Monday, November 28, 2022

The World Dynamics Project

Our colleagues Pierluigi Crescenzi, Emanuele Natale and Paulo Bruno Serafim have been doing some work on what they call the World Dynamics project, whose goal is to provide a modern framework for studying models of sustainable development, based on cutting-edge techniques from software engineering and machine learning. 

The first outcome of their work is a Julia library that allows scientists to use and adapt different world models, from Meadows et al.'s World3 to recent proposals, in an easy way.

IMHO, this is a fascinating and timely research effort. I encourage readers of this blog to try the current version of the Julia library, which is still under development. It would be great if this library contributed to "an open, interdisciplinary, and consistent comparative approach to scientific model development" and I hope that global policy makers on environmental and economic issues will use similar tools in the nearest future.

Thanks to Emanuele, Paulo and Pierluigi for their work. I'll be following its future development with great interest.

If you speak Italian, I strongly recommend this podcast, in the GSSI-SISSA Sidecar series, in which Pierluigi discusses economic growth with Michele Boldrin.

Saturday, November 12, 2022

Two faculty positions in Computer Science at Reykjavik University

My department has advertised two full-time, permanent faculty positions at any rank . Theoretical Computer Science is not the department's highest priority in hiring at this moment in time, but it is mentioned as one of the areas of interest, alongside Artificial Intelligence, Cybersecurity, Data Science and Machine Learning, and Software Engineering. Do consider applying if you are theoretically minded, your work has, or has the potential to have, impact on any of those fields, and you'd like to join our academic family and relocate to Iceland. The call is below and at https://jobs.50skills.com/ru/en/16728, where the application form can be found.

Two faculty positions in Computer Science at Reykjavik University

The Department of Computer Science at Reykjavik University invites applications for two full-time, permanent faculty positions at any rank in the fields of Artificial Intelligence, Cybersecurity, Data Science and Machine Learning, Software Engineering, and Theoretical Computer Science. For one of the positions, we will give preferential treatment to excellent applicants in Software Engineering, broadly construed. However, the primary evaluation criterion is scientific quality. Outstanding candidates in other areas of Computer Science are encouraged to apply as well. See https://jobs.50skills.com/ru/en/16728 for the link to the application form.  

We are looking for energetic, highly qualified academics with a proven international research record and excellent potential in their field of study. We particularly welcome applications from researchers who have a strong network of research collaborators, can strengthen internal collaborations within the department, have the proclivity to improve their academic environment and its culture, and have the drive and potential to flourish in our environment. The Department of Computer Science at Reykjavik University is characterised by a flat hierarchical structure and every faculty member is expected to act like a principal investigator regardless of their level of employment.  
 
Apart from developing their research career, the successful applicants will play a full part in the teaching and administrative activities of the department, teaching courses and supervising students at both graduate and undergraduate level. Applicants with a demonstrated history of excellence in teaching are preferred.
 
Salary and rank are commensurate with experience. Successful applicants receive a relocation budget, some seed research funding in the first two years of their employment and support for one PhD student. Among other benefits, Reykjavik University offers its research staff the option to take research semesters (sabbaticals) every three years of satisfactory teaching and research activity and provides some additional financial support during those semesters.  
 
The positions are open until filled, with intended starting date in August 2023. Later starting dates can be negotiated, but preference will be given to candidates who can take up their position in August 2023. The deadline for applications is January 27, 2023. The review of the applications will begin in late January 2023 and will continue until the positions are filled.
 
A PhD in Computer Science or a related field is required. Applications should be submitted through the university’s online application submission system and should include the following documents:

  • a cover letter specifying whether the candidate is applying for appointment as an assistant, associate, or full professor,
  • a CV with a full list of publications, 
  • links to three to five major publications, 
  • a research statement, 
  • a teaching statement, 
  • supporting material regarding excellence in teaching, if available, and 
  • any other relevant information the applicant wishes to supply.
Please arrange to have three letters of recommendation sent directly to mannaudur@ru.is (subject “Faculty Positions in CS”) with a copy to Professor Luca Aceto (luca@ru.is), Chair of the Department of Computer Science. Informal communication and discussions on any aspect related to the positions are encouraged, and interested candidates are welcome to contact the chair of the search committee, Associate Professor María Óskarsdóttir (mariaoskars@ru.is), for further information.
 
