Luca de Alfaro in the News

At CONCUR 2007, I learned that our colleague and member of WG1.8 Luca de Alfaro has recently hit the news for his work on an evaluation of trust in contributions to Wikipedia. (See Demo: Coloring the text of the Wikipedia according to its trust.) Luca's work is based on the idea of colouring the text of Wikipedia articles according to a computed value of trust. The trust value of each word of a Wikipedia article is computed as a function of the reputation of the original author, as well as the reputation of all authors who subsequently revised the text.

This work of Luca's was mentioned in the Washington Post (I cannot locate the link anymore), the Jerusalem Post, ACM TechNews and SFGate.com amongst others.

Luca will also be the PC chair for FOSSACS 2009 in York, but this will give him less media exposure :-)

Nadia Busi (1968-2007)

During the excursion for CONCUR 2007, while visiting the Arrábida Convent, we were hit by the sad news that our colleague and friend Nadia Busi had suddenly passed away the night before. A paper having Nadia as one of the authors had been presented at the conference just before we set off for the excursion.

Our community has lost a very active and creative researcher, a woman who could be an example for others to follow and, above all, a very kind human being.

An obituary for Nadia, written by Roberto Gorrieri, will appear in the October issue of the BEATCS. You can read it here.

"We are such stuff
As dreams are made on, and our little life
Is rounded with a sleep."
(Shakespeare, "The Tempest")

Guest Post from Jorge Perez

I received this contribution from Jorge Perez, and post it with pleasure.

I have found your reports on the WG1.8 Workshop extremely enlightening. I am specially impressed by the invited speaker's opinions on the role of probabilistic/stochastic modeling. In my opinion, and having little experience on the theoretical side of the topic, their positions are, at the very least, certainly a matter for debate.

The topic of the workshop also made me remember of the spirit of my former research group in Colombia. For many reasons, the group (called AVISPA, see http://avispa.puj.edu.co/) is interested essentially in applied concurrency. This means thinking at the same time in theory and usable applications, beyond prototypes. Perhaps the most successful application area has been Computer Music.
In collaboration with the French Acoustics/Music Research Institute (IRCAM), AVISPA has designed and implemented formal, concurrent languages to assist music composers in their duties. I know this is not properly an 'industrial application' but it could be an example of how concurrency theory can be fruitfully applied.

AVISPA has recently launched a project on applied concurrency: it is
called REACT (see
http://cic.puj.edu.co/wiki/doku.php?id=grupos:avispa:react), and it aims at consolidating our concurrency languages in several application areas, including security, systems biology, computer music (or more generally: multimedia semantic interaction).

Sorry for the long post, but the topic is very interesting for me and I wanted to share this (perhaps unusual) approach to applied concurrency.

Some Answers By the Workshop Speakers

In a previous post, I listed the questions that the attendees at our CONCUR 2007 workshop raised to the invited speakers and panel members. I also promised to pen down my recollections of their answers. Here they, hoping that I won't misrepresent the opinions of these colleagues too much. I am sure that they will correct me if I inadvertently do so. Anything I write below should be taken with a huge pinch of salt :-)

What is the role/importance of real-time in modelling? Does industry want dense-time or discrete-time models?

Kim G. Larsen (KGL): The vast majority of computing systems in operation today are embedded. Proper modelling and analysis of the behaviour of embedded systems requires time. However, industry does not really seem to care whether the model of time used in the models is discrete or continuous. When analyzing embedded systems, quantitative analysis techniques are needed and I expect that stochastics will play an increasing role in the future.

Jan Friso Groote (JFG): Basically, industry do not know what they want and there is little point in chasing their ever-changing needs. Concrete modelling and analysis of computing systems should be based on a uniform calculus, which is rich enough to model the problem scenarios at hand. As far as real-time is concerned, it should be expressible in the uniform calculus.

How does one involve small- and medium-size companies in collaborations with concurrency theoreticians/practitioners? Does "company size" matter?

Both JFG and KGL reported on several examples of interaction with industry where there seemed no relation between "size" and the success of the interaction. Kim described a successful collaboration on testing of GUI applications with a one-person company having basically no technological expertise. This was compared with the collaboration with Bang and Olufsen, which was a failure despite the resounding success of their first cooperation.

Jan Friso highlighted the successful cooperations with industry within the Laquso project. (See here for more information.)

Hubert Garavel (HG) stated there are three necessary conditions for a successful collaboration with industry. The company should have

1. a strong interest in quality,
   
2. a lot of money and
   
3. a formal modelling group in house.
   

These criteria are difficult to find in a small- or medium-size company. In particular, the third criterion above is useful because it opens up the possibility of embedding a company engineer within the academic research group.

Is there any need for stochastic and probabilistic modelling in applications? More pointedly, have you met an example that you could not model because your tool does not support stochastic or probabilistic phenomena?

There seemed to be a general opinion here that probabilistic modelling is nice, but not necessary. More precisely, none of the speakers had yet met an example that they could not model adequately because their models and tools do not permit stochastic or probabilistic modelling.

