**IFIP
WG 2.2 Meeting Warsaw**

September 20-22, 2010

**Titles
and abstracts of talks**

(in chronological order)

**Speaker:
Stefan Merz
Title: Reduction Revisited: Verifying Round-Based Distributed Algorithms
Abstract: **

Distributed algorithms are often quite subtle, in the way they operate and in the assumptions they make. Formal verification is therefore crucial in distributed computing. To facilitate their design and understanding, many existing distributed algorithms are structured in rounds: each process first sends messages, then receives messages from other processes, and finally makes a local state transition. However, existing formal models of distributed algorithms do not take advantage of this structure, but are based on a fine-grained description of systems whose individual processes are represented by communicating state machines.

Reduction theorems for concurrent and distributed algorithm have been studied
since Lipton's seminal paper in 1975. Broadly speaking, they aim at pretending
that certain sequences of events happen indivisibly, thus allowing verification
to be carried out over coarser-grained models of algorithms and systems. We
revisit this line of research and contribute a reduction theorem for distributed
algorithms that are organized in communication-closed rounds, demonstrating
its benefits on the verification of several consensus algorithms using model
checking and theorem proving.

**Speaker:
Marjan Sirjani
Title: The Coordination Language Reo, its Formal Semantics and Analysis Techniques
Abstract: **

**Speaker:
Naoki Kobayashi
Title: Model-Checking Higher-Order Programs
Abstract: **

**Speaker:
Matthew Hennessy
Title: A Theory of Nondeterministic and Probabilistic Processes
Abstract: **

References:

(1) Yuxin Deng, Rob van Glabbeek, Matthew Hennessy, Carroll Morgan.

Characterising Testing Preorders for Finite Probabilistic Processes, LMCS
(Logical Methods

in Computer Science), 2008

(2) Yuxin Deng, Rob van Glabbeek, Matthew Hennessy, Carroll Morgan.

Testing Finitary Probabilistic Processes, CONCUR 2009

**Speaker:
Christel Baier
Title: Quantitative Analysis of Randomized Systems and Probabilistic Automata
Abstract: **

**Speaker:
Antonin Kucera
Title: Properties of Stochastic Games with Branching-Time Winning Objectives
Abstract: **

Stochastic games are directed binary graphs where each vertex belongs either to Player-I, Player-II, and it is stochastic. The talk surveys recent results about stochastic games with branching-time winning objectives that are specified as formulae of probabilistic branching-time logics such as PCTL or PCTL*. The goal of Player-I is to satisfy a given formula, while Player-II aims at the opposite. Such games are generally not determined, and winning strategies (if they exist) may require both memory and randomization. Still, the winner in such games can be determined effectively in some cases.

(Joint work with Stefan Kiefer and Michael Luttenberger)

T. Brázdil, V. Forejt, and A. Kucera.

Controller Synthesis and Verification for Markov Decision Processes with

Qualitative Branching Time Objectives.

In Proceedings of 35th International Colloquium on Automata, Languages and

Programming (ICALP 2008), pages 148-159, volume 5126 of LNCS. Springer, 2008.

T. Brázdil, V. Brožek, V. Forejt, and A. Kucera.

Stochastic Games with Branching-Time Winning Objectives.

In Proceedings of 21st Annual IEEE Symposium on Logic in Computer Science
(LICS 2006),

pages 349-358, IEEE Computer Society, 2006.

**Speaker:
Joost-Pieter Katoen
Title: Concurrency, Interaction, Abstraction and Randomness
Abstract: **

A key problem in model checking IMCs, in fact stochastic real-time games, is computing maximal time-bounded reachability probabilities. We show a discretisation approach to determine optimal timed (measurable) policies, and report on some practical results.

Finally, we show that IMCs are the semantical backbone for higher-level formalisms
from various domains such as generalized stochastic Petri nets (GSPNs) used
in performance evaluation, dynamic fault trees (DFTs) used in reliability
and safety engineering, and AADL, a standardised language in hardware/software
co-design.

**Speaker:
Jan Rutten
Title: Stream differential equations: theory and applications
Abstract: **

Coinduction has come to play an ever more important role in theoretical computer science, for the specification of and reasoning about infinite data structures and, more generally, automata with infinite behaviour.

In this talk, we shall focus on a recently introduced formalism for coinductive
definitions: behavioural differential equations, with which one specifies
behaviour in terms of initial outputs and behavioural derivatives (next state
operators). Our emphasis will be on the elementary calculus of streams (infinite
sequences), of which we shall

discuss the basic theory, developed in close analogy to mathematical analysis.

