The expressive power of LOTOS behaviour expressions

It is a known result that, when in a process algebra like LOTOS we have both recursion and parallel composition operators, the finite-state behaviour of processes is in general lost. Actually, this happens also when other LOTOS operators, such as enabling or disabling, are used in a recursive context. The purpose of our paper is to study the expressive power of Basic LOTOS in terms of the relations between the syntactical structure and the finite-state behaviour of processes. We then define some sufficient conditions on the syntactical shape of the specifications in order to preserve the finite-state nature, extending those already presented in the literature. Moreover, we define the expressive power of other LOTOS subsets, ranging from context-free processes to Turing-equivalent processes.