Department of Computer Science at Reykjavik University
 
The Department of Computer Science at Reykjavik University is research intensive and carries out research-based teaching in all its degree programmes. It offers undergraduate and graduate programs in Computer Science and Software Engineering, a combined undergraduate program in Discrete Mathematics and Computer Science, two graduate programs in Data Science and one in Artificial Intelligence and Language Technology. From the autumn semester 2023, the department will also offer an MSc in Digital Health. At the time of writing, it is home to 26 faculty members, seven of whom are women, five postdoctoral researchers, and 32 PhD students representing altogether over 20 different countries. In 2022, the department had 740 students registered for its BSc and MSc programmes.

The department provides an excellent working environment in which a motivated academic can have an impact at all levels and has a career-development framework that encourages and supports independence in academic endeavours.  

The department is home to several research centres producing high-quality collaborative research in areas such as artificial intelligence, data science, financial technology, information systems, language technology, software systems, and theoretical computer science, among others; for more information on those research centres, see https://en.ru.is/research/.
 
For further information about the Department of Computer Science at Reykjavik University and its activities, see http://en.ru.is/scs/.
 
Reykjavík University
 
On the Times Higher Education rankings for 2023, Reykjavik University is ranked among the 350 best universities world-wide, first among Icelandic universities, and 18th among Nordic ones. Moreover, it was ranked 12th amongst the best small universities in the Times Higher Education rankings 2022, when it was in first place along with eight other universities for the average number of citations per faculty and 53rd amongst all universities established fewer than 50 years ago.  
 
Iceland

Iceland is well known for breathtaking natural beauty, with volcanoes, hot springs, lava fields and glaciers offering a dramatic landscape. It consistently ranks as one of the best places in the world to live. It offers a high quality of life, is one of the safest places in the world, with high gender equality, and strong healthcare and social-support systems. It was in second position in the 2021 UN World Happiness Report, which correlates with various life factors. Reykjavik is a vibrant and cosmopolitan city, which provides an ideal environment for combining cultural and family activities with an active lifestyle.

Monday, September 19, 2022

Dean of the School of Technology at Reykjavik University: Call for applications

Reykjavik University is looking for a new dean of the School of Technology, which comprises the Department of Applied Engineering, the Department of Computer Science, and the Department of Engineering. 

If you have a strong academic career, a vision of how our school can improve its standing and impact, and would enjoy living in Iceland, I encourage you to consider this opportunity! See the ad at the link below for more information: 

https://jobs.50skills.com/ru/en/15613 

Spread the news through your network and encourage excellent candidates to apply.

Wednesday, August 10, 2022

CONCUR through time: A data- and graph-mining analysis

The 33rd edition of the International Conference on Concurrency Theory (CONCUR) will be held in Warsaw, Poland, in the period 16–19 September 2022. The first CONCUR conference dates back to 1990 and was one of the conferences organized as part of the two-year ESPRIT Basic  Research  Action  3006  with  the  same  name.   The  CONCUR  community  has  run  the conference ever since and established the IFIP WG 1.8 “Concurrency Theory” in 2005 under Technical Committee TC1 Foundations of Computer Science of IFIP1.

In light of the well-established nature of the CONCUR conference, and spurred by a data-and graph-mining comparative analysis carried out by Pierluigi Crescenzi and three of his students to celebrate the 50th anniversary of ICALP, Pierluigi and I undertook a similar study for the CONCUR conference using some, by now classic, tools from network science.  Our goal was to try and understand the evolution of the CONCUR conference throughout its history, the ebb and flow in the popularity of some research areas in concurrency theory, and the centrality of CONCUR authors, as measured by several metrics from network science, amongst other topics. 

Our article available here reports on our findings.  We hope that members of the CONCUR community will enjoy reading it and playing with the web-based resources that accompany this piece.  It goes without saying that the data analysis we present has to be taken with a huge pinch of salt and is only meant to provide an overview of the evolution of CONCUR and to be food for thought for the concurrency theory community.

