August 27, 2016, Quebec City, Canada
A satellite event of CONCUR 2016
TRENDS 2016 is an event organised by IFIP WG 1.8 on Concurrency Theory. It aims at bringing together researchers interested in Concurrency Theory and its applications to
exchange ideas and discuss recent trends and open problems. The event will take place in the morning of August 27, 2016 and will consist of three invited talks, followed by the yearly WG 1.8 business meeting.
- Franck van Breugel, York University, Canada
- Dana Fisman, Ben-Gurion University, Israel
- Philippa Gardner, Imperial College, UK
9:00-09:45 Invited talk: Franck van Breugel, Towards a Quantitative Theory of Concurrent Probabilistic Systems
For the last three and a half decades behavioural equivalences such as bisimilarity, due to Milner and Park, have been a cornerstone of concurrency theory. As this theory matured, more detailed models of concurrent systems have been developed, some including quantitative data such as cost, probabilities and time. For these models with quantitative information, behavioural equivalences were proposed, such as probabilistic bisimilarity, due to Larsen and Skou. Although these behavioural equivalences allow us to reason about the behaviour of concurrent systems, they have one drawback: they are not robust. That is, small changes in the quantitative data may cause equivalent states to becomes inequivalent or vice versa. Since the quantitative data is usually is obtained experimentally and, therefore is often just an approximation, this lack of robustness is a serious limitation of behavioural equivalences for concurrent systems with quantitative information. This lack of robustness was first pointed out by Giacalone, Jou and Smolka. They suggested generalizing behavioural equivalences, which assign to each pair of states a Boolean, to behavioural pseudometrics, which assign to each pair of states a nonnegative real number. Behavioural pseudometrics play an increasingly important role in concurrency theory, as is reflected, for example, by the fact that four papers on this topic are part of this year’s program of CONCUR.
In this talk, I will focus on behavioural pseudometrics for concurrent probabilistic systems. These systems are often modelled by Segala’s probabilistic automata. During the last decade several behavioural pseudometrics have been introduced for these automata. Here, I will concentrate on the one put forward by Deng, Chothia, Palamidessi, and Pang. I will use this behavioural pseudometric to illustrate two trends. Firstly, I will show how games can be used to characterize and compute behavioural pseudometrics. Secondly, I will show that it is often beneficial to decide the behavioural equivalence before computing the behavioural pseudometric.
9:45-10:30 Invited talk: Dana Fisman, Inferring Regular Languages and omega-Languages
In the last decade the problem of inferring an unknown regular language using membership and equivalence queries, solved by Angluin in 87, has found many application in verification and synthesis, e.g., in black-box checking, assume-guarantee reasoning, error localization, regular model checking, and more. These new applications challenge the state-of-the art solutions in various directions, in particular, scaling or working with more succinct representations, and dealing with omega-languages, the main model for reactive systems.
Inference algorithms typically rely on the correspondence between the automata states and the right congruence, henceforth, the residuality property. DFAs enjoy the residuality property (as stated by the Myhill-Nerode Theorem) but more succinct representations such as non-deterministic and alternating finite automata (NFAs and AFAs) in general do not. The situation in the omega-languages realm is even worse, since none of the traditional automata that can express all regular omega-languages enjoys the residuality property.
In this talk I will survey residual models for regular languages and omega-languages, the simple learning algorithms that can infer these, and many related open questions.
The talk is based on joint works with Dana Angluin, Udi Boker and Sarah Eisenstat.
10:30-11:00 Coffee Break
11:00-11:45 Invited talk: Philippa Gardner, A Concurrent Specification of POSIX
POSIX is a standard for operating systems, with a substantial part devoted to specifying file-system operations. File-system operations exhibit complex concurrent behaviour, comprising multiple actions affecting different parts of the state: typically, multiple atomic reads followed by an atomic update. However, the standard’s description of concurrent behaviour is unsatisfactory: it is fragmented; contains ambiguities; and is generally under-specified. We provide a formal concurrent specification of POSIX file systems and demonstrate scalable reasoning for clients. Our specification is based on a concurrent specification language, which combines a refinement calculus with recent developments in concurrent separation logics for reasoning about abstract atomic operations.
In this talk, I will give an overview of recent work on concurrent separation logics in general and describe our work on the concurrent specification of POSIX in particular. This work is joint with Gian Ntzik and Pedro da Rocha Pinto. Details of our work on concurrent verification can be found at http://psvg.doc.ic.ac.uk/research/concurrency.html.
11:45-13:00 IFIP WG 1.8 Business Meeting (Open to all)
Participation, both to the workshop and to the IFIP WG 1.8 meeting, is open to everybody. For registration, please consult the CONCUR 2016 registration page.
Ilaria Castellani (INRIA Sophia Antipolis, France)
Mohammad Mousavi (Halmstad University, Sweden)
The aims of IFIP WG 1.8 on Concurrency Theory are:
To develop theoretical foundations of concurrency, exploring frontiers of existing theoretical models like process algebra and process calculi, so as to obtain a deeper theoretical understanding of concurrent and parallel systems.
To promote and coordinate the exchange of information on concurrency theory, by sharing ideas, discussing open problems, and identifying future directions of research in the area.
The activities of this WG encompass all aspects of concurrency theory and its applications.
More information on IFIP WG 1.8 can be found on its home page.
The first instalment of TRENDS (TRENDS 2012) was held on September 8, 2012 as a satellite event of CONCUR 2012, in Newcastle upon Tyne, UK.
The second instalment of TRENDS (TRENDS 2013) was held on August 31, 2013 as a satellite event of CONCUR 2013, in Buenos Aires, Argentina.
The third instalment of TRENDS (TRENDS 2014) was held on September 6, 2014 as a satellite event of CONCUR 2014, in Rome, Italy.
The fourth instalment of TRENDS (TRENDS 2015) was held on September 6, 2015 as a satellite event of CONCUR 2015, in Madrid, Spain.