As an application area, we will mention a calculus for periodic stream operators.
Using this, we will give a new and transparent proof of Moessner's theorem
using coinduction. This theorem (from 1951 - 1952) gives a suprising construction
for the stream of powers n^k of the natural numbers (such as 1,8,27,64, ...
for k=3) out of the stream of natural numbers by an alternating process of
stream sampling and taking partial sums.

**Speaker:
Peter D. Mosses
Title: On bisimulation and modularity
Abstract: **

In this talk we consider preservation of sound equations for several notions of bisimilarity on open terms: closed-instance (ci-) bisimilarity and formal-hypothesis (fh-) bisimilarity, both due to De Simone [1] and hypothesis-preserving (hp-) bisimilarity, due to Rensink [2].

We give simple examples showing that for ci-bisimilarity, sound equations on open terms are not preserved by disjoint extensions. For both fh-bisimilarity and hp-bisimilarity, arbitrary sound equations on open terms are preserved by all disjoint extensions which do not add labels. Moreover, for slight variations of fh- and hp-bisimilarity, all sound equations are preserved by arbitrary disjoint extensions. See [3] for further details and proofs.

References:

[1] R. de Simone (1985): Higher-Level Synchronizing Devices

in MEIJE-SCCS. Theoretical Computer Science 37, pp. 245â€“267.

[2] A. Rensink (2000): Bisimilarity of Open Terms.

Information and Computation 156, pp. 345â€“385.

[3] P. D. Mosses, M. R. Mousavi & M. A. Reniers (2010):

Robustness of Equations Under Operational Extensions.

Proc. EXPRESS 2010. EPTCS, to appear; preliminary version
available

**Speaker:
Philippe Darondeau
Title: Some Questions about Security and Concurrency
Abstract: **

References:

[1] R. de Simone (1985): Higher-Level Synchronizing Devices

in MEIJE-SCCS. Theoretical Computer Science 37, pp. 245â€“267.

[1]
Supervisory Control for Modal Specifications of Services.

P. Darondeau, J. Dubreil, H. Marchand. Wodes, IEEE (2010) 428-435

[2]
Supervisory Control of Opacity.

J. Dubreil, P. Darondeau, H. Marchand. IEEE-TAC 55(5) (2010) 1089-1100

[3]
On the Decidability of Non Interference over Unbounded Petri Nets.

E. Best, P. Darondeau, R. Gorrieri. 8th International Workshop on Security
Issues in Concurrency (SecCo 2010).

**Speaker:
Maciej Koutny
Title: Step Coverability Algorithms for Concurrent Systems
Abstract: **

**Speaker:
K.V.S Prasad
Title: A pointer to Computational Modeling in Biology
Abstract: **

These languages were derived from systems like the stochastic pi-calculus,
and allow agent- or rule-based descriptions of systems. Several chemical reactions
can be replaced by a single rule that partially specifies the reactants: eg.,
giving the states of only those binding sites relevant to the class of reaction.
Focusing on local aspects helps too: a system of m metals and h halogens,
say, needs not m*h reactions, but just m+h reactions saying for each element
how it forms ions.

**Speaker:
Andrzej Tarlecki
Title: Some nuances of many-sorted algebra
Abstract: **

**Speaker:
Willem Paul de Roever
Title: What is in a Step: New Perspectives on a Classical Question
Abstract: **

**Speaker:
Markus Müller-Olm
Title: Lock-join-sensitive Analysis of Recursive Programs with Thread-creation
Abstract: **

reachability analysis and its applications. Then, we move from a word-shaped
to tree-shaped views of executions which allows us to impose regular constraints
on the communicated actions in symbolic backward analysis or even to describe
the entire set of executions by regular means. This in turn enables us to
do lock-join-sensitive reachability analysis as the set of action trees that
posess a lock-join-sensitive schedule turns out to be regular.

The talk is based on papers presented at CONCUR 2005 and CAV 2009 and ongoing
recent work. It reports on joint work with various people.

**Speaker:
Ernst-Rüdiger Olderog
Title: Layered Composition for Data-Enriched Real-Time Systems
Abstract: **

We investigate techniques that aim at easier verification of data-enriched
real-time systems, modelled as networks of extended timed automata (ETA) running
in parallel. To this end, we reconsider the work of Zwiers and Janssen developed
in the early 1990s on layered composition in the setting of ETA. First introduce
a syntactic notion of independence and an operator for layered composition of
ETA. Under certain independence conditions, the Communication Closed Layer (CCL)
laws are shown to hold for ETA. Next, we introduce input/output (i/o) and partial-order
(po) equivalences, and show that they are preserved when the layered composition
operator is replaced by sequential composition within the CCL laws. Finally,
we demonstrate the effect of layered composition by revisiting a case study
of the UPPAAL model checker for ETA, a collision avoidance protocol developed
for an audio/video system of Bang and Olufsen.

(joint work with Mani Swaminathan)