Tuesday, August 09, 2022

Interview with Franck Cassez and Kim G. Larsen, CONCUR 2022 ToT Award Recipients

This post is devoted to an interview with Kim G. Larsen, who received the CONCUR 2022 Test-of-Time Award for the paper The Impressive Power of Stopwatches (available also here), which appeared at CONCUR 2000 and was co-authored with Franck Cassez. On behalf of the concurrency theory community, I thank Kim for taking the time to answer my questions. I trust that readers of this blog will enjoy reading Kim's answer as much as I did. 

Luca: You receive the CONCUR ToT Award 2022 for your paper  The Impressive Power of Stopwatches, which appeared at CONCUR 2000. In that article, you showed that timed automata enriched with stopwatches and unobservable time delays have the same expressive power of  linear hybrid automata. Could you briefly explain to our readers what timed automata with stopwatches are? Could you also tell us how you came to study the question addressed in your award-winning article? Which of the results in your paper did you find most surprising or challenging?

Kim: Well, in timed automata all clocks grow with rate 1 in all locations of the automata. Thus you can tell the amount of time that has elapsed since a particular clock was last reset, e.g. due to an external event of interest.  A stopwatch is a real-valued variable similar to a regular clock.  In contrast to a clock, a stopwatch will in certain locations grow with rate 1 and in other locations grow with rate 0, i.e. it is stopped.  As such, a stopwatch gives you information about the accumulated time spent in a certain parts of the automata. 

In modelling schedulability problems for real-time systems, the use of stopwatches is crucial in order to adequately capture preemption.   I definitely believe that it was our shared interest in schedulability that brought us to study timed automata with stopwatches.  We knew from earlier results by Alur et al. that properties such as reachability was undecidable. But what could we do about this? And how much expressive power would the addition of stopwatches provide?

In the paper we certainly put the most emphasis on the latter question, in that we showed that stopwatch automata and linear hybrid automata accept the same class of timed languages, and this was at least for me the most surprising and challenging result. However, focusing on impact, I think the approximate zone-based method that we apply in the paper has been extremely important from the point of view of having our verification tool UPPAAL being taken-up at large by the embedded systems community.  It has been really interesting to see how well the over-approximation method actually works.

Luca: In your article, you showed that linear hybrid automata and stopwatch automata accept the same class of timed languages. Would this result still hold if all delays were observable? Do the two models have the same expressive power with respect to finer notions of equivalence such as timed bisimilarity, say? Did you, or any other colleague, study that problem, assuming that it is an interesting one?

Kim:  These are definitely very interesting questions, and should be studied.  As for finer notions of equivalences – e.g. timed bisimilarity – I believe that our translation could be shown to be correct up to some timed variant of chunk-by-chunk simulation introduced by Anders Gammelgaard in his Licentiat Thesis from Aarhus University in 1991.  That could be a good starting point.


Luca: Did any of your subsequent research build explicitly on the results and the techniques you developed in your award-winning paper?
Which of your subsequent results on timed and hybrid automata do you like best? Is there any result obtained by other researchers that builds on your work and that you like in particular or found surprising?

Kim:  Looking up in DBLP, I see that I have some 28 papers containing the word “scheduling”.  For sure stopwatches will have been used in one way or another in these.  One thing that we never really examined thoroughly is to investigate how well the approximate zone-based will worked when applied to the translation of linear hybrid automata through the translation to stopwatch automata.  This would definitely be interesting to find out. 

This was the first joint publication between me and Franck.  I enjoyed fully the collaboration on all the next 10 joint papers.  Here the most significant ones are probably the paper at CONCUR 2005, where we presented the symbolic on-the-fly algorithms for synthesis for timed games and the branch UPPAAL TIGA.  And later in a European project GASICS with Jean-Francois Raskin, we used the TIGA in the synthesis of optimal and robust control of a hydraulic system.

Franck: Using the result in our paper, we can analyse scheduling problems where tasks can be stopped and restarted, using real-time model-checking and a tool like UPPAAL.


