitions: basic control statements such as if-then-else and while-do are provided to structure automata transitions;
• external code integration: the common language provide a simple an elegant way to abstract complex transformations on data through the integration of external code within procedures. The external code to be provided depend on tools used i.e, an executable implementation in order to simulate and model check, or a first-order axiomatic definition in order to use it inside a prover, etc.