Summary: Effective Lossy Queue Languages
Parosh Aziz Abdulla 1 , Luc Boasson 2 , and Ahmed Bouajjani 2 ?
1 DoCS, Uppsala University, P.O. Box 325, S75105 Uppsala, Sweden.
Phone: (+46) 18 471 31 63. Fax: (+46) 18 55 02 25.
Liafa, Univ. of Paris 7, Case 7014, 2 place Jussieu, F75251 Paris Cedex 05, France.
Phone: (+33) 1 4427 2841/7819. Fax: (+33) 1 4427 6849.
ICALP'01 submission, TRACK B
Abstract. Although the set of reachable states of a lossy channel system (LCS)
is regular, it is wellknown that this set cannot be constructed effectively. In this
paper, we characterize significant classes of LCS for which the set of reachable
states can be computed. Furthermore, we show that, for slight generatlizations
of these classes, computability can no longer be achieved.
To carry out our study, we define rewriting systems which capture the behaviour
of LCS, in the sense that (i) they have a FIFOlike semantics and (ii) their lan
guages are downward closed with respect to the substring relation. The main
result of the paper shows that, for contextfree rewriting systems, the corre
sponding language can be computed. An interesting consequence of our results