Combined 19th International Workshop on

Expressiveness in Concurrency

and 9th Workshop on

Structural Operational Semantics

Monday, September 3, 2012
Newcastle upon Tyne, United Kingdom
Affiliated with CONCUR 2012


The EXPRESS workshops aim at bringing together researchers interested in the expressiveness of various formal systems and semantic notions, particularly in the field of concurrency. Their focus has traditionally been on the comparison between programming concepts (such as concurrent, functional, imperative, logic and object-oriented programming) and between mathematical models of computation (such as process algebras, Petri nets, event structures, modal logics, and rewrite systems) on the basis of their relative expressive power. The EXPRESS workshop series has run successfully since 1994 and over the years this focus has become broadly construed.

The SOS workshops aim at being a forum for researchers, students and practitioners interested in new developments, and directions for future investigation, in the field of structural operational semantics. One of the specific goals of the SOS workshop series is to establish synergies between the concurrency and programming language communities working on the theory and practice of SOS. Reports on applications of SOS to other fields are also most welcome, including: modelling and analysis of biological systems, security of computer systems programming, modelling and analysis of embedded systems, specification of middle-ware and coordination languages, programming language semantics and implementation, static analysis software and hardware verification, semantics for domain-specific languages and model-based engineering.

This year the EXPRESS and SOS communities organize a combined EXPRESS/SOS 2012 workshop on the formal semantics of systems and programming concepts, and on the expressiveness of mathematical models of computation.

Invited Speaker

Colin Stirling (University of Edinburgh, United Kingdom)