JFG stated that he wants to work on research topics that can have applicability in real-life scenarios. He wants to have interaction with industry mainly as a way to learn what are the good/bad aspects of his modelling language and his tools. He feels that one should push for the use of the same model for verification and performance evaluation. (I have a vague recollection that this opinion was also shared by Kim.)

How can we, as a community, foster the building of industrial-strength tools based on sound theories?

The general feeling amongst the panelists was that our community does not have the infrastructure to support tooling efforts. HG pointed out how the situation is better in France, where the development of tools and languages is supported and recognized by institutions like INRIA. (My note: In hindsight, this is reflected by the success of long-term efforts like those that led to Esterel, Coq and CAML, amongst others.)

The panelists suggested that conferences and journals should be keener to accept tools and case studies as refereed contributions on a par with papers. JFG pointed out that Science of Computer Programming has now a track devoted to "expositions on implementations of and experiments with novel programming languages, systems and methods." The journal's web page also states that "It must be emphasized that papers describing new software tools of relevance to SCP are welcome under the strict condition that the source code of the tools is open." KGL also stated that the TACAS conference series was initiated precisely to give more visibility to tooling efforts in our community.

For a one-slide viewpoint on the economics of tool development look at slide 72 of Kim's presentation at the workshop.

What has concurrency theory offered industry so far? What are the next steps that the concurrency community should take in order to increase the impact of its research in an industrial setting? And what are future promising application areas for concurrency research?


JFG: Theory does not have much to offer to industry. We should probably view concurrency theory as a nice mathematical theory that need not have any real-world application.

As for what is it that we can do as a CONCUR community to assist in the work on tools, JFG's answer is to organize that as many students are being taught their use and effective application as possible. One of the biggest problems that we are facing is that far too few people in industry understand what formal methods and their tools can effectively bring to industry. To be on the safe side, they do not see where the techniques are effective and what they offer. They however understand that there are other pressing needs to invest time in.

If we teach formal methods we should teach the most advanced ones that the students can swallow. If they understand the advanced methods they can apply the more straightforward techniques. Of course the reverse does not hold. Don't teach them UML and expect them to understand mCRL2. But if you teach them mCRL2, they will not have any conceptual difficulty to apply UML.

KGL: We should make our techniques fit into the whole system-development process. We should also make sure that existing model-based tools that are already in use by industry have much stronger semantic foundations.

HG: Our community is in trouble! The model of concurrency that is prevalent is industry is Java-like (threads and shared variables). Our foundational beliefs are exotic for industry and message-passing, as used in our process calculi, is not the order of the day. Our major challenge is in pushing the clean model of concurrency we like. Every computer science department in every university should play its part in achieving this aim. Education is one of our best weapons to make industry accept our models and the techniques based upon them.

Concurrency Column for October 2007

I have just posted the piece that will appear in the concurrency column for the October 2007 issue of the BEATCS. The article, authored by Sergio Maffeis, is entitled Dynamic Web Data and Process Calculi and reports on the use of concepts and techniques from process calculi in the study and analysis of dynamic data.

Enjoy it.

Rance Cleaveland's Answers

It is a great pleasure for me to post some answers by my old mate Rance Cleaveland to the questions raised at the CONCUR workshop. Thanks to Rance for sharing his experience with us!


What an interesting workshop; I deeply regret not being able to attend.

At Luca's gentle suggestion ;-) I thought I would have a go at questions he posed at the end of his post.


What is the role/importance of real-time in modelling? Does industry want dense-time or discrete-time models?


In my experience with Reactis, my company's testing and verification tool, Reactis customers absolutely need real-time support. This is due to their applications, which are in automotive and aerospace and develop embedded control software. The most widely used commercial modeling languages (Simulink, Stateflow, SCADE) also include real-time as an intrinsic part of their semantics.

Ironically, given the sound and fury in the academic community, the industrial people I have interacted with for the most part do not care whether time is discrete or continuous. Sometimes, I have encountered customers who want to do hybrid-systems style modeling, and for these people continuity is important.


How does one involve small- and medium-size companies in collaborations with concurrency theoreticians/practitioners? Does "company size" matter?



Regarding SMEs (small- and medium-size enterprises ... a common acronym among US policymakers): I think the best way to involve them is via projects funded by third parties (governments, or a large partner). SMEs generally don't have the overheads to support "blue-sky" research, and their investment-return horizons are necessarily of shorter duration. At both Reactive Systems and Fraunhofer, our concurrency-oriented SME collaborations have either involved collaborations on government research grants or project work on behalf of larger customer. In the latter cases, it was important that we work in commercial notations (e.g. Simulink) rather than research-oriented ones.

Large companies do have resources to put into more basic research, but there is another phenomenon to be aware of: researchers in these companies often view outside researchers as competitors for their internal research funds. So collaborations with these organizations are highly dependent on the personal connections between company and non-company researchers. So-called "business unit" personnel are often the easiest to deal with, but in this case there needs to be a clear, typically short-term, pay-off to them for the collaboration.


Is there any need for stochastic and probabilistic modelling in applications? More pointedly, have you met an example that you could not model because your tool does not support stochastic or probabilistic phenomena?