To do so, we build a network of stopwatch automata modelling the set of tasks and a scheduling policy, and reduce schedulability to a safety verification problem: avoid reaching states where tasks do not meet their deadlines. Because we over-approximate the state space, our analysis may yield some false positives and may wrongly declare a set of tasks non-schedulable because the over-approximation is too coarse. 

In the period 2003–2005, in cooperation with Francois Laroussinie we tried to identify some classes of stopwatch automata for which the over-approximation does not generate false positives.  We never managed to find an interesting subclass. 

This may look like a serious problem in terms of applicability of our result, but in practice, it does not matter too much. Most of the time, we are interested in the schedulability of a specific set of tasks (e.g. controlling a plant, a car, etc.) and for these instances, we can use our result: if we have false positives, we can refine the model tasks and scheduler and rule them out. Hopefully after a few iterations of refinement, we can prove that the set of tasks is schedulable.

The subsequent result on timed and hybrid automata of mine  that I probably like best is the one we obtained on solving optimal reachability in timed automata.
We had a paper at FSTTCS in 2004 presenting the theoretical results, and a companion paper at GDV 2004 with an implementation using HyTech, a tool for analysing hybrid automata. 

I like these results because we ended up with a rather simple proof, after 3-4 years working on this hard problem. 

Luca:  Could you tell us how you started your collaboration on the award-winning paper? I recall that Franck was a regular visitor to our department at Aalborg University for some time, but I can't recall how his collaboration with the Uppaal group started.  

Kim: I am not quite sure I remember how and when I first met Franck.  For some time we already worked substantially with French researchers, in particular from LSV Cachan (Francois Larroussinie and Patricia Bouyer).   I have the feeling that there were quite some strong links between Nantes (were Franck was) and LSV on timed systems in those days.  Also Nantes was the organizer of the PhD school MOVEP five times in the period 1994-2002, and I was lecturing there in one of the years, meeting Olivier Roux and Franck who were the organizers.   Funny enough, this year we are organizing MOVEP in Aalborg. Anyway, at some point Franck became a regular visitor to Aalborg, often for long periods of time – playing on the Squash team of the city when he was not working.

Franck: As Kim mentioned, I was in Nantes at that time, but I was working with Francois Laroussinie who was in Cachan. Francois had spent some time in Aalborg working with Kim and his group and he helped organise a mini workshop with Kim in 1999, in Nantes. That’s when Kim invited me to spend some time in Aalborg, and I visited Aalborg University for the first time from October 1999 until December 1999. This is when we worked on the stopwatch automata paper. We wanted to use UPPAAL to verify systems beyond timed automata. 

I visited Kim and his group almost every year from 1999 until 2007, when I moved to Australia. There were always lots of visitors at Aalborg University and I was very fortunate to be there and learn from the Masters. 

I always felt at home at Aalborg University, and loved all my visits there. The only downside was that I never managed to defeat Kim at badminton. I thought it was a gear issue, but Kim gave me his racket (I still have it) and the score did not change much.


Luca: What are the research topics that you find most interesting right now?
Is there any specific problem in your current field of interest that you'd like to see solved?

Kim: Currently I am spending quite some time on marrying symbolic synthesis with reinforcement learning for Timed Markov Decision Processes in order to achieve optimal as well as safe strategies for Cyber-Physical Systems.


Luca: Both Franck and you have a very strong track record in developing theoretical results and in applying them to real-life problems.
In my, admittedly biased, opinion, your work exemplifies Ben Schneiderman's Twin-Win Model (https://www.pnas.org/doi/pdf/10.1073/pnas.1802918115), which propounds the pursuit of "the dual goals of breakthrough theories in published papers and validated solutions that are ready for widespread dissemination." Could you say a few words on your research philosophy?

Kim: I completely subscribe to this.  Several early theoretically findings – as the paper on stopwatch automata – have been key in our sustainable transfer to industry.

Franck: Kim has been a mentor to me for a number of years now, and I certainly learned this approach/philosophy from him and his group. 
 

