Papers I find interesting---mostly, but not solely, in Process Algebra---, and some fun stuff in Mathematics and Computer Science at large and on general issues related to research, teaching and academic life.
Tuesday, June 19, 2007
Avi Wigderson's Louis Clark Vanuxem Lectures
The plan for Wigderson's series of lectures is as follows.
There is a lot of inspiration to be drawn from those slides. Is TCS really the "new math"? Only time will tell, but this really a good refrain to listen to anyway :-)
Friday, June 15, 2007
Computing Community Consortium Workshop at FCRC
This week the CCC is organizing a workshop at the 2007 Federated Computing Research Conference. The slides for the contributed talks given so far are available here. (Lazowska's slides are still missing at the time of writing since his talk will be delivered today. I am looking forward to seeing them!) They are all interesting at first sight. In particular, I want to encourage readers of this blog to look at the wonderful slides for Christos Papadimitriou's talk on the Algorithmic Lens. The slides give Christos Papadimitriou's view of the impact that computer science is having on other sciences, and can offer all of us plenty of food for thought as well as material for enticing students to CS.
In case you do not have time to look at the slides, the executive summary of the talk, presented on the last slide reads:
- The algorithmic world view is changing the sciences: mathematical, natural, life, social
- CS is placing itself at the center of the scientific discourse and exchange of ideas
- And this is only the beginning…
Addendum: Ed Lazowska's slides are now on line.
Monday, June 11, 2007
Rejecting Excellent Papers
A recent, remarkable instance of this kind of rejection is mentioned in a letter in the latest issue of the Notices of the AMS. (See here, on page 2 of the file. The letter is co-signed by Vaughan Pratt, one of my favourite theoretical computer scientists.) Apparently, the editorial board of the Journal of the AMS, which is the flagship journal of the American Math Society, has declined to publish a 14-page paper reporting on Friedrich Wehrung's solution to Dilworth's Congruence Lattice Problem for its lack of “interaction with other areas of mathematics”. The problem had been open for about fifty years, and drove the development of lattice theory during that time. See this web page for more information.
I am sure that the author will rapidly publish the paper in a top-notch journal, given that it had glowing referee reports. What I am not sure of is how many, apparently superb papers, a journal can decline to publish before authors stop submitting to it.
I guess that, as usual, the great judge will be Time.
Addendum 12 June 2007: A look at Friedrich Wehrung's publications page indicates that the aforementioned paper of his is going to appear in Advances in Mathematics.
Friday, June 08, 2007
June/July Notices of the AMS
Enjoy.
Thursday, June 07, 2007
Invited Speakers at ICALP 2008
- Ran Canetti (IBM T.J. Watson Research Center and MIT, USA),
- Bruno Courcelle (Labri, Universitè Bordeaux, France),
- Javier Esparza (Technische Universität München, Germany),
- Muthu Muthukrishnan (Google, USA) and
- Peter Winkler (Dartmouth, USA).
Anna, Magnus and I are very glad to be able to offer participants at ICALP 2008 this outstanding set of invited talks.
Preliminary call for workshops and call for papers will be posted on this blog and on mailing lists very soon. Watch this space if you want to be the first to know!
Tuesday, June 05, 2007
AITO Dahl-Nygaard Prize Winners for 2007
I am very pleased to see Luca Cardelli honoured in this way, and I trust that this won't be the last award he will receive for his outstanding research achievements. Luca is a one-man research team, and he is equally at ease in theoretical as well as in implementation work. The text accompanying the notification singles out his famous book "A Theory of Objects", published with Martin Abadi in 1996, the Ambient Calculus (developed with Andy Gordon) and his work in Computational Systems Biology.
Congratulations to Luca!
Ranking
I have not played with the authors' system yet, but the tables they present to substantiate its quality make for some interesting reading. The top five computer science departments in the US, according to their ranking, are as follows.
- MIT
- University of Maryland, College Park
- CMU
- Georgia Institute of Technology
- Stanford
In Software Engineering, as an Italian abroad I am glad to see the Politecnico di Milano in 8th place and the University of Bologna in 41st. Amongst individual researchers in SE, Paola Inverardi is ranked 17th. Perhaps interestingly, the SE rankings given in the article differ significantly from those obtained by others in a previous ranking exercise.
This is what the authors have to say.
Our ranking is significantly different from the JSS ranking. The second column in Table 2 shows that only two of the top 15 institutions from the JSS ranking are among the top 15 of our ranking. The second column in Table 3 shows that only two of the top 15 scholars from the JSS ranking are among the top 15 of our ranking.Two policy disparities probably contribute to the difference. First, we included two conferences in our ranking that the JSS ranking did not consider. Secondly, our ranking and the JSS ranking selected different journals and these journals contributed scores differently. The JSS ranking heavily relies on papers published in itself and the journal Information and Software Technology. It also includes a magazine, IEEE Software. The JSS ranking receives almost no influence from ACM Transactions on Software Engineering and Methodology. This study illustrates that the framework can produce dramatically different results when used with different policies, even for the same field.
What does this indicate? Automatic rankings will be very useful in the future, but it will be all the more important to specify clearly how such rankings are obtained. In particular, when evaluating the results of such ranking exercises, I'd really like to know what publication outlets were considered, what weight they were given, and what weight was given to multi-authored papers. I do not see why the author of a multi-authored paper should necessarily receive a fraction of the points awarded to the paper. Is writing a paper with a co-author less work than doing it alone?
Monday, June 04, 2007
Invited Paper for CONCUR 2007
I have posted my contribution to the Proceedings of CONCUR 2007. The paper, coauthored with Anna and entitled The Saga of the Axiomatization of Parallel Composition, is a survey of recent work Anna and I have done in collaboration with Wan Fokkink, Bas Luttik and MohammadReza Mousavi. We published some of this work directly in journals, and so it felt appropriate to present it in a conference proceedings. I'll be basing my invited talk at CONCUR on the paper.
Thanks a lot to Anna, Bas, Mohammad and Wan for our pleasant collaborations so far. I hope to do some justice to our joint work in Lisbon. It'll be a bit of a challenge to make the audience interested in the story I have to tell, but it is one I hope to meet decently well. It'll be up to the participants at CONCUR 2007 to tell whether I'll succeed.