We support simple probabilistic modeling in Reactis in the form of probability distributions over system inputs that we sample when creating tests. This feature, however, is almost never used by our customers. The reasons for this mostly boil down to a lack of training these engineers receive in stochastic modeling and control, which in turn is tied into the lack of good (or maybe standard) theory for stochastic differential equations.

More precisely, the engineers in automotive and aero that I've dealt with are usually mechanical or electrical engineers with backgrounds in control theory. The feedback control they use relies on plant models (i.e. "environments") being given as differential equations, which are deterministic. The plant models they devise for testing their control-system designs often have parameters that they tweak in order to test how their ideas work under different conditions.

These engineers talk in the abstract about how useful it would be to develop analytical frameworks for probabilistic plants, but tractable theories of probability spaces of differential equations are unknown, as far as I can tell.


How can we, as a community, foster the building of industrial-strength tools based on sound theories?


To have an industial following, tools have to work with languages that industry uses. For most research tools this is a problem, because the input languages are typically invented by the tool developers.

I see two possibilities. One is to work on commercial languages such as Simulink. These languages are often a catastrophe from a mathematical perspective, but they also usually contain subsets that can be nicely formalized for the purposes of giving tool support. If tools have a nice "intermediate notation" into which these cores can be translated, then this offers a pathway for potential industrial customers to experiment with the tools.

The second approach is to become involved in standardization efforts for modeling languages. UML 2.0 has benefited to some extent from concurrency theory, but there are many aspects of that language that remain informal and imprecise.


What has concurrency theory offered industry so far? What are the next steps that the concurrency community should take in order to increase the impact of its research in an industrial setting? And what are future promising application areas for concurrency research?


I think the best way to answer first question is to "trace backward" from commercial tools / modeling languages that have some basis in concurrency. Such tools would include those based on Statecharts (Stateflow, STATEMATE, BetterState); others based on Message Sequence Charts (Rational Rose, other UML tools); the French synchronous-language tools (SCADE, Esterel); tools that include model checkers (the EDA = "electronic design automation" industry); tools that use model-checking-base ideas for other analyses (Reactis, DesignVerifier).

Unfortunately the process-algebra community has had relatively little impact on commercial tool development. This is not due to shortcomings in the theory, in my opinion, but in the inattention that compositionality continues to receive in the (non-research) modeling community. In my experience, event-based modeling is also relatively uncommon, at least in auto and aero: sampling of "state variables" is the preferred modeling paradigm.

I personally would like to see work on semantically robust combinations of specification formulas (e.g. MSCs + state machines, or temporal logic + process algebra) and related tools; theoretically well-founded approaches to verifying systems that use floating-point numbers; and compositional, graphical modeling languages (lots of work done already, but still no commercial interest).

Moshe Vardi's Answers

Moshe Vardi has kindly sent me some brief answers to the questions I posted yesterday. I post them here in order to foster further discussion, and thank Moshe for his contribution.

• What is the role/importance of real-time in modelling? Does industry want dense-time or discrete-time models?

Moshe: Complex hardware designs today are locally synchronous, but globally asynchronous. Using multiple clocks to specify temporal properties is very
important, but I personally saw, so far, no application that required
dense-time reasoning. (Perhaps timing analysis of circuits requires dense
time?)

• How does one involve small- and medium-size companies in collaborations with concurrency theoreticians/practitioners? Does "company size" matter?

Moshe: Large companies can afford to think longer term and invest in internal/external research. This is quite harder to do with small companies, which typically looks for immediate solutions to their problems.

• Is there any need for stochastic and probabilistic modelling in applications? More pointedly, have you met an example that you could not model because your tool does not support stochastic or probabilistic phenomena?

Moshe: I have not seen it so far, but I do hear people starting to talk about probabilistic behavior of computer circuits. Perhaps we'll see a growing need for stochastic modeling in a few years.

• How can we, as a community, foster the building of industrial-strength tools based on sound theories?

Moshe: Academia can rarely build industrial-strength tools. Academic tools are
often the work of a single graduate student. Industry can put several PhD-level people on a single project.

• What has concurrency theory offered industry so far? What are the next steps that the concurrency community should take in order to increase the impact of its research in an industrial setting? And what are future promising application areas for concurrency research?

Moshe: IMHO, the biggest successes of the concurrency-theory community, broadly
conceived, is model checking and the development of synchronous languages. At the same time, many research direction in concurrency theory, such as process calculi and bisimulation theory have had fairly minimal impact. The theory community is often attracted to research based on its theoretical appeal, which does not always correlate with its industrial applicability. This does not mean that industrial applicability should be the guiding principle of research. Nevertheless, it would be worthwhile to pause once in a few years and examine the potential applicability of
theoretical research.

Report on the WG1.8 Workshop at CONCUR 2007---Part 1

Preface

As you may know, Jos Baeten, Wan Fokkink, Anna Ingolfsdottir, Uwe Nestmann and I organized a Workshop on Applying Concurrency Research in Industry, co-located with CONCUR 2007 in Lisbon, on behalf of WG1.8. The workshop was held on the afternoon of Friday, 7 September, and ran concurrently with the last two sessions of the main conference. Despite the competition with CONCUR, we had about 25 participants at the workshop, including several members of the working group. I think that this was a rather decent level of attendance for a "strategic event".

