# Ettekanded / Talks

#### Abel Armas-Cervantes: Event Structures as a Foundation for Process Model Differencing

Abstract: Large organizations often need to maintain several variants of a process model. Such variants may stem from distinct products, different types of customers, dissimilar legal requirements across countries, or idiosyncratic choices made by multiple business units over time. In some scenarios, analysts need to find ways to consolidate multiple process variants into a single one. In this setting, analysts need to accurately understand the differences between multiple variants in order to determine how to reconcile them.

This talk will present the current work addressing the problem of explaining the differences between a pair of acyclic process models in terms of simple and intuitive statements. The presented process model differencing takes the behavior of the processes as the aspect for comparison. The presented approach is based on two types of Event Structures (a well know formalism for expressing behavioral relations): Prime event structures and Asymmetric event structures. It is found that the high level of node duplication inherent to prime event structures hinders on the usefulness of the difference diagnostics that can be extracted thereon. Accordingly, the current approach defines a method for producing (asymmetric) event structures with reduced amount of duplication.

#### James Chapman: Time Based Art

Slides of the talk: [html]

Abstract: Time Based Art (TBA) refers to art which has a 'duration' as well as a 'dimension'. The audience watches as the installation develops before their eyes. Time Based media works demand that we shift our gaze beyond the material to embrace the less tangible aspects of an installation. This performance will be an exercise in live coding, a new comer to the time based art scene, which celebrates artists from across and in-between all mediums, and activates the entire community with art and ideas. In this performance I will code up an interpreter for Gödel's System T and use it to add two and two.

#### Robin Cockett: Complexity as Computability over Timed Sets

Slides of the talk: [pdf]

Abstract: Turing categories capture abstractly the notion of computability. A natural question to ask, therefore, is: "what categories can be the total maps of a Turing category". For example, is it possible to have a Turing category in which the total maps are precisely the polynomial time maps?

One can abstractly completely characterize categories which can be the total maps of Turing categories and this tells one that there are indeed Turing categories whose total maps belong to maps with low complexity. However, this abstract result is rather unsatisfactory as the proof is completely unrelated to complexity! The purpose of the talk is to show how one can build Turing categories with total maps belonging to various complexity classes using the basic tools of complexity theory itself!

#### Briti Deb: Regular Expression Learning for Mining Links between Gene - Environment Interactions

Abstract: The growing digital repository of scientific literature (MEDLINE) demands novel text mining approaches to search text, extract relevant terms, and understand the relationship between terms in an acceptable time and space. One such problem is mining MEDLINE to find links between genes and environmental risk factors for a disease. In this talk, I describe a novel text mining approach of using regular expression learning to recognize gene names, search co-occuring environmental risk factors, and finally construct a network between genes and environmental risk factors for a disease. Preliminary results indicate that such an approach can distill links between interesting terms from large text corpus and visualize graphically.

#### Denis Firsov: Certified normalization of context-free grammars

Abstract: Several decision procedures for context-free grammars work on grammars in some normal form. The aim of this work was to implement verified conversions between context-free grammars in general and normal forms. This was done by implementing and verifying correctness of four transformations in the Agda dependently typed programming language. These transformations can be applied independently, giving different versions of the original grammar. When all four of them are applied in the right order, then the Chomsky normal form is achieved.

The transformations were proved to be sound and complete. Soundness and completeness state that parse trees for the normalized grammar and parse trees for the original grammar are interconvertible. Since the proofs are constructive, they are in fact certified parse tree conversion programs. (Joint work with Tarmo Uustalu.)

#### Luciano García-Bañuelos: Discovering Branching Conditions from Business Process Execution Logs

Abstract: Process mining is a family of techniques to discover business process models and other knowledge of business processes from event logs. Existing process mining techniques are geared towards discovering models that capture the order of execution of tasks, but not the conditions under which tasks are executed -- also called branching conditions. One existing process mining technique, namely ProM's Decision Miner, applies decision tree learning to discover branching conditions composed of atoms of the form "v op c" where "v" is a variable, "op" is a comparison predicate and "c" is a constant. In this talk, I will present a more general technique to discover branching conditions where the atoms are linear equations or inequalities involving multiple variables and arithmetic operators. The proposed technique combines invariant discovery techniques embodied in the Daikon system with decision tree learning techniques.

#### Wolfgang Jeltsch: Abstract Process Categories

Slides of the talk: [pdf]

Abstract: Functional reactive programming (FRP) allows programs to deal with temporal aspects in a declarative way. FRP is based on behaviors and events, which denote time-varying values and values attached to times, respectively. Recently, we added the notion of process to FRP. A process combines continuous and discrete aspects and generalizes behaviors and events. In this talk, we develop a class of categorical models for FRP with processes. We call these models abstract process categories.

#### Sven Laur: Need for speed

Abstract: The presentation gives an overview of recent advances in multi-party computation. We start with a brief overview of the SPEEDZ protocol, which combines oblivious message authentication and somewhat fully homomorphic encryption to generate a massive amount of Beaver triples. In this presentation, we discuss whether the same throughput of Beaver triples can be achieved using only an additively homomorphic cryptosystem and what are the biggest performance bottlenecks.

#### Fabrizio Maggi: Declarative Process Mining

Abstract: The increasing availability of event data recorded by contemporary information systems makes process mining a valuable instrument to improve and support business processes. Starting point for process mining is an event log. Typically, three types of process mining can be distinguished: (a) process discovery (learning a model from example traces in an event log), (b) conformance checking (comparing the observed behavior in the event log with the modeled behavior), and (c) model enhancement (extending models based on additional information in the event logs, e.g., to highlight bottlenecks). Existing process mining techniques mainly use procedural process modeling languages for describing the business processes under examination. However, these languages are suitable to be used in stable environment where process executions are highly predictable. In turbulent environments, where process executions involve multiple alternatives, process models tend to be complex and difficult to understand. In this talk, we introduce a new family of process mining techniques based on declarative languages. These techniques are very suitable to be used for analyzing less structured business processes working in environments where high flexibility is required. These techniques have been implemented in the process mining tool ProM and range from process discovery to models repair and extension, to offline and online conformance checking.

#### Jürmo Mehine: Unifying NoSQL Data Stores

Abstract: The so-called NoSQL movement is driven largely by the need for clustered deployment of applications in cloud computing environments. Because the relational model does not lend itself easily to horizontal scaling, a number of key-value based aggregate oriented data stores have recently been developed to rise to the challenge.

Currently the space of NoSQL solutions is heterogenous with no standardization between different data stores. However examining the capabilities of different NoSQL stores reveals a pattern common to all of them. This pattern, based on the "get", "put" and "delete" operations common to all data stores, allows for the introduction of a unifying layer of abstraction for different key-value based data stores. We propose and outline the details of a software framework implementing this abstraction. As an adapter to different data sources this framework would simplify the work of application developers programming against different back end interfaces.

#### Jaak Randmets: SecreC for Sharemind 3

Slides of the talk: [pdf]

Abstract: SecreC is a high-level imperative programming language for implementing privacy-preserving applications in Sharemind framework. The third version of Sharemind supports multiple privacy-preserving computation schemes and concurrent use of them. The