We always started from a concrete problem, e.g. scheduling tasks/checking schedulability, and to validate the solutions, building a tool to demonstrate applicability. The next step was to improve the tool to solve larger and larger problems.


UPPAAL is a fantastic example of this philosophy: the reachability problem for timed automata is PSPACE-complete. That would deter a number of people to try and build tools to solve this problem.  But with smart abstractions, algorithms and data-structures, and constant improvement over a number of years, UPPAAL can analyse very large and complex systems. It is amazing to see how UPPAAL is used in several areas from traffic control to planning and to precisely guiding a needle for an injection. 


Luca: What advice would you give to a young researcher who is keen to start working on topics related to formal methods?

Kim: Come to Aalborg, and participate in year's MOVEP.

Friday, July 29, 2022

Davide Sangiorgi's Interview with James Leifer, CONCUR 2022 ToT Award Recipient

I am pleased to post Davide Sangiorgi's interview with CONCUR 2022 Test-of-Time Award recipient James Leifer, who will receive the award for the paper
"Deriving Bisimulation Congruences for Reactive Systems" co-authored with the late Robin Milner.

Thanks to James for painting a rich picture of the scientific and social context within which the work on that paper was done and to Davide for conducting the interview. I trust that readers of this blog will enjoy reading it as much as I did.

Davide: How did the work presented in your CONCUR ToT paper come about?

James: I was introduced to Robin Milner by my undergraduate advisor Bernard Sufrin around 1994. Thanks to that meeting, I started with Robin at Cambridge in 1995 as a fresh Ph.D. student. Robin had recently moved from Edinburgh and had a wonderful research group, including, at various times, Peter Sewell, Adriana Compagnoni, Benjamin Pierce, and Philippa Gardner. There were also many colleagues working or visiting Cambridge interested in process calculi: Davide Sangiorgi, Andy Gordon, Luca Cardelli, Martín Abadi,... It was an exciting atmosphere! I was particularly close to Peter Sewell, with whom I discussed the ideas here extensively and who was generous with his guidance.

There was a trend in the community at the time of building complex process calculi (for encryption, Ambients, etc.) where the free syntax would be quotiented by a structural congruence to "stir the soup" and allow different parts of a tree to float together; reaction rules (unlabelled transitions) then would permit those agglomerated bits to react, to transform into something new.

Robin wanted to come up with a generalised framework, which he called Action Calculi, for modelling this style of process calculi.  His framework would describe graph-like "soups" of atoms linked together by arcs representing binding and sharing; moreover the atoms could contain subgraphs inside of them for freezing activity (as in prefixing in the pi-calculus), with the possibility of boundary crossing arcs (similarly to how nu-bound names in pi-calculus can be used in deeply nested subterms).  

Robin had an amazing talent for drawing beautiful graphs! He would "move" the nodes around on the chalkboard and reveal how a subgraph was in fact a reactum (the LHS of an unlabelled transition).  In the initial phases of my Ph.D. I just tried to understand these graphs: they were so natural to draw on the blackboard! And yet, they were also so uncomfortable to use when written out in linear tree- and list-like syntax, with so many distinct concrete representations for the same graph.

Putting aside the beauty of these graphs, what was the benefit of this framework? If one could manage to embed a process calculus in Action Calculi, using the graph structure and fancy binding and nesting to represent the quotiented syntax, what then? We dreamt about a proposition along the following lines: if you represent your syntax (quotiented by your structural congruence) in Action Calculi graphs, and you represent your reaction rules as Action Calculi graph rewrites, then we will give you a congruential bisimulation for free!

Compared to CCS for example, many of the rich new process calculi lacked labelled transitions systems. In CCS, there was a clean, simple notion of labelled transitions and, moreover, bisimulation over those labelled transitions yielded a congruence: for all processes P and Q, and all process contexts C[-], if P ~ Q, then C[P] ~ C[Q]. This is a key quality for a bisimulation to possess, since it allows modular reasoning about pieces of a process, something that's so much harder in a concurrent world than in a sequential one.