In this post, for the benefit of the WG members and of the community as a whole, I'll try to summarize the main discussion points that were raised during the presentations at the workshop and the ensuing panel discussion. I will also try to recall some of the questions that the audience asked the panel members. I hope that some of blog readers will want to contribute their opinion on these points and give their own answers to those questions themselves.

The organizers of the workshop will use all of the contributions that they'll receive in putting together an article for the concurrency column of the BEATCS.

Report on the Invited Talks

Note: I encourage the speakers to correct anything they said that I may have misinterpreted or misrepresented. I take full responsibility for any error I might have made in relaying the gist of the invited talks, and I'll be happy to post corrections and further comments. This is meant to be a live repository.

The workshop began with four invited presentations delivered by Hubert Garavel, Vincent Danos, Kim G. Larsen and Jan Friso Groote.

Hubert gave an overview of his twenty-year work on the CADP tool set, which is the oldest concurrency-theoretic tool still in activity. A thread underlying his work in what he called "applied concurrency theory" is that one must push the main results of our research area to industry and that this is only possible with the development of strong tool support for our methods. Hubert said that one of his design principles has been to restrict the tool's functionality for efficiency reasons, and that elegant semantics and efficient execution are two separate (at times conflicting) issues.

I have a note to the effect that, during Hubert's presentation, somebody (possibly Hubert himself) said that a lot of code doing bisimulation minimization has been lost over the years. We simply have not been consistent enough in preserving some of our earlier tooling efforts for the present generations of developers. Jan Friso said that current bisimulation minimization algorithms do not scale up to the size of the systems that are currently being analyzed, and asked whether it would be appropriate to rekindle research and implementation efforts on efficient and scalable bisimulation algorithms.

Earlier that day, Vincent had delivered an inspiring tutorial on his work in doing rule-based analysis of biological signalling. Listening to his tutorial, I was left with the impression that he is really having an impact in the life sciences, and that experimental biologists might very well use his tools based on concurrency-theoretic ideas. At the workshop, Vincent presented another way in which concurrency-theoretic ideas can help experimental biologists in their work. Experimental biology has a huge knowledge representation problem. (Vincent mentioned that there are two papers published in that area each minute!) In his opinion, experimental biologists can/should

• use concurrency-inspired languages to express biological understanding and
  
• display this information in a wiki-type system.
  

This will allow them to construct models systematically and to simulate them (exploiting the executable nature of concurrency-theoretic models) well beyond what is possible today by means of experiments.

Kim's talk was based on his experience with the ten-year development of the Uppaal tool, and reported on the knowledge transfer activity, which is part of his involvement in CISS. Apart from surveying the development of Uppaal and its recent offsprings, Kim's talk sent out the following general messages to the audience.

• Tools are a necessary condition for the successful transfer of concurrency-theoretic ideas in industry. Tool development is labour intensive, and one needs the sustained effort of many people over many years to produce good software tools.
  
• Academic courses offered to students and to industry practitioners play a key role.
  
• Concurrency researchers should try and target different communities of potential users. One never knows where successful applications are going to stem from.
  
• A good beginning is useful! Being able to start with a success story may lead to further successes and a long-term collaborations. However, Kim warned against assuming that a good beginning is a guarantee of a good ending, and recounted the story of the Aalborg collaboration with Bang and Olufsen, who disappeared from sight after Klaus Havelund, Arne Skou and Kim found and fixed a bud in one of their protocols. See here.
  
• The success of CISS shows that several companies are very interested in applying concurrency-theoretic ideas and tools because this reduces time to market and increases the quality of their products.
  
• The impact of one's work on the application of concurrency-theoretic research in industry is not always directly proportial to the amount of effort one puts into the work itself. Kim gave the example of the synthesis of control software controlling the temperature and humidity in an actual pig stable in Denmark. This software was synthesized using Uppaal Cora in a short time and is actually running to the satisfaction of its customers :-)
• Finally, Kim called for an expansion of the use of concurrency theory. We should link our work to testing, optimization etc. and embed it into standard software engineering methodologies, which are familiar to practitioners.
  

Jan Friso presented an overview of the mCRL2 tool set, and gave a demo of several features of the system. He stated his belief that proving the correctness of systems by hand gives one understanding that mere button-press model-checking does not yield. However, one needs tools to transfer knowledge to industry and to validate one's manual verifications. He also shared Hubert's belief that the initial emphasis on abstract data types in CADP and muCRL2 was a mistake, but that formalisms supporting data are necessary in applications. One of Jan Friso's messages was that high-performance in tools is underestimated, and that achieving it requires a lot of subtle work. Jan Friso also stressed the importance of teaching courses to our students that involve modelling and analysis of real-life industrial case studies. In that way, when students go and work in industry they will know that there are effective modelling languages and tools that they can use efficiently to check their designs before implementing them. He also stressed the importance of visualization tools.

Some Questions to the Speakers

Here are some questions that were addressed to the speakers during the panel discussion, in no particular order. I encourage readers of this report to post their own answers and further questions as comments to the post. Later on, I will post the answers from the panel members as I recall them.