9.00-10.00: Colin Stirling (invited presentation)
Applying automata and games to simply typed lambda calculus
The application of automata and games to verification of concurrent systems is now well established. In this talk we consider how automata and games can be used to solve decision problems in simply typed lambda calculus.
10.00-10.30: Wojciech Czerwiński and Sławomir Lasota
Partially-commutative context-free languages
The paper is about a class of languages that extends context-free languages (CFL) and is stable under shuffle. Specifically, we investigate the class of partially-commutative context-free languages (PCCFL), where non-terminal symbols are commutative according to a binary independence relation, very much like in trace theory. The class has been recently proposed as a robust class subsuming CFL and commutative CFL. This paper surveys properties of PCCFL. We identify a natural corresponding automaton model: stateless multi-pushdown automata. We show stability of the class under natural operations, including homomorphic images and shuffle. Finally, we relate expressiveness of PCCFL to two other relevant classes: CFL extended with shuffle and trace-closures of CFL. Among technical contributions of the paper are pumping lemmas, as an elegant completion of known pumping properties of regular languages, CFL and commutative CFL.
10.30-11.00: Coffee
11.00-11.30: Marco Giunti, Catuscia Palamidessi and Frank D. Valencia
Hide and New in the Pi-Calculus
In this paper, we enrich the pi-calculus with an operator for confidentiality (hide), whose main effect is to restrict the access to the object of the communication, thus representing confidentiality in a natural way. The hide operator is meant for local communication, and it differs from new in that it forbids the extrusion of the name and hence has a static scope. Consequently, a communication channel in the scope of a hide can be implemented as a dedicated channel, and it is more secure than one in the scope of a new. To emphasize the difference, we introduce a spy context that represents a side-channel attack and breaks some of the standard security equations for new. To formally reason on the security guarantees provided by the hide construct, we introduce an observational theory and establish stronger equivalences by relying on a proof technique based on bisimulation semantics.
11.30-12.00: Stephan Mennicke
An Operational Petri Net Semantics for the Join-Calculus
We present a concurrent operational Petri net semantics for the join-calculus, a process calculus for specifying concurrent and distributed systems. There often is a gap between system specifications and the actual implementations caused by synchrony assumptions on the specification side and asynchronously interacting components in implementations. The join-calculus is promising to reduce this gap by providing an abstract specification language which is asynchronously distributable. Classical process semantics establish an implicit order of actually independent actions, by means of an interleaving. So does the semantics of the join-calculus. To capture such independent actions, step-based semantics, e.g., as defined on Petri nets, are employed. Our Petri net semantics for the join-calculus induces step-behavior in a natural way. We prove our semantics behaviorally equivalent to the original join-calculus semantics by means of a bisimulation. We discuss how join specific assumptions influence an existing notion of distributability based on Petri nets.
12.00-12.30: Gérard Boudol, Gustavo Petri and Bernard Serpette
Relaxed Operational Semantics of Concurrent Programming Languages
We propose a novel, operational framework to formally describe the semantics of concurrent programs running within the context of a relaxed memory model. Our framework features a ``temporary store'' where the memory operations issued by the threads are recorded, in program order. A memory model then specifies the conditions under which a pending operation from this sequence is allowed to be globally performed, possibly out of order. The memory model also involves a ``write grain,'' accounting for architectures where a thread may read a write that is not yet globally visible. Our formal model is supported by a software simulator, allowing us to run litmus tests in our semantics.
12.30-14.00: Lunch
14.00-14.30: Maxim Strygin and Hayo Thielecke
Operational semantics for signal handling
Signals are a lightweight form of interprocess communication in Unix. When a process receives a signal, the control flow is interrupted and a previously installed signal handler is run. Signal handling is reminiscent both of exception handling and concurrent interleaving of processes. In this paper, we investigate different approaches to formalizing signal handling in operational semantics, and compare them in a series of examples. We find the big-step style of operational semantics to be well suited to modelling signal handling. We integrate exception handling with our big-step semantics of signal handling, by adopting the exception convention as defined in the Definition of Standard ML. The semantics needs to capture the complex interactions between signal handling and exception handling.
14.30-15.00: Matias David Lee, Daniel Gebler and Pedro R. D'Argenio
Tree rules in probabilistic transition system specifications with negative and quantitative premises
Probabilistic transition system specifications (PTSSs) in the ntmufnu/ntmuxnu format provide structural operational semantics for Segala-type systems that exhibit both probabilistic and nondeterministic behavior and guarantee that isimilarity is a congruence.Similar to the nondeterministic case of rule format tyft/tyxt, we show that the well-foundedness requirement is unnecessary in the probabilistic setting. To achieve this, we first define an extended version of the ntmufnu/ntmuxnu format in which quantitative premises and conclusions include nested convex combinations of distributions. This format also guarantees that bisimilarity is a congruence. Then, for a given (possibly non-well-founded) PTSS in the new format, we construct an equivalent well-founded transition system consisting of only rules of the simpler (well-founded) probabilistic ntree format. Furthermore, we develop a proof-theoretic notion for these PTSSs that coincides with the existing stratification-based meaning in case the PTSS is stratifiable. This continues the line of research lifting structural operational semantic results from the nondeterministic setting to systems with both probabilistic and nondeterministic behavior.
15.00-15.30: Marcello M. Bonsangue, Stefan Milius and Jurriaan Rot
On the specification of operations on the rational behaviour of systems
Structural operational semantics can be studied at the general level of distributive laws of syntax over behaviour. This yields specification formats for well-behaved algebraic operations on final coalgebras, which are a domain for the behaviour of all systems of a given type functor. We introduce a format for specification of algebraic operations that restrict to the rational fixpoint of a functor, which captures the behaviour of finite systems. In other words, we show that rational behaviour is closed under operations specified in our format. As applications we consider operations on regular languages, regular processes and finite weighted transition systems.
15.30-16.00: Coffee
16.00-16.30: Piotr Hofman and Patrick Totzke
Approximating Weak Bisimilarity of Basic Parallel Processes
This paper explores the well known approximation approach to decide weak bisimilarity of Basic Parallel Processes. We look into how different refinement functions can be used to prove weak bisimilarity decidable for certain subclasses. We also show their limitations for the general case. In particular, we show a lower bound of ω * ω for the approximants which allow weak steps and a lower bound of ω + ω for the approximants that allow sequences of actions. The former lower bound negatively answers the open question of Jančar and Hirshfeld.
16.30-17.00: Maciej Gazda and Tim A.C. Willemse
Expressiveness and Completeness in Abstraction
We study two notions of expressiveness, which have appeared in abstraction theory for model checking, and find them incomparable in general. In particular, we show that according to the most widely used notion, the class of Kripke Modal Transition Systems is strictly less expressive than the class of Generalised Kripke Modal Transition Systems (a generalised variant of Kripke Modal Transition Systems equipped with hypertransitions). Furthermore, we investigate the ability of an abstraction framework to prove a formula with a finite abstract model, a property known as completeness. We address the issue of completeness from a general perspective: the way it depends on certain abstraction parameters, as well as its relationship with expressiveness.
17.00-17.30: Rob van Glabbeek
Musings on Encodings and Expressiveness
This paper proposes a definition of what it means for one system description language to encode another one, thereby enabling an ordering of system description languages with respect to expressive power. I compare the proposed definition with other definitions of encoding and expressiveness found in the literature, and illustrate it on a case study: comparing the expressive power of CCS and CSP.


The workshop proceedings are available as EPTCS 89.


Please register for EXPRESS/SOS 2012 via the registration page of The Newcastle Connection 2012. Deadline for early registration is August 3, 2012.