Returning to Action Calculi, we set out to make good on the dream that everyone gets a congruential bisimulation for free! Our idea was to find a general method to derive labelled transitions systems from the unlabelled transitions and then to prove that bisimulation built from those labelled transitions would be a congruence.

The idea was often discussed at that time that there was a duality whereby a process undergoing a labelled transition could be thought of as the environment providing a complementary context inducing the process to react. In the early labelled transition system in pi-calculus for example, I recall hearing that P undergoing the input labelled transition xy could be thought of as the environment outputting payload y on channel x to enable a tau transition with P.

So I tried to formalise this notion that labelled transitions are environmental contexts enabling reaction, i.e. defining P ---C[-]---> P' to mean C[P] ------> P' provided that C[-] was somehow "minimal", i.e. contained nothing superfluous beyond what was necessary to trigger the reaction. We wanted to get a rigorous definition of that intuitive idea. There was a long and difficult period (about 12 months) wandering through the weeds trying to define minimal contexts for Action Calculi graphs (in terms of minimal nodes and minimal arcs), but it was hugely complex, frustrating, and ugly and we seemed no closer to the original goal of achieving congruential bisimulation with these labelled transitions systems.

Eventually I stepped back from Action Calculi and started to work on a more theoretical definition of "minimal context" and we took inspiration from category theory.  Robin had always viewed Action Calculi graphs as categorical arrows between objects (where the objects represented interfaces for plugging together arcs). At the time, there was much discussion of category theory in the air (for game theory); I certainly didn't understand most of it but found it interesting and inspiring.

If we imagine that processes and process-contexts are just categorical arrows (where the objects are arities) then context composition is arrow composition. Now, assuming we have a reaction rule R ------> R', we can define labelled transitions P ---C[-]---> P' as follows: there exists a context D such that C[P] = D[R] and P' = D[R']. The first equality is a commuting diagram and Robin and I thought that we could formalise minimality by something like a categorical pushout! But that wasn't quite right as C and D are not the minimum pair (compared to all other candidates), but a minimal pair: there may be many incomparable minimal pairs all of which are witnesses of legitimate labelled transitions.  There was again a long period of frustration eventually resolved when I reinvented "relative pushouts" (in place of pushouts). They are a simple notion in slice categories but I didn't know that until later...

Having found a reasonable definition of "minimal", I worked excitedly on bisimulation, trying to get a proof of congruence: P ~ Q implies E[P] ~ E[Q]. For weeks, I was considering the labelled transitions of E[P] ---F[-]---> and all the ways that could arise. The most interesting case is when a part of P, a part of E, and F all "conspire" together to generate a reaction. From that I was able to derive a labelled transition of P by manipulating relative pushouts, which by hypothesis yielded a labelled transition of Q, and then, via a sort of "pushout pasting", a labelled transition E[Q] ---F[-]--->. It was a wonderful moment of elation when I pasted all the diagrams together on Robin's board and we realised that we had the congruence property for our synthesised labels!

We looked back again at Action Calculi, using the notion of relative pushouts to guide us (instead of the arbitrary approach we had considered before) and we further looked at other kinds of process calculi syntax to see how relative pushouts could work there...  Returning to the original motivation to make Action Calculi a universal framework with congruential bisimulation for free, I'm not convinced of its utility. But it was the challenge that led us to the journey of the relative pushout work, which I think is beautiful.

Davide: What influence did this work have in the rest of your career? How much of your subsequent work built on it?

James: It was thanks to this work that I visited INRIA Rocquencourt to discuss process calculi with Jean-Jacques Lévy and Georges Gonthier. They kindly invited me to spend a year as postdoc in 2001 after I finished my thesis with Robin, and I ended up staying in INRIA ever since. I didn't work on bisimulation again as a research topic, but stayed interested in concurrency and distribution for a long time, working with Peter Sewell et al on distributed language design with module migration and rebinding, and with Cédric Fournet et al on compiler design for automatically synthesising cryptographic protocols for high level sessions specifications.

Davide: Could you tell us about your interactions with Robin Milner? What was it like to work with him? What lessons did you learn from him?

James: I was tremendously inspired by Robin.