Surprisingly, the list of accepted papers for the conference is not yet available from the CONCUR 2007 web site. I am looking forward to viewing the programme for this event.
Thursday, May 31, 2007
The Value of a PhD
As will be clear to those of you who read that piece, the "unapologetic mathematician" can write! For what it is worth, I agree with what he says. Here is an excerpt I really liked.
Amen. In a society where money is the only thing that seems to matter, and where any line of study carrying one or more of the tags "business", "financial" or "media" attracts hundreds of students, it is good to see somebody sing the praises of adding a little to the honour of the human spirit.
The doctorate is the gold standard of the academy. You can’t get it by spitting back answers on a sequence of course finals. You can’t get it by retaining the material until a collection of comprehensive exams, or by writing up a survey of relevant literature. You attain a doctorate by extending the boundaries human knowledge.This society generally speaks well of originality, but it tends to mean a rather pale sort. To really, truly think of something nobody else has before — and to be able to justify it — is really far more difficult than most people give credit to. It’s not something you do on weekends, in your spare time while doing other more important things. The Great Work is hard. It means steeping yourself in a subject until you understand in a way only a handful of other people do. It means sacrificing years of your life to the pursuit of something truly new and different. The path is littered with those who started and did not make it through to the end.
And it has no justification but itself. Nobody goes into academics for the money. Nobody does it for the praise of the masses. Compared to most other things any of these new doctors could have done it will be temporally thankless. You live the academic life because you look outside at the amazing world around yourself and you realize that, for you, the highest achievement of the human spirit is to understand it more deeply — to internalize some aspect of it, digest it, and help share that with the rest of humanity. You do it because it is fundamentally worth doing. The life of the mind has a value in and of itself. And so these men and women have chosen this value over all the others they might have.
Tuesday, May 29, 2007
A Journal Without Editors
"For information regarding current submissions please contact topology@elsevier.com. "As you probably know, the entire editorial board of Topology resigned last year. (The resignation letter is available here.) The board has founded a new journal, Journal of Topology, published by the London Mathematical Society and Oxford University Press. The price of the journal will be roughly one third of the price of the Elsevier journal.
Saturday, May 26, 2007
Second ICE-TCS Annual Report
ICE-TCS operates on a shoestring budget, but we hope that the local funding agencies will become interested in investing in "centres of excellence" and that they'll consider ICE-TCS to be one of those. (Fat chance :-)) In the unlikely event that this happens, I'll announce available visiting positions on this blog. Watch this space.
Wednesday, May 23, 2007
The Wrecking of British Science
Why am I droning on about this guy, you may ask? The reason is that I just read this article he wrote for the Guardian. (I strongly recommend that you read it, especially if your heart still feels for the British university system like mine does.) The picture Kroto paints is bleak, but all too familiar, alas. Throughout the western world, the number of students interested in science is declining frighteningly, at a time when our society is so dependent on science. As Kroto writes in that article:
Scientific education is by far the best training for all walks of life, because it teaches us how to assess situations critically and react accordingly. It gives us an understanding based on reverence for life-enhancing technologies as well as for life itself. If we do not know how things work, how can we fix things? And how are we going to use these powerful technologies wisely?Even more important than the training for non-existent jobs is the worrying decrease in our society of that willingness to think critically, to work on problems, to be creative, and to challenge ourselves that are one of the main ingredients of our humanity. I sincerely hope that the new Icelandic government that was formed today will work proactively to put science on the agenda in Icelandic schools at all levels. It is a small step, but one has to start somewhere.The situation in universities is exacerbated by present policy, which actively encourages vice-chancellors who know the cost of everything and the value of nothing to eliminate science departments in favour of trendy, cheap courses. These VCs bleat about how important their freedom is to do whatever they wish with taxpayers' money, and steer funds earmarked for the sciences into softer areas that students prefer.
Just as cheap fast food has resulted in unprecedented levels of obesity, so this McDonald's approach to cheap, trendy, seductively soft courses designed for mass consumption in tertiary education has resulted in a plethora of students trained for non-existent jobs.
Sunday, May 20, 2007
Elsevier's Computer Science Review
Wolfgang Thomas recently pointed out to me a new Elsevier journal by the name of Computer Science Review. The aim of this journal is to publish research surveys and expository overviews in computer science and related fields. The reviews are aimed at a general computer science audience.
I was not aware of this new Elsevier journal, and my feeling is that its aim overlaps somewhat with that of the columns in the Bulletin of the EATCS. As one of the column editors, so far I have been extremely impressed by the willingness of the members of the concurrency theory community to contribute to the Bulletin. However, when I read at http://www.elsevier.com/wps
"Submissions are free of charge and recognizing the work involved in preparing a review article, Elsevier will pay authors for their contributions to Computer Science Review. This amount will be Euro 400 per accepted article for the authors; provided the article meets minimum length requirements (at least 20 typeset pages, preferably more). Book reviewers will be paid for comprehensive book review contributions - EUR 15 per typeset page, to a maximum of EUR 100." (The emphasis is mine.)
I cannot help but being worried about the future of the columns. Paying authors for their contributions to a journal is a remarkable development, and can even be seen as unfair competition :-) Sure, we are not talking about large sums of money, but I am not aware myself of any other journal in computer science that pays its contributors. Do you know of any journal that does so?
I wonder whether this move by Elsevier heralds a new era in which commercial publishers will reward authors, editors and referees financially. I am not sure that this would be a positive development myself. (Only once so far I have been "paid" for a journal review, and was very surprised when the cognizant editor offered to pay me. I received a 50-euro book voucher for reviewing a paper that had been awaiting a referee report for about three years and that, for some reason that I cannot understand yet, nobody wanted to evaluate.)
As Moshe Vardi often says, our currency is reputation, not money. Call me an idealist, but I'd like to keep things this way.
Comments on the issue of payment for journal papers, review articles and book reviews are most welcome. I'd really love to hear what you think about this new development.