• What is the role/importance of real-time in modelling? Does industry want dense-time or discrete-time models?
• How does one involve small- medium-size companies in collaborations with concurrency theoreticians/practitioners?
• Is there any need for stochastic and probabilistic modelling in applications? More pointedly, have you met an example that you could not model because your tool does not support stochastic or probabilistic phenomena?
• How can we, as a community, foster the building of industrial-strength tools based on sound theories?
• What has concurrency theory offered industry so far? What are the next steps that the concurrency community should take in order to increase the impact of its research in an industrial setting?

I hope that you will contribute your own questions to the above list and share your answers with the rest of the community via this blog. I will soon post some of the answers given by our panel at the workshop.

Addendum 14/9/2007: After I wrote this post, it occurred to me that the workshop discussion may have given the impression that industrial impact can solely be achieved by means of tools and joint case studies. Moshe Vardi's work on specification languages like ForSpec on the other hand indicates that the development of theoretically sound and clean specification languages that are actually used by industry is another area in which in the community can (and I believe should) have an impact.
I hope I can quote Moshe as saying
"In fact, I believe that much of my industrial impact has been achieved through the development of clean and useful theory."

CALCO Report, Part 3

This is the third, and final, installment of the coverage of CALCO 2007 on this blog. Thanks again to Mohammad for providing reports on the first three days of the event.

The first talk on Thursday was an invited address by Barbara König. Barbara's talk gave an excellent introduction to the general ideas and results on an active area of research in concurrency theory, namely the problem of deriving labelled transition system semantics and bisimulation congruences from reduction semantics and rewrite rules. This is a line of research that has been motivated by the theory of bisimulation congruences for process calculi, most notably the pi-calculus, and where categorical techniques play a fundamental role. See, for instance, the work by Leifer and Milner, and that by Sassone and Sobocinski.

Thursday also featured some talks on modal and epistemic logics, two talks on Chu spaces, and several categorical talks, which were alas well beyond my understanding of category theory.

The invited talk on Friday was delivered by Luis Caires, one of the prime movers behind the development of spatial logics. Luis' talk introduced a logical approach to the semantics of types for concurrency and to their soundness proofs based on spatial logics. I found the ideas presented in Luis' talk very intriguing, and I am going to read his paper in the proceedings when I have some time on my hands.

The conference concluded with a session on process algebra, where both Mohammad and I gave talks. (It is not for me to comment on how successful we were :-)) In case anybody is interested, the slides for my talk are here.

I enjoyed my trip to lovely Bergen, and thank the organizers for a very well-organized event. I hope to be able to visit Bergen again in the future. You can see some photos from Bergen here. Eventually, photos from CALCO will be available here.

Let me conclude with a couple of quotes from talks given at the conference and a poem I saw engraved in Vaagsallmenningen in Bergen.

"If you spell out this definition set theoretically, it looks quite horrible, but is not so difficult." (Clemens Kupke)

"The real voyage of discovery consists not in seeking new landscapes, but in having new eyes." (Marcel Proust, cited by Radu Mardare)

"Hele sit liv,
Anicet,
skal et menneske
laere at leve.
Hele sit liv,
Anicet,
skal han og
laere at doe."

(This roughly means "All his life, Anicet, a man must learn how to live. All his life, Anicet, he must also learn how to die.")

CALCO Report Part 2

Here is the second report from CALCO authored by Mohammad. Enjoy!

Live Report from CALCO - Part 2 Without further ado, here is my second report from CALCO. I will only give a short report of the two interesting keynote talks presented yesterday and today.

• Tuesday: Tuesday was the first day of CALCO 2007 main conference. There were some 40-50 participants (depending on when the snapshot is taken). Till Mossakowki opened the conference by mentioning that, despite initial doubts, CALCO 2007 was indeed a success and it attracted some 57 submissions from 3 continents and 14 countries.

  Stephen Bloom gave the keynote speech of Tuesday on algebraic and regular words and trees formalized as continuous $\Sigma$-algebras. He mentioned a recent result of his together with Zoltan Esik (I&C, 197(1-2):55--89, 2005) in which they present a complete axiomatization for regular words modulo isomorphism. He quoted the following interesting statement from his teacher who taught him about ordinals.

  "Ordinals are the numbers you use to count apples."

• Wednesday: Glynn Winskel delivered his keynote address on symmetry and concurrency. He motivated the choice of the topic by a few examples from Petri Nets and HD Automata and Strand Spaces to the effect that the lack of a notion of symmetry blocks universal treatment of some constructions (such as unfolding). He started off by introducing event structures (surprise, surprise!) and presented their application as types (in stable domain theory) and processes (in the semantics of process algebras and Petri Nets). Subsequently (total, rigid, and open) maps on event structures were presented as ways of relating them and in particular open maps are underscored as a notion of bisimulation among event structures. Semantics of nondeterministic dataflow programs was presented as a challenge to which event structure with some sort of maps to input and output even structures, called stable spans, provide a solution. Glynn mentioned that this is the same as the idea of pro-functors, but admittedly I could not appreciate the value of this fact! After some discussion on insufficiency of stable maps, he defined an abstract notion of symmetry using (a pair of) open maps on event structures. He ran a bit out of time and could not get into concrete applications of this notion of symmetry but the moral of the story, if I understand it correctly, is that by taking symmetry into account you get more general and universal constructions (maps) that are not too fine to distinguish between symmetric objects.

