Séminaire de l'IRIF

Jour et lieu : le vendredi de 10h30 à 12h00, d'habitude à l'amphi Turing, Bâtiment Sophie Germain (à confirmer dans chaque annonce)

Responsable : Adi Rosén

Le séminaire de l'IRIF se decline sous deux series: IRIF distinguished talks series et IRIF expository talks series.

Mardi 11 avril 2017 · 10h30 · Amphi Turing

Leonid Libkin (University of Edinburgh) · IRIF expository talks series: Primordial database theory revisited: are relational algebra, calculus, and basic SQL really equivalent?

We revisit one of the most basic questions of database theory: the equivalence of first-order logic (FO), relational algebra (RA), and the core of SQL. Despite being at the heart of relational theory, these questions do not have satisfactory answers in the literature. The well known equivalence of FO and RA, and existing translations from SQL to RA, work only for simple models that fall short of what real databases use. Proving results about real SQL, rather than a theoretical reconstruction, is hampered by the lack of formal SQL semantics: the Standard is too vague for the purpose, and previous attempts at formalizing SQL's semantics made many simplifying assumptions that do not hold in real life. On the logic side, SQL mixes Boolean and 3-valued logics in a way that has never been properly studied.

Our goal is to fill these surprising gaps in basic database theory. We provide a formal semantics of the core of SQL that captures the real language and accounts for many of its idiosyncrasies. To justify it as the correct semantics, we validate it experimentally on a large number of randomly generated queries. With this semantics, we formally prove the equivalence of core SQL and RA, as well as the extension of 3-valued FO with an operator that accounts for SQL's ability to switch back and forth between Boolean and 3-valued logics. Then, somewhat surprisingly, we show that this additional operator does not add expressiveness, and - even more surprisingly - that 3-valued logic does not add expressiveness even in the presence of nulls.

Based on joint work with with Paolo Guagliardo.

Vendredi 03 mars 2017 · 10h30 · Amphi Turing

Joost-Pieter Katoen (RWTH Aachen) · IRIF Distinguished Talks Series: Principles of Probabilistic Programming (click here for the slides)

Probabilistic programming is en vogue. It is used to describe complex Bayesian networks, quantum programs, security protocols and biological systems. Programming languages like C, C#, Java, Prolog, Scala, etc. all have their probabilistic version. Key features are random sampling and means to adjust distributions based on obtained information from measurements and system observations. We show some semantic intricacies, argue that termination is more involved than the halting problem, and discuss recursion and run-time analysis.

Vendredi 28 octobre 2016 · 10h30 · Salle 3052, Bâtiment Sophie Germain (SEE NOTE IN THE ABSTRACT)

Yuri Gurevich (Microsoft Research) · IRIF expository talks series : Logic in Computer Science and Computer Engineering

In software industry, engineers do formal logic day in and day out, even though they may not realize that. As a rule, they have not studied logic. Instead, they spent a lot of time studying calculus which they use rarely, if ever. I'll try to illustrate why logic is so relevant and why it is hard for software engineers to pick it up.

IMPORTANT NOTE: For administrative reasons, those from outside of IRIF who wish to attend the seminar in “Salle 3052” should email by Wednesday 26/10 their name to Irène Guessarian at ig@liafa.univ-paris-diderot.fr .

Vendredi 16 septembre 2016 · 10h30 · Amphi Turing (Bâtiment Sophie Germain)

Roberto di Cosmo (IRIF) · IRIF expository talks series: Preserving Software: challenges and opportunities for the reproductibility of Science (click here for the slides)

A vast amount of modern scientific and technological knowledge relies on the software that we have been collectively writing: deep knowledge from fields like mathematics, physics, chemistry, biology, medicine, finance and social sciences is now inextricably embodied into complex software systems, which model it at a level of detail that goes way beyond that of the usual scientific publications.

Preserving this software is of paramount importance to preserve our knowledge.

It is is a necessary prerequisite to allow the replication of experiments, which is the foundation of the scientific method, as well as to ensure our ability to modify and correct the software components that are constantly being incorporated into critical systems that need to stay in production for decades.

In this talk, we will review the challenges and opportunities we are facing, and discuss the role of Open Source as a key enabler.

The slides of the talk can be found here.

Jeudi 28 janvier 2016 · 10h30 · Amphi Turing

Nachum Dershowitz (Tel Aviv University) · Ada and Computation

Ada Lovelace (born 200 years ago) wrote presciently about digital numerical calculations. She expressed its features poetically: “We may say most aptly that [Babbage's] Analytical Engine weaves algebraical patterns just as the Jacquard loom weaves flowers and leaves.” Ada explained the generality of digital computation, saying that “the engine can arrange and combine its numerical quantities exactly as if they were letters or any other general symbols.” We will discuss some of the expected and unexpected consequences of alternate representations of computational data. On the other hand, Ada wrote that “the engine [is] the material expression of any indefinite function of any degree of generality and complexity.” This we now know was overstating her case. We will discuss the formalization of the notion of effective computation and its consequences vis-a-vis computability and complexity of computation.