Basic observables for processes

A general approach for defining behavioral preorders over process terms as the maximal precongruences induced by basic observables is examined. Three different observables that provide information about the initial communicat ion capabilities of processes and about the possibility that processes get engaged in divergent computations will be considered. We show that the prec ongruences induced by our basic observables coincide with intuitive and/or widely studied behavioral preorders. In particular, we retrieve in our sett ing the must preorder of De Nicola and Hennessy and the fair/should preorde r introduced by Cleaveland and Natarajan and by Brinksma, Rensink, and Vogl er. A new form of testing preorder, which we call safe-must, also emerges. The alternative characterizations we offer shed light on the differences be tween these preorders and on the role played in their definition by tests f or divergence. (C) 1999 Academic Press.