To conclude my reports on CALCO, I feel obliged to thank the local organizer for the excellent organization. Luca arrived here on Wednesday afternoon and I guess we will all have the chance to read about the rest from him.

Live Report from CALCO 2007 - Part 1

This is a guest post provided by MohammadReza Mousavi. Thanks to Mohammad!

Luca kindly invited me to write a guest post in his blog on CALCO 2007: the 2nd Conference on Algebra and Coalgebra in Computer Science. It is hosted by the University of Bergen in the picturesque city of Bergen (a UNESCO world heritage sight).

I am currently sitting in CALCO-jnr, a workshop of CALCO dedicated to young researchers (mainly Ph.D. students). The CALCO-jnr workshop is being attended by some 35 participants and I find the talks quite interesting and for such a workshop, which is usually meant for work-in-progress type of presentations, of reasonably high quality.

I must admit that the more categorical talks go well beyond my knowledge of this field and thus, I just write a few sentences about the few talks that I could (partially) follow.

• Ichiro Hasuo (a bright young researcher from Kyoto University, currently on leave to do a Ph.D. with Bart Jacobs) presented a very interesting talk on the application of Microcosm principle in Concurrency Theory. The Microcosm principle states that there is an analogy between the structure of the outer world and that of its elements (and in particular, that of the inside world of a human being; see this for an application in mathematics). Ichiro (together with Bart Jacobs and Ana Sokolova) take this idea into Computer Science and use it to prove properties such as congruence of behavioral equivalences (specified by the final model of the co-algebra under consideration) and commutativity and associativity of the operators under consideration. If I understand it correctly, they define a natural transformation that maps the composition operator at the level of co-algebras (e.g., LTSs) to the semantics of the composition of the objects in the carrier of the co-algebra (e.g., sets of pairs of processes indexed with labels). A concrete and tangible application is the way the semantics of parallel composition is defined by the synchronization scheme. Their approach resembles the bi-algebraic approach to operational semantics (e.g., this). A more detailed account of their results is available from here.
• Alexandra Silva presented some thoughts on representing bi-infinite streams, i.e., sequence of the form "... a_{-1} a_{0} a_{1} ..." using other worked-out co-algebraic frameworks for infinite binary trees and infinite streams. I remember a very interesting and accessible talk of Jan Rutten in FMCO 2003 presenting the very interesting co-algebraic treatment of streams which resembles the algebraic analysis techniques we learned in high school. Jan will give a talk on a related topic tomorrow, so you may get to read more about it soon.
• Liam O'Reilly talked about CSP-CASL-Prover which is based on a framework combining CSP as the process language and CASL for algebraic specification (of data types) and thus combines process specification and data specification. Their framework is built upon other tools, namely CSP Prover, which allow for reasoning about CSP processes with CASL data types in Isabelle. Coming from Eindhoven, I wonder whether this type of work can be seen as a rival to mCRL2 toolset and if so, which one will be favored in the long run.

In the afternoon, there were two parallel sessions: the continuation of CALCO-jnr and CALCO-tools. I decided to attend the tool presentations and here is a summary of what I learned there.

• Francisco Duran talked about the Maude tool environment. He introduced several tools built around Maude, including Interactive Theorem Prover, Termination Tool, and the Real-Time Maude Tool. Interestingly, a number of these tools have a web interface. There is a recent book on Maude, which can be bought from here.
• In the second talk, Dorel Lucanu introduced CIRC which is a tool for proving behavioral equivalences among (possibly infinite) processes specified in Maude.

So much for my first day of CALCO in Bergen; we will be off to a medieval castle for the reception this evening. Stay tuned for the second report!

Greetings from Bergen.

Being An Active Scientist at Age Eighty

Last Wednesday morning I took an hour to go and listen to a talk by Sigurdur Helgason at the University of Iceland. Sigurdur Helgason is one of Iceland's foremost scientists and a mathematician of great distinction, or so I am told. Suffice it to say that the American Mathematical Society have agreed to publish his collected works by some time next year---a honour that is bestowed only to true giants in mathematics.

I had the pleasure to meet Sigurdur Helgason in June 2004, when Anna and I visited Boston and MIT for Kári Ragnarsson's PhD graduation. He struck me as a very lively, curious and laid-back guy, who still enjoyed life, teaching his courses and thinking about maths despite being well over 70.

Sigurdur Helgason's talk kicked off a conference in honour of his 80th birthday. I had no chance of appreciating the technical content of the talk, but it was remarkable to see a 80-year-old man deliver such a well-planned presentation, reporting on some results he seemed to have achieved over the last four years or so. That was a truly awesome thing to witness.

What I found unbecoming was that there were no questions from the audience after the talk. Maybe the tradition in his area of maths is different from the one in TCS, but I would have expected at least the session chair to ask a token question to that great man.