Friday, May 18, 2007
Concurrency Column for the June 2007 Issue of the BEATCS
In this piece, Orna Kupferman, who is one of the prime movers in the study of automata-theoretic constructions and in their application to the verification of reactive systems, presents a survey of several automata-theoretic problems in which the gap between the known upper and lower complexity bounds is exponential, and describes recent efforts to close the gaps.
I am glad to be able to offer this piece to the readership of the concurrency column and of this blog, and I trust that you will enjoy reading it as much as I did.
Monday, May 14, 2007
PCs for ICALP 2008
ICALP 2008 will have three tracks, and the PCs for the three tracks have been formed. They are as follows.
Track A
- Michael Bender (State Univ of New York at Stony Brook, USA)
- Magnus Bordewich (Durham University, UK)
- Peter Bro Miltersen (Aarhus University, Denmark)
- Lenore Cowen (Tufts University, USA)
- Pierluigi Crescenzi (Università di Firenze, Italy)
- Artur Czumaj (University of Warwick, UK)
- Edith Elkind (University of Southampton, UK)
- David Eppstein (University of California at Irvine, USA)
- Leslie Ann Goldberg (University of Liverpool, UK) (chair)
- Martin Grohe (Humboldt-Universität zu Berlin, Germany)
- Giuseppe Italiano (Università di Roma "Tor Vergata", Italy)
- Christos Kaklamanis (University of Patras, Greece)
- Michael Mitzenmacher (Harvard University, USA)
- Ian Munro (University of Waterloo, Canada)
- Ryan O'Donnell (Carnegie Mellon University, USA)
- Dana Ron (Tel-Aviv University, Israel)
- Tim Roughgarden (Stanford University, US)
- Christian Scheideler (Technische Universität München, Germany)
- Christian Sohler (University of Paderborn, Germany)
- Luca Trevisan (University of California at Berkeley, USA)
- Berthold Vocking (RWTH Aachen University, Germany)
- Gerhard Woeginger (Eindhoven University of Technology, the Netherlands)
Track B
- Parosh Abdulla (Uppsala University, Sweden)
- Luca de Alfaro (University of California, Santa Cruz, USA
- Christel Baier (Technische Universität Dresden, Germany)
- Giuseppe Castagna (Université Paris 7, France)
- Rocco de Nicola (Università di Firenze, Italy)
- Javier Esparza (Technische Universität München, Germany)
- Marcelo Fiore (University of Cambridge, UK)
- Erich Grädel (RWTH Aachen, Germany)
- Jason Hickey (California Institute of Technology, USA)
- Martin Hofmann (Ludwig-Maximilians-Universität München, Germany)
- Hendrik Jan Hoogeboom (Leiden University, NL)
- Radha Jagadeesen (DePaul University, USA)
- Madhavan Mukund (Chennai Mathematical Institute, India)
- Luke Ong (Oxford University, UK)
- Dave Schmidt (Kansas State University, USA)
- Philippe Schnoebelen (ENS Cachan, France)
- Igor Walukiewicz (Labri, Universitè Bordeaux, France) (chair)
- Mihalis Yannakakis (Columbia University, USA)
- Wieslaw Zielonka (Université Paris 7, France)
Track C
- Christian Cachin (IBM Research Zurich, CH)
- Jan Camenisch (IBM Research Zurich, CH)
- Ivan Damgård (Aarhus University, Denmark) (chair)
- Stefan Dziembowski ((Università di Roma "La Sapienza", Italy)
- Dennis Hofheinz (CWI Amsterdam, the Netherlands)
- Susan Hohenberger (Johns Hopkins University, USA)
- Yuval Ishai (Technion Haifa, Israel)
- Lars Knudsen (DTU Copenhagen, Denmark)
- Arjen Lenstra (EPFL Lausanne, CH)
- Anna Lysyanskaya (Brown University, USA)
- Rafael Pass (Cornell University, USA)
- David Pointcheval (ENS Paris, France)
- Dominique Unruh (Saarland University, Germany)
- Serge Vaudenay (EPFL Lausanne, CH)
- Bogdan Warinschi (Bristol University, UK)
- Douglas Wikström
- Stefan Wolf (ETH Zurich, CH)
For the moment, plan to submit your best papers to ICALP 2008 and use this chance to make a visit to Iceland and to our ICE-TCS research centre!
Sunday, May 13, 2007
The End of an Era
A byproduct of Jaco's move to Twente is that the process algebra group at CWI, which over the years has been headed by Jos Baeten, Frits Vaandrager, Jan Friso Groote, Wan Fokkink, and finally Jaco van de Pol, will be terminated. It is a fact of life that all (good) things must eventually come to an end, but I cannot help but feel that this is truly the end of an era.
The work of the process algebra group at CWI has played a major role in my scientific development, and I have had the pleasure to collaborate on various projects with several of its leaders mentioned above. (Disclaimer: The process algebra group at CWI is not responsible for the outcome of my work :-)) I like to think that the legacy of that group will be felt for many years to come. Indeed, one of the signs of its impact on Dutch computer science is the fact that all of its leaders over the years are now professors and leaders of strong research groups in some of the best Dutch universities.
Even though my work owes a lot to the intellectual inspiration of the process algebra group at CWI, I only visited CWI once in September 2005, and then only for a day to deliver a talk in the well-known PAM series---well, well-known amongst process algebraists. I guess that this indicates how little I travel around, and that one can be influenced by the work carried out at an institution without having ever visited it. (As another example, I owe a great debt to the Edinburgh concurrency school, but I have never visited Edinburgh.)
I vividly recall that, while introducing my talk at CWI, I paraphrased a famous sentence by the Italian writer Alessandro Manzoni and said that I felt that I had finally gone to Amsterdam to wash my process algebra clothes in the Amstel. With the demise of the process algebra group at CWI, it will unfortunately become a lot harder to wash my process algebra clothes in the Amstel.
Friday, May 11, 2007
What is Time?
