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

2. 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)

3. 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

4. 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)

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

6. 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 +

7. 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 +