Fortunately, being 80 and famous, he did not seem to be bothered!

Third ICE-TCS Theory Day

Last Friday, ICE-TCS hosted its third theory day. The programme for the event may be found here.

This year's theory day featured an inaugural professorial address delivered by Magnús M. Halldórsson, who joined my department at Reykjavík University on August 1. The addition of Magnús to our academic staff will substantially strengthen our research profile.

At the theory day, Magnús gave a talk in which he presented approximation algorithms for optimization problems when the objective function is unknown. The aim of the work he discussed during his presentation is to obtain algorithms that are guaranteed to perform reasonably well for all objective functions in the given class. He focussed on cost functions that are monotonic and concave (or, more generally, sub-additive), and presented approximation algorithms whose approximation ratio is 4 for concave functions and 6 for sub-additive ones.

Thomas Erlebach from the University of Leicester continued the "approximation theme" with a talk on network discovery problems. The work Thomas presented in his talk aims at discovering information about an unknown network (modelled as a connected undirected graph) or on verifying the correctness of network information. Thomas discussed two query models. In the former, a query at a node returns all the shortest path trees rooted at that node. In the latter, the result of a query at a node is the collection of shortest-path distances from that node. For the former type of queries, Thomas presented, for instance, a randomized O(sqroot{n log n})-competitive algorithm. For the latter query model, there is a deterministic Omega(sqroot{n}) lower bound and a randomized O(log n) lower bound. Much more can be found in the paper

Zuzana Beerliova, Felix Eberhard, Thomas Erlebach, Alexander Hall, Michael Hoffmann, Matus Mihalak, L. Shankar Ram:
Network Discovery and Verification
IEEE Journal on Selected Areas in Communications, Vol. 24, No. 12, December 2006, pp. 2168-2181. Special issue on Sampling the Internet: Techniques and Applications.

The afternoon session was devoted to a one-hour talk by Tommi Sottinen, our new recruit in financial mathematics, and to two 25-minute talks by Silvio Capobianco and MohammadReza Mousavi. Tommi gave an accessible introduction to the mathematics underlying financial mathematics and the Black-Scholes model. Silvio reported on recent joint work with Patrizia Mentrasti and Tommaso Toffoli, and showed us how to convert certain types of cellular automata to lattice gases. Mohammad wound up a nice scientific day by giving an accessible introduction to some recent work of his aiming at a unified framework for functional and performance analysis of processes. He proposed an approach enabling a provably sound transformation from some existing stochastic process algebras, e.g., PEPA and MTIPP, to a generic form in the mCRL2 language.

This workshop marks the beginning of a very busy year for ICE-TCS, a year leading up to ICALP 2008 in Reykjavík. I hope to see you in Reykjavík for that conference!

Atle Selberg (1917-2007)

The AMS news page reports that the Norwegian mathematician Atle Selberg passed away on August 6. As the AMS news item states, Selberg is perhaps best known for his work on the zeros of the Riemann zeta function, for which he was awarded a Fields Medal in 1950, and for his "elementary" proof of the prime number theorem. His honors include the 1986 Wolf Prize in Mathematics.

Selberg was also involved in one of the most famous controversies regarding allocation of credit for a result. His controversy with Paul Erdös regarding the genesis of the "elementary" proof of the prime number theorem features in every account of Erdös' life and work. See, e.g., this book and this obituary.

Addendum: I just saw that Luca Trevisan also has a (better) post on Selberg's death. Luca points to an obituary on the IAS web pages.

LICS Test-of-Time Award 2007

The LICS Test-of-Time Award recognizes a small number of influential papers which appeared in the LICS proceedings from 20 years prior that have best met the “test of time”.

I have just read that the Awards Committee for 2007, consisting of Yuri Gurevich (Chair), Rajeev Alur, and Glynn Winskel, selected the papers

• Samson Abramsky, Domain Theory in Logical Form, and
  
• Robert Harper, Furio Honsell and Gordon Plotkin, A Framework for Defining Logics,
  

as winners of the 2007 LICS Test-of-Time Award (for papers from LICS 1987). Congratulations to the authors for this recognition of their work! For once, I could have successfully bet on those two papers winning the award for 2007 :-)

Programming the Universe

I recently finished reading the book Programming the Universe by Seth Lloyd, Professor of Mechanical Engineering at MIT. The book is a very pleasant, thought-provoking read, and its message is honey to the ears of us computer scientists. To see why, it suffices only to read the first few lines in Chapter 1 of the book.

This book is the story of the universe and the bit. The universe is the biggest thing there is and the bit is the smallest possible chunk of information. The universe is made of bits. Every molecule, atom, and elementary particle registers bits of information. Every interaction between those pieces of the universe processes that information by altering those bits. That is, the universe computes, and because the universe is governed by the laws of quantum mechanics, it computes in an intrinsically quantum-mechanical fashion; its bits are quantum bits. The history of the universe is, in effect, a huge and ongoing quantum computation. The universe is a quantum computer.