In order to achieve a higher degree of generality, in the technical report
A. Jeffrey, S. Schneider, and F.W. Vaandrager. A comparison of additivity axioms in timed transition systems. Report CS-R9366, CWI, Amsterdam, 1993
the authors proposed to consider an algebraic definition of time domain. Since I like that definition, and I have it used it myself in a couple of papers, allow me to use this post to publicize it.
Define a monoid (X,+, 0) to be:
- left-cancellative iff (x + y = x + z) implies (y = z), and
- anti-symmetric iff (x + y = 0) implies (x = y = 0).
All of the structures mentioned above are, of course, time domains, but so is the set {0}. A time domain is non-trivial if D contains at least two elements. Note that every non-trivial time domain does not have a largest element, and is therefore infinite. Note moreover that + is not required to be commutative, so, for instance, suitable sets of ordinals with ordinal addition form a time domain.
I often find it worthwhile to work with time domains specified with the above degree of generality, and to use properties of specific "concrete" time domains only when they are really needed to obtain certain results. However, maybe this is the axiomatic devil in me talking :-)
Why hasn't the above definition become more popular in the literature on timed process algebras?
Tuesday, May 08, 2007
Gödel Prize 2007
The Gödel prize 2007, co-sponsored by EATCS and ACM SIGACT, is awarded to Alexander A. Razborov and Steven Rudich for their paper "Natural Proofs", Journal of Computer and System Sciences, Vol. 55, No. 1, 1997, pp. 24-35. (The conference version of the paper was first presented at the Twenty-sixth Annual ACM Symposium on Theory of computing, Montreal, Quebec, Canada. 1994, pp. 204 - 213.)
For discussions of the importance of this result in computational complexity, see here, and here. (Two posts from two of my favourite blogs.) Wikipedia has an entry on natural proofs.
Congratulations to Alexander A. Razborov and Steven Rudich, two outstanding members of the TCS community, for the award.
Addendum: The citation for the award is available here.
Friday, May 04, 2007
Iceland as an International Workplace in Science
Today, I participated in the workshop "Ísland sem alþjóðlegur vinnumarkaður vísindanna" ("Iceland as an international workplace in science") organized by Rannis, the Icelandic fund for research. At the workshop I delivered a presentation entitled How Do you Like Iceland? A View from a Foreign Academic. In case anybody is interested, the slides for my talk are available here. As you can see, I tried to give the Icelandic attendees a cathartic experience and some food for thought.
The latter part of this interesting workshop was attended by a few politicians. I am happy to report that all of them went on record as saying that the amount of funding available for science in Iceland should be increased substantially. Hopefully, these words will turn into deeds after the elections 
Thursday, May 03, 2007
Robert H. Sloan on Being an NSF Program Director
Here is a quote I liked:
Being a program director also gives you the ability to provide two good services to your research community. First, you have some ability to drive the direction of the research community. Second, you get to run the best, fairest competitions for funding possible. There is really quite a difference between the best panel run by somebody who knows the research area, knows who are likely to be good panelists, and is good at managing such things, and a panel run by an outsider who is a fair to middling manager of such things.
Indeed there is, but somehow we all hope that it is somebody else who takes care of running the best and fairest for funding possible.
The Geomblog offers another quote from the piece on the hazardous job of being Dean of Undergraduate Studies.
On the topic of community service, my stint as head of department is going to end in a couple of weeks or so. My department and the School of Science and Engineering have undergone a sudden restructuring, and we have hired Ari K. Jónsson (NASA Ames) to become Dean of the new School of Computer Science. I'll write more on all of the above when the dust settles, and I find some breathing space.
Sunday, April 22, 2007
Accepted Papers for CALCO 2007
Meanwhile, the by now fairly typical discussion on the role of FOCS/STOC in TCS is raging on the complexity weblog. You will probably enjoy reading it. As usual, I find the idea that STOC and FOCS represent all theoretical computer science difficult to defend. Mind you, FOCS and STOC are great conferences, but many areas of TCS are not represented in recent editions of those conferences.
When did volume B research stopped being represented at those conferences? When I have a little time on my hands, I might try to investigate this question. I'd appreciate hearing the opinion of whoever is out there.
Thursday, April 19, 2007
Paul Graham's Take on Judgements
A second much more common type of judgement does not have the goal of judging you correctly. As Graham writes:
It's not aimed at producing a correct estimate of any given individual, but at selecting a reasonably optimal set.
We meet this type of judgement whenever we submit a paper to a conference or workshop. Of course, we all feel that our work is worthy of selection when we submit it. (Indeed, as they say in Naples, "Even a cockroach is beautiful for its mum".) That is why we are usually not so good at accepting that our papers are not selected for presentation at an event. Here Graham's following words from his essay may be worth keeping in mind:
Our early training and our self-centeredness combine to make us believe that every judgement of us is about us. In fact most aren't. This is a rare case where being less self-centered will make people more confident. Once you realize how little most people judging you care about judging you accurately—once you realize that because of the normal distribution of most applicant pools, it matters least to judge accurately in precisely the cases where judgement has the most effect—you won't take rejection so personally.
And curiously enough, taking rejection less personally may help you to get rejected less often. If you think someone judging you will work hard to judge you correctly, you can afford to be passive. But the more you realize that most judgements are greatly influenced by random, extraneous factors—that most people judging you are more like a fickle novel buyer than a wise and perceptive magistrate—the more you realize you can do things to influence the outcome.
Indeed, we could all try to write better papers that sell our ideas---once we have them, that is. As Paul Halmos famously wrote in his automathography:
"I love to do research, I want to do research, I have to do research, and I hate to sit down and begin to do research---I always try to put it off just as long as I can. ....Isn't there something I can (must?) do first? Shouldn't I sharpen my pencils perhaps?"
Anyway, Paul Graham's essays are well worth reading while sharpening one's pencils. (Have you heard the scraping sound of my pencil sharpener for some time now?) Check out also his recent essay on the death of Microsoft. You might also enjoy looking at the web page for his new venture firm, Y combinator. Cool name, isn't it?