He would stand at his huge blackboard, his large hands covered in chalk, his bicycle clips glinting on his trousers, and he would stalk up and down the blackboard --- thinking and moving.  There was something theatrical and artistic about it: his thinking was done in physical movement and his drawings were dynamic as the representations of his ideas evolved across the board.

I loved his drawings. They would start simple, a circle for a node, a box for a subgraph, etc. and then develop more and more detail corresponding to his intuition. (It reminded me of descriptions I had read of Richard Feynman drawing quantum interactions.)

Sometimes I recall being frustrated because I couldn't read into his formulas everything that he wanted to convey (and we would then switch back to drawings) or I would be worried that there was an inconsistency creeping in or I just couldn't keep up, so the board sessions could be a roller coaster ride at times!

Robin worked tremendously hard and consistently. He would write out and rewrite out his ideas, regularly circulating hand written documents. He would refine over and over his diagrams. Behind his achievements there was an impressive consistency of effort.

He had a lot of confidence to carry on when the sledding was hard. He had such a strong intuition of what ought to be possible, that he was able to sustain years of effort to get there.

He was generous with praise, with credit, with acknowledgement of others' ideas. He was generous in sharing his own ideas and seemed delighted when others would pick them up and carry them forward. I've always admired his openness and lack of jealousy in sharing ideas.

In his personal life, he seemed to have real compatibility with Lucy (his wife), who also kept him grounded. I still laugh when I remember once working with him at his dining room table and Lucy announcing, "Robin, enough of the mathematics. It's time to mow the lawn!"

I visited Oxford for Lucy's funeral and recall Robin putting a brave face on his future plans; I returned a few weeks later when Robin passed away himself. I miss him greatly. 

Davide: What research topics are you most interested in right now? How do you see your work develop in the future?

James: I've been interested in a totally different area, namely healthcare, for many years. I'm fascinated by how patients, and information about them, flows through the complex human and machine interactions in hospital. When looking at how these flows work, and how they don't, it's possible to see where errors arise, where blockages happen, where there are informational and visual deficits that make the job of doctors and nurses difficult. I like to think visually in terms of graphs (incrementally adding detail) and physically moving through the space where the action happens --- all inspired by Robin!

Tuesday, July 05, 2022

ICALP and the EATCS turn 50

These days, our colleagues at IRIF are hosting ICALP 2022 in Paris. This is the 49th edition of the ICALP conference, which turns 50 since its first instalment was held in 1972. ICALP was the first conference of the, then newly founded, European Association for Theoretical Computer Science (EATCS).The rest is history and I let any readers this post might have draw their own conclusions on the role that the EATCS and ICALP have played in supporting the development of theoretical computer science. (Admittedly, my opinions on both the EATCS and ICALP are very biased.) 

The scientific programme of ICALP 2022 is mouthwatering as usual, thanks to the work done by the authors of submitted papers, Mikołaj Bojańczyk and David Woodruff (PC chairs), and their PCs. I encourage everyone to read the papers that are being presented at the conference.

The main purpose of this post, however, is to alert the readers of this blog that ICALP 2022 also hosts an exhibition to celebrate EATCS/ICALP at 50 and theoretical computer science at large. If you are in Paris, you can attend the exhibition in person. Otherwise, you can visit it virtually here. (See also the posters in one PDF file.)

I had the honour to take part in the preparation of the material for that exhibition, which was led by Sandrine Cadet and Sylvain Schmitz. I learnt a lot from all the other colleagues in the committee for the exhibition. 

As part of that work, I asked Pierluigi Crescenzi whether he'd be willing to carry out a graph and data mining analysis of ICALP vis-a-vis other major conferences in theoretical computer science based on DBLP data. Pierluigi's work went well beyond the call of duty and is summarised in this presentation. I trust that you'll find the results of the analysis by Pierluigi and three of his students at the Gran Sasso Science Institute very interesting. If you have any suggestions for expanding that analysis further, please write it in the comment section. 

Let me close by wishing the EATCS and ICALP a happy 50th birthday, and a great scientific and social event to all the colleagues who are attending ICALP 2022.