Process Algebra (2IF45) Extending Process Algebra: Abstraction Dr. Suzana Andova

System specification manipulation (recap) reduction on specification components’ specifications reduction on specification the whole system specification composition by axiom simpler smaller in a particular form (basic) … reduction on LTSs the state space SOS rules Process Algebra (2IF45)

TCP language extended with hiding feature TCP(A, ) A is a pre-defied set of atomic actions internal (silent) action ,   A  is a pre-defined communication function Signature: (constructs of the language) constants 0,1 action prefix a._ non-deterministic choice _+_ sequential composition _  _ hiding operator I for I  A Process behaviour specification described by process equations, guarded recursive process variables and guarded process specifications equivalence relation that treats  differently parallel composition _ || _ communication composition. _ | _ encapsulation H(_), where H  A

Towards  equivalence relation(s) Think about different ways to reduce these processes? hiding  reducing ? in50c   in1euro in50c !coffee !coffee !coffee !coffee hiding reducing ? 50c 40c   !coffee !tea !coffee !tea Which reduced process preserves “the same moment of choice” as in the original process with s? Process Algebra (2IF45)

Towards  equivalence relation(s) reducing hiding ? insert insert 40c  coffee coffee reducing hiding ? insert insert  coin card  coffee coffee Process Algebra (2IF45)

Towards our equivalence relation -Conclusions Some internal steps cannot be removed. Some internal steps can be removed. They are called inert! Inert internal steps occur in following situations: … … reduces to a a Q  P P + + Q P +

Towards our equivalence relation -Conclusions Some internal steps cannot be removed. Some internal steps can be removed. They are called inert! Inert internal steps occur in following situations: Relation to be established is: … … reduces to a a Q  P P + + Q P +