Friday, April 13, 2007
Mathematicians Map E8
This is by now old news, but I liked reading this report on the work that mathematicians in the Atlas project did to map the inner workings of one of the most complicated structures ever studied: the object known as the exceptional Lie group E8. Reading sentences like:
"The most important thing that we've done is written an algorithm which converts some very difficult abstract mathematics, the representation theory of real groups, into combinatorics which can be computed. This is a substantial accomplishment."
and
"In the process of taking these known mathematical results, and converting them into a computer program, we have deepened our understanding of the mathematics."
should be like honey to the ears of us computer scientists.
E8 in the news gives pointers to news coverage on the work that the people in the Atlas project did.
It is now time to join the discussion with our evaluation committee.
Monday, April 09, 2007
Nancy Lynch is Awarded Knuth Prize
The award of the Knuth Prize to Nancy is a great advertisement for the areas of distributed computing, and modelling, verification and validation of computing systems. Congratulations to Nancy! I look forward to seeing more awards to outstanding women in computer science.
Friday, March 16, 2007
Computing Degrees and Careers Information from the ACM
opportunities. Of note is also the information on the web site, including Frequently Asked Questions and Top 10 Reasons to Major in Computing.
I will be using this material in my efforts to attract Icelandic students to computer science. I must freely admit that, with all due respect to civil engineering, I find it very difficult to understand why students choose that field of studies in large numbers, and do not even consider computer science. As my Latin ancestors would have said, "De gustibus non disputandum est" ("There is no arguing about tastes").
Thursday, March 15, 2007
Concurrency on Ars Mathematica
It is good to see mathematicians referring to concurrency theory, even if just on their blogs and for a quote from André Weil :-)
Wednesday, March 14, 2007
Enticing Students to Learn CS
Based on these (for us obvious) premises, one would expect student enrollments in our CS degrees to be increasingly high. Unfortunately, as of today, the figures paint a totally different, and utterly inexplicable and depressing, story. The number of applications is at an all-time low, and we are considering many plans to try and stop the rot. At the same time, enrollment in several engineering degrees is increasing. Even female students are now considering engineering as a viable subject to study. Instead, CS does not seem to cross their mind at all.
Could this have to do with the totally wrong equation "computer science = programming"? And what about the stereotype that a computer scientist is an autistic, male, sun-avoiding, coke-drinking nerd who programs and fixes computers all day? I have no answers to these questions. These days I am putting on my travelling salesman clothes, and give (hopefully energetic) talks on the beauty and importance of CS to a few high-school students who bother to show up. Whether this will have any effect I do not know. What I do believe is that it is time to send out the powerful message that computer science is the science of the 21st century Renaissance man. No other science today touches on so many others, and on society as well. What we need are more people like David Harel and Jeannette Wing who have the courage to explain CS and its basic ideas to the rest of society, including our fellow scientists---many of whom just consider computing as a useful technology.
Let's pick up the gauntlet, and put pen to paper.
Friday, March 09, 2007
Some Results on BPA with Interrupt
In the present paper we show that, unlike bisimilarity, complete trace equivalence affords a finite, ground-complete axiomatization, provided that the set of actions is finite. Moreover, we show that, when the set of actions is a singleton, the interrupt operator is a derived BPA-operator, and that complete trace equivalence affords a finite complete axiomatization over BPA with interrupt.
In the presence of at least two distinct actions, we isolate a collection of valid equations. A proof of their (in)completeness has so far escaped us. Feel free to get in touch with me if you have any idea on how to prove this!
Saturday, March 03, 2007
The Equational Theory of Timed CCS
The aim of the paper is to revisit the study of the equational theory of parallel composition in TCCS by obtaining results in the spirit of those that Faron Moller showed for Milner's CCS. We prove that timed bisimilarity is not finitely based over TCCS. Moreover, unlike in the setting of CCS, adding two "natural" variations on the (timed) left-merge operator to TCCS does not yield a finitely axiomatizable theory.
In passing, we sharpen the so-called Gap Theorem of J.-C. Godskesen and Kim G. Larsen by showing that it holds also in the setting when the set of actions is a singleton. Unlike the proof of the original result by those authors, which goes via a translation to timed automata, ours is entirely process algebraic.
Thanks to Anna and Mohammad for a pleasant, instructive and humbling collaboration. I, for one, am always overawed by the fragility of these results. One has to be very careful in making sure that the technical details work. An apparently innocuous change in the semantics of the operators can make a huge difference in their properties, and thus in the validity of the statements one is trying to prove. Our ICE-TCS seminar speaker yesterday, Freyja Hreinsdóttir, quoted a mathematician as referring to a conjecture as being "obviously true, but unproven". I am afraid that I do not trust those statements. For what it is worth, my "obviously true, but unproven" conjectures turn out to be false more often than not :-(.
Thursday, March 01, 2007
Ready to Preorder
In the paper we offer an algorithm for turning an axiomatization for a behavioural preorder in the linear time-branching time spectrum that includes the ready simulation preorder into an axiomatization for the kernel of the preorder. The algorithm preserves finiteness, ground-completeness and omega-completeness of the axiomatization that it receives as input. The proof of its correctness relies on an analysis of the so-called cover equations for the semantics in the spectrum we study in the paper.
I thoroughly enjoyed working on that paper. The development of the technical details in that work reminded me yet again of a few valuable lessons that I tend to forget when I feel that I am short of time and that I badly need to produce some research output to keep my conscience at bay.
- It is easy to make mistakes in proofs unless one is very careful in checking even the seemingly most obvious of claims. (This is what happens to me at least.)
- Haste is never a good advisor.
- When I feel that a paper is done, I should let it rest for a day, and proof read it once more.
Thanks again to Anna and Wan, the coauthors with whom I have written the largest number of papers, for another very instructive and pleasant collaborations. I hope that there will be another one in the near future.
Friday, February 23, 2007
Tom Henzinger Named ACM Fellow 2006
What might be less known, however, is that Tom Henzinger was named amongst the ACM Fellows for 2006. Tom is selected for contributions to formal verification and hybrid systems. Tom's ACM fellowship is very good for the fields of computer-aided verification, concurrency theory and TCS at large.
Congratulations Tom!