Basically, Seth Lloyd's message is that information is just as important as classic physical quantities like energy in understanding the universe, and that viewing the universe as a quantum computer can actually help us understand it better. He even proposes a theory of quantum gravity based on this view---a theory that, unlike others, may even be testable experimentally.

You might like to have a look at a scientist's cut from the material Lloyd penned down for the book here. There you will also find some interesting quotes from referee reports Lloyd received for some of his papers, and the following estimate on the number of operations performed by the universe since the big bang.

The universe can have performed 10¹²⁰ ops on 10⁹⁰ bits (10¹²⁰ bits including gravitational degrees of freedom).

I wonder if Scott Aaronson has reviewed this book on his blog. It would be interesting to hear his opinion.

Vardi on Process Equivalences

Last Saturday, Moshe Vardi posted the paper Branching vs. Linear Time: Semantical Perspective (invited ATVA'07 paper with Sumit Nain). This is a nicely written and balanced paper distilling Moshe's thoughts on the choice of semantics for concurrent processes. I have no doubt that it will generate some healthy discussion in the concurrency theory community. I strongly encourage my two readers to have a look at it.

Oversimplifying the message in the paper by Moshe and Sumit, in their opinion the plethora of process semantics is due to "semantic underspecification". To overcome this underspecification, they propose to develop process semantics based on the following principles.

1. Principle of Contextual Equivalence: Two processes are equivalent if they behave the
   same in all contexts, which are processes with “holes”.
2. Principle of Comprehensive Modeling: A process description should model all relevant
   aspects of process behaviour.
3. Principle of Observable I/O: The observable behaviour of a tested process is precisely
   its input/output behaviour.

In the paper, Moshe and Sumit apply their approach to transducers, and show that, once the aforementioned three principles are applied, there is a trace-based equivalence that is adequate and fully abstract.

As the authors state in the paper "In conclusion, this paper puts forward an, admittedly provocative, thesis, which is that process-equivalence theory allowed itself to wander in the “wilderness” for lack of accepted guiding principles. The obvious definition of contextual equivalence was not scrupulously adhered to, and the underspecificity of the formalisms proposed led to too many interpretations of equivalence.While one may not realistic expect a single paper to overwrite about 30 years of research, a more modest hope would be for a renewed discussion on the basic principles of process-equivalence theory."

What do you think?

Rivest Wins Marconi Prize

MIT's Department of Electrical Engineering and Computer Science continues its rich harvest of awards. My RSS feeds monitor has informed me that Ron Rivest has been awarded the Marconi prize. See here for the MIT news item. Rivest has been named the 2007 Marconi Fellow and prize-winner for his pioneering work in the field of cryptography, computer and network security.

The Parking Algorithm

Furio Honsell is one of Italy's best known theoretical computer scientists. His research covers many areas within volume B TCS, and he was one of the proposers of the ‘Anti-Foundation Axiom’ for non-well-founded set theory. Furio was the first computer scientist to become rector of an Italian university, Università di Udine to be precise, and is now serving his second mandate as rector.

Unlike most of us, Furio is also known to the general Italian public for his participation in the TV show Che tempo che fa, where he discusses topics related to computer science and mathematics in a way that makes them accessible to a general audience. My mother, for instance, is fascinated by his witty and very clear discussions of topics that normally would not be aired on a TV show.

What has this all to do with "The Parking Algorithm"? A few days ago, walking back to my deck chair after a swim in the Adriatic sea, I saw a man read a volume by Furio entitled "L'Algoritmo del Parcheggio" ("The Parking Algorithm"), published by Mondadori, which is a major Italian publishing house. I was amazed. I stopped and asked this man whether I could write down the bibliographic details for the book, which I simply had to buy!

Furio is definitely doing a lot for promoting an appreciation for computer science and mathematics amongst the general educated public in Italy, and he must be doing it right if people read his book on the beach! I know that this is one of my, possibly boring, mantras, but we badly need more people who, like him, are not afraid to devote some of their time to writing books and articles for the general public, and who have the charisma to appear on TV and captivate viewers like my mother or that man who ended up buying his book and reading it under the sun-shade. (I also admire his time-management skills. Being a rector does not leave him a lot of time for research or book writing.)

For the record, I did buy Furio's book, but I'll have to wait for my mother to finish reading it before having a close look at it. I'll review Furio's book at some point in the future, but don't hold your breath.

"Reactive Systems" Is Out: Buy Your Copy Now!

A few days ago, I checked the web page at Amazon.co.uk for my latest book Reactive Systems: Modelling, Specification and Verification, which I have already shamelessly advertised in previous postings. I was surprised to read that only four copies were left in stock (and only one is in stock right now, so hurry!), especially because the official publication date for the book is 9 August 2007.

My copy of the book landed in my mailbox yesterday, as partial compensation for the departure of the hard disk in my laptop, the only computer I own :-( It was quite an experience to browse through the results of a few years of work while wondering whether I really had any part in writing the text filling those pages. This is how I often feel whenever I look at some work of mine. Was it really I who contributed to write/do that work? Something to ponder while waiting for a new hard disk, even though I know that it was really a different person from the one typing these characters who did it.

Anyway, I hope some of you will like the book, whoever wrote it.