Bas Luttik (Eindhoven University of Technology, NL)
Michel Reniers (Eindhoven University of Technology, NL)

Programme Committee

Luca Aceto (Reykjavík University, Iceland)
Johannes Borgström (Uppsala University, Sweden)
Ilaria Castellani (INRIA Sophia Antipolis, France)
Sibylle Fröschle (University of Oldenburg, Germany)
Fabio Gadducci (Università di Pisa, Italy)
Bartek Klin (University of Warsaw, Poland)
Bas Luttik (Eindhoven University of Technology, The Netherlands)
Keiko Nakata (Tallinn University of Technology, Estonia)
Michel Reniers (Eindhoven University of Technology, The Netherlands)
Jiri Srba (Aalborg University, Denmark)
Alwen Tiu (Australian National University, Australia)
Frank Valencia (LIX, CNRS & Ecole Polytechnique, France)
Walter Vogler (Augsburg University, Germany)


The EXPRESS workshops were originally held as meetings of the HCM project EXPRESS, which was active with the same focus from January 1994 till December 1997. The first three workshops were held respectively in Amsterdam (1994, chaired by Frits Vaandrager), Tarquinia (1995, chaired by Rocco De Nicola), and Dagstuhl (1996, co-chaired by Ursula Goltz and Rocco De Nicola). EXPRESS'97, which took place in Santa Margherita Ligure and was co-chaired by Catuscia Palamidessi and Joachim Parrow, was organized as a conference with a call for papers and a significant attendance from outside the project. EXPRESS'98 was held as a satellite workshop of the CONCUR'98 conference in Nice, co-chaired by Ilaria Castellani and Catuscia Palamidessi, and like on that occasion EXPRESS'99 was hosted by the CONCUR'99 conference in Eindhoven, co-chaired by Ilaria Castellani and Björn Victor. The EXPRESS'00 workshop was held as a satellite workshop of CONCUR 2000, Pennsylvania State University, co-chaired by Luca Aceto and Björn Victor. The EXPRESS'01 workshop was held at Aalborg University as a satellite of CONCUR'01 and was co-chaired by Luca Aceto and Prakash Panangaden. The EXPRESS'02 workshop was held at Brno University as a satellite of CONCUR'02 and was co-chaired by Uwe Nestmann and Prakash Panangaden. The EXPRESS'03 workshop was co-located with CONCUR 2003 in Marseille and was co-chaired by Flavio Corradini and Uwe Nestmann. The EXPRESS'04 workshop was co-located with CONCUR 2004 in London and was co-chaired by Jos Baeten and Flavio Corradini. The EXPRESS'05 workshop was co-located with CONCUR 2005 in San Francisco and was co-chaired by Jos Baeten and Iain Phillips. The EXPRESS'06 workshop was co-located with CONCUR 2006 in Bonn and was co-chaired by Roberto Amadio and Iain Phillips. The EXPRESS'07 workshop was co-located with CONCUR 2007 in Lisbon and was co-chaired by Roberto Amadio and Thomas Hildebrandt. The EXPRESS'08 workshop was co-located with CONCUR 2008 in Toronto and was co-chaired by Daniele Gorla and Thomas Hildebrandt. The EXPRESS'09 workshop was co-located with CONCUR 2009 in Bologna and was co-chaired by Sibylle Fröschle and Daniele Gorla. The EXPRESS'10 workshop was co-located with CONCUR 2010 in Paris and was co-chaired by Sibylle Fröschle and Frank Valencia. The EXPRESS'11 workshop was co-located with CONCUR 2011 in Aachen and was co-chaired by Bas Luttik and Frank Valencia.

The first SOS Workshop took place in London as one of the satellite workshops of CONCUR 2004. Subsequently, SOS 2005 occurred in Lisbon as a satellite workshop of ICALP 2005, SOS 2006 in Bonn as a satellite workshop of CONCUR 2006, SOS 2007 in Wroclaw as a satellite workshop of LICS and ICALP 2007, and SOS 2008 in Reykjavik as a satellite workshop of ICALP 2008. SOS 2009 was held as a satellite workshop of CONCUR 2009 in Bologna. SOS 2010 was held as a satellite workshop of CONCUR 2010 in Paris. Finally, SOS 2011 was held as a satellite workshop of CONCUR 2011 in Aachen. A special issue of the Journal of Logic and Algebraic Programming on Structural Operational Semantics appeared in 2004; a special issue of Theoretical Computer Science dedicated to SOS 2005 appeared in 2007, and a special issue of Information & Computation on Structural Operational Semantics inspired by SOS 2006-2007 appeared in 2009.

Page maintained by Bas Luttik Last modified: Wed Aug 15 16:17:06 CEST 2012