Wednesday, February 21, 2007
Two Posts on Martin Kruskal
By the way, Joseph Kruskal of minimun spanning tree fame is Martin Kruskal's brother. (Historically, the first algorithm for finding a minimum spanning tree was developed by Czech scientist Otakar Borůvka (see Boruvka's algorithm).)
Saturday, February 17, 2007
Tao on "Good Mathematics"
The final lines of the piece will serve as an appetizer.
Thus I believe that good mathematics is more than simply the process of solving problems, building theories, and making arguments shorter, stronger, clearer, more elegant, or more rigorous, though these are of course all admirable goals; while achieving all of these tasks (and debating which ones should have higher priority within any given field), we should also be aware of any possible larger context that one’s results could be placed in, as this may well lead to the greatest long-term benefit for the result, for the field, and for mathematics as a whole.
Well said indeed!
Wednesday, February 14, 2007
EATCS Award 2007
Dana Scott has also received the following prizes:
| LeRoy P. Steele Prize | American Mathematical Society, 1972 |
| Turing Award (with Michael Rabin) | Association for Computing Machinery, 1976 |
| Harold Pender Award | University of Pennsylvania, 1990 |
| Rolf Schock Prize in Logic and Philosophy | Royal Swedish Academy of Sciences, 1997 |
| Bolzano Medal for Merit in the Mathematical Sciences | Czech Academy of Sciences, 2001 |
See here for some biographical information.
EATCS AWARD 2007
MOTIVATION
Dana Scott is an outstanding scientist with a deep and lasting influence on Theoretical Computer Science. In a few words his contributions belong to three tracks of fundamental research:
- The introduction, in collaboration with Rabin, of non-deterministic machines in Automata Theory, which earned them the 1976 ACM Turing Award.
- The mathematical foundation to the denotational semantics of programming languages, also known as the Scott-Strachey approach to semantics, for which he is best known in Theoretical Computer Science.
- The invention of LCF (Logic for Computable Functions), which was hugely influential in the development of program logics and modern proof checking technology.
More recently he has further advanced the foundations of denotational semantics in two directions: Synthetic Domain Theory (a way to view domains as sets in a non-standard set theory) and Equilogical Spaces, which appear to be a natural extension of domains.
In 1930-40 the work of mathematicians such as Goedel, Turing, Tarski, and Church had profound consequences on Mathematical Logic and gave origin to Computability Theory. Dana Scott is among the top researchers who carried that mathematical tradition into Computer Science. Denotational semantics is the natural evolution of Tarskian (compositional) semantics for logical languages into the realm of programming languages, and Domain Theory provides the needed semantic objects. In particular, effectively-given domains (and Information Systems) extend the notion of computability well beyond natural numbers and strings.
LCF was a major contribution to program logics, which led to work on PCF, sequentiality, higher-type computability, and modern proof checking technology.
Dana Scott has obtained fundamental results also in Set Theory, Model Theory, Modal Logic, Topology, Category Theory, and Realizability. His work on constructive mathematics, and also his lucid expositions of the work of others, had a great influence on the uses non-classical logics (e.g. constructive reasoning, modal logics for concurrency, propositions-as-types) in computing. He made a whole generation see the potential of non-standard logics, an idea as revolutionary as the one of non-standard geometries had been.
Dana Scott's research career has spanned Computer Science, Mathematics, Logic, and Philosophy, and has been characterized by a concern for elucidating fundamental concepts, with a focus on mathematically hard problems that bear on these concepts. His influence in forming
mathematical foundations for Computer Science is now visible over a period of over 40 years. The European research community of Theoretical Computer Science owes a lot to his thoughts and is flourishing while pursuing the directions he started.
Tuesday, February 13, 2007
Brain Drain and Brain Gain, Redux
I've read your recent post with interest, as I make part of the minority that has chosen Italy as a place to do a PhD. I am a Colombian, and have recently joined the CS department at Bologna,
under a new scheme for admitting (and reserving scholarships) for foreigner students.
Two specific comments on the post:
- It is certainly surprising to observe that Italy and Colombia share this "runaway brains" problem. This, of course, occurs because of very different reasons. Naturally, the surprise behind all this is that Italy is a G8 country and Colombia is a third-world country that spends most of its money on military expenses.
- Recently, there has been an increasing offer of PhD positions in CS for foreigners. Indeed, a number of CS departments (e.g., Bologna, Pisa, Verona, Trento) now admit foreign applications, usually based on CV and recommendation letters. This seems to be the right direction in order to compete with other European countries. Moreover, this initiative could be imitated in several other fields.
I have to say that even with the problems Italy has in some aspects of doing research, at Colombia Italy is seen as a very attractive option to do a PhD in CS. The possibility of working with strong researchers is an incredible advantage that, in several ways, compensates some
things that could be considered as drawbacks.
Sunday, February 11, 2007
Brain Drain and Brain Gain
I do not have that much to add to Luca T.'s analysis, so I'll just limit myself to adding a couple of comments, and to reiterating some opinions and facts that I already stated in some related posts.
First, let me go on record once more as stating clearly that there is a lot of talent in Italian universities. Italian researchers perform very well despite the lack of support the system gives them. However, Italy must do its very best to attract outstanding, foreign scientists (and students) in order to compensate for its brain drain. (I hate this expression, but it has become so widely used that I am forced to use it too.) This won't happen unless much needed, expensive, and probably very unpopular structural changes are made.
Every CS department in virtually every university that matters in the world has foreign members of staff and foreign students (at least at MSc and PhD level). A look at an average Italian department paints a different picture. According to the interesting little book Ipotesi sull'università by the mathematicians Mariano Giaquinta and Angelo Guerraggio only 2% of the students in Italian universities are foreigners. Moreover, for good or for worse, an observer is not unlikely to notice a certain amount of academic inbreeding in the lineage of members of staff.
Something is badly wrong when a school of the outstanding quality of the Scuola Normale Superiore di Pisa has 11 PhD scholarships in mathematics, receives only 13 applications (all from Italian candidates, and none from the school itself), and selects only 4. (Source: Una storia inquietante (An unresting story) by Mariano Giaquinta and Angelo Guerraggio in Lettera Matematica Pristem 60, pp. 4-6.) Does this mean that even a school of that quality does not advertise its vacancies internationally? Or, possibly even worse, does this mean that no student out there perceives that school in Italy as a good location for PhD education? The lack of local applicants might be read as indicating that Italian students with an MSc in mathematics from the Scuola Normale Superiore di Pisa prefer to work on their PhDs somewhere else, and most likely abroad. This is great, but history shows that not many of those people will make the trip back to Italy to bring back to my home country the experience they have amassed abroad.
One of the online comments to the Nature news item reads:
Usually Italian scientists working in Italy are the best one.Italy is indeed a lovely place to live. However, data like the aforementioned ones seems to indicate that it is not quite correct to say an Italian scientist won't go abroad if (s)he can remain in Italy. A look at at the list of people I compiled off the top of my head while writing this post indicates otherwise. The writer of that comment might ask himself why foreign researchers do not consider Italy as an attractive working place despite being a lovely place to live. The answer won't be pretty.
In fact, an Italian scientist will not go abroad for a Ph.D. or postdoc
if she/he can remain in Italy with a good salary.
This is due to the fact that Italy is a wonderful place to live. So, it is true that in Italy there are very few research positions
but they are usually occupied by the best ones.
As an Italian abroad, I sincerely hope that things will change soon.
Friday, February 02, 2007
Advertisement for Deanship

As promised in a previous post, here is the "call for dean" just issued by the School of Science and Engineering at Reykjavík University. I am curious to see what applicants we'll get. (Note: I am not a member of the evaluation committee :-))
Corrigendum 4/2/2007: The deadline for applications is 1 March 2007, and not 15 February 2007, as incorrectly stated in the above announcement.
Thursday, February 01, 2007
New Chair for the Etaps Steering Committee
Wednesday, January 31, 2007
Bourbaki
For one, I did not know that André Weil (1906-1998) introduced the symbol for the empty set that we now universally use. (A whole issue of the Notices of the AMS is devoted to Weil.) Nor did I know that Boubarki coined the terms injection, surjection and bijection, and invented the notion of filter. Not to mention the striking similarity between André Weil and Eugenio Moggi! (Eugenio, I hope that you don't mind me mentioning this!)
More seriously, I really enjoyed reading that book, and I warmly recommend it. It tells what was good, and what was bad, with Bourbaki and its view of mathematics. It is also full of eminently quotable sentences from the Bourbaki members. Examples?
"You can't do good work in applied mathematics until you can do good work in pure mathematics." (Jean Dieudonné (1906-1992), cited on p. 119)
"[...] logic is the mathematician's hygiene, but it does not provide his meals. The big problems constitute the daily bread on which he lives." (André Weil in The Future of Mathematics, 1948) Shame on you Weil!
The closing paragraph of the book is poignant:
"Despite some mistakes, Bourbaki did add a little to the "honour of the human spirit." In an era when sports and money are such great idols of civilization, this is no small virtue."
Indeed, not to mention that the members of Bourbaki have included some of the greatest mathematical minds of the last century.
Great minds can also make great mistakes (for instance, Bourbaki's disdain of probability theory had a very negative effect on French work in that very important area of mathematics, and Bourbaki was very dogmatic in his view of mathematics), and one of the virtues of the book is that these are not swept under the carpet. Read it, and form your own opinion on this non-existent, and most prolific mathematician.
Friday, January 26, 2007
Change of Dean
A five-person evaluation committee will be formed by early next month, and its first assignment will be to set down criteria for the selection of the new dean for the School. I expect that an advertisement for the position will be published in early March.
Watch this space if you are interested in the job!
Trying to Influence Research Funding in Iceland
In case anybody is interested, I posted an entry entitled More Funding and More Variety! In that post I sing the praise of some types of funding that is available in countries like The Netherlands and Denmark, but not in Iceland. Comments are most welcome.
Sunday, January 21, 2007
Too Many People Have Way Too Much Money
I just heard that the director of Samskip, one of the local new rich man, has just turned 50. For his birthday, he had Elton John sing for his guests. Cost: over 100 million ISK (about 1,110,789 euros)! This is one sixth of the annual budget of the Icelandic research council. I estimate that, with that money, I could hire at least 11 visiting professors for a year, changing the face of my department.
Life is not fair.
Thursday, January 18, 2007
Lack of Funding for Italian Researchers Logic
Over the last few days, I have been reading a sequence of messages posted on the mailing list of the Italian Association for Logic and its Applications (AILA) related to the results of the applications for PRIN projects. (I think that PRIN is an Italian acronym standing for "Projects of National Interest".) The list of PRIN projects funded in the subject area of mathematics and computer science is here. A quick browse through the list gives me the impression that not enough of the funded projects are from computer science. Moreover, the only funded project related to logic in computer science is
| OMODEO Eugenio | Università degli Studi di TRIESTE | 22.680 | Sviluppo su grande scala di dimostrazioni certificate |
(Large scale development of certified proofs. Amount: 22.680 euros.)
One can also make the case that the project
| DEGANO Pierpaolo | Università degli Studi di PISA | 94.500 | Sistemi e calcoli di ispirazione biologica e loro applicazioni -- BISCA |
impacts on logic in computer science, broadly construed. (By the way, well done Pierpaolo!)
Funding for projects in mathematical logic and its relationships to computer science is conspicuously absent, despite the strength of Italian researchers in this area. Albeit the lack of funding will have very negative consequences on logic research in Italy, this is not the only thing that is bothering Italian logicians. From what I gather, all of the projects proposals from logicians received the same one-line evaluation, namely interesting, but marginal, as well as the same numerical score.
I do not know who the reviewers of the projects were, and I know nothing about the quality of the submitted projects. However, I feel that I have to take a firm and public stance against this uniform, general and vague "scientific" evaluation for 50-page long proposals. Would any of us be happy to write a long paper and have it rejected with a one-liner? And can logic research be at all labelled as being marginal?
Logic is the calculus of computer science! Apart from its intrinsic scientific and cultural interest, this fact alone shows that logic research is by no means marginal. In fact, thanks to its close connections with computer science, logic is the most applied branch of mathematics! (This is not just the opinion of your truly. I invite Italian readers --- assuming they exist, of course :-) --- to check out pages 108-109 of the interview with Enrico Giusti in the excellent book Professione Matematico. Note that Giusti is not a logician.)
I hope that the Italian mathematical community does not consider logic a marginal subject, and that, in the future, the evaluation of project proposals will involve expert reviewers from abroad, as it is done essentially everywhere else. This will be a great step forward towards the use of proper peer review in the distribution of the funding available for scientific research, and will increase the transparency of the whole process.
Wednesday, January 17, 2007
A Flurry of Prizes in Maths
The AMS has instead awarded its prizes for 2007. Once more the AMS-MAA-SIAM Morgan Prize for Outstanding Research by an Undergraduate Student went to an MIT student, Daniel Kane. It is humbling experience to see that this BSc student has already about 16 papers under his belt :-(
The February 2007 issue of the Notices is out. It features an interview with Lennart Carleson coauthored by my former Aalborg colleague Martin Raussen, and a beautiful book review Symmetry and the Monster: One of the Greatest Quests of Mathematics--A Book Review by Robert Griess. I liked it so much that I could not resist buying the book today. I might report on the book when I read it.
Sunday, January 14, 2007
Three Billion Down the Drain?
The heart of the plan is an increase in governmental funding to the University of Iceland amounting to 640 million ISK a year over the next five years (roughly 7 million euro a year). It is not completely clear to me yet what milestones the University of Iceland will have to meet to justify this investment of tax payers money. What is, however, abundantly clear is that the main competitor of the university I am working for right now (Reykjavík University) is much more powerful now than it was only four days ago, provided they will make good use of the extra funding. If previous events are anything to go by, this is very unlikely to happen in computer science unless the CS department at the University of Iceland is forced to hire according to the qualifications of the applicants.
Iceland being what it is, even your truly decided to enter the political arena for a few minutes by writing the following email message:
Subject: Financing Universities and Research
Dear Minister of Education,
It is an excellent idea to increase the level of funding for universities and research in Iceland. It is also a positive step to have some form of financing that is not linked to specific, and often narrow, project work. This is done in many other countries with great benefit to the level and quality of research. It is, however, very unclear at best that donating a large sum of money to HI the way the Ministry did yesterday is the best way to promote international quality research in Iceland.
Financial support should go to those individual researchers, research centres and laboratories where high quality academic research has been performed consistently, irrespective of the university where they are located. Allocation of resources should be made based on merit, as established by fair and objective peer review. Centuries of scientific work have shown that this is the best, if not the only, way to ensure that whatever support is available be used in the best possible way.
By way of analogy, I invite you to consider the choice of an investment fund where to invest some of your savings. Before choosing one, you would most likely examine the interests that specific funds have guaranteed their customers over the last few years. Why are political decisions on how to invest in research not based on the same principles?
Sincerely Yours,
Luca Aceto
Do I expect to receive any answer? Certainly not, but, as present head of the CS department at Reykjavík University, I felt like I had to write to the Minister on behalf of my colleagues.
I'll write a post with my first views on the HoD job over the next few days. Not surprisingly, the executive summary will be that the job is a huge time sink :-(
Friday, January 12, 2007
Concurrency Column for February 2007
The piece is loosely based on three posts I wrote for this blog. (Parts 1, 2 and 3.) This is the first time that I use this blog as a a sort of scratchpad while planning the writing of a paper. I think that I'll experiment with this use of the blog again in the future---assuming that I have anything at all to write about, that is.
Saturday, January 06, 2007
Quality of Life of Researchers in Italy
I just read an article in La Repubblica that adds fuel to the fire. (The article is in Italian.) According to a report commissioned by the trade union Nidil Cgil, Italian researchers earn on average between 800 and 1.200 euro per month before taxes. Moreover 31% of the people interviewed by the report writers earns less than 800 euro per month after taxes. It is not surprising to read that those who do not have permanent positions yet are not optimistic about their futures. About 25% of the people who do not have a permanent position are over 35 years old, and half of those are over 40. (At this age, in most other countries other you have a tenured position of some sort or you have found a different type of job altogether.) This uncertainty about the future has obvious repercussions on the quality of life, and on family planning. It turns out that 82% of the interviewees do not have children.
How can this be at all good for my own country? And why doesn't Italian society see that it is undermining its own future by not supporting the researchers who work in Italy? Can Italy ever attract foreign researchers by offering those wages? Of course, money is not everything, but it does help, and is necessary to lead a decent life. Surprise, surprise: researchers are fully fledged human beings, with human needs and desires!
Post Scriptum: The article I am refererring to also has statistics regarding the long working hours of researchers. I chose not to focus on those statistics at all here because, in my modest experience, this is the norm, rather than the exception, throughout. My present dean often tells me that "academic freedom is not the freedom of doing nothing", to which I always reply that academics have often much longer working hours than many other people.
Wednesday, January 03, 2007
Back to the Future
Others have done a great "2006 rewind" for complexity theory and mathematics. (From the latter blog, I encourage you to read the opinions on category theory. Savour John Baez's one liner `I hope most mathematicians continue to fear and despise category theory, so I can continue to maintain a certain advantage over them.')
I encourage all of us to learn from Lance Fortnow's advice on how to deliver a job talk. That piece of advice, and the comments to the post, apply to any talk, not just our job talks.
Finally, I hope that during this year I'll follow the following piece of advice from Allan Bay, an Italian cook and food writer, whose sixth piece of advice in Cuochi Si Diventa (one of my favourite cookbooks) reads:
Cook with calm; haste and anxiety are your worst advisors. If you know you have little time, opt for a quick recipe, one that you can cook as well as you can in the little time you have at your disposal. This virtue is useful well beyond your kitchen....
Indeed, haste and anxiety are usually not conducive to good research work either. (The advice we give others is the advice we ourselves need.)
Hopefully 2007 will be a great year for concurrency theory, ICE-TCS, all of my collaborators and friends, and, why not, a decently productive one for me too. I wish that I could begin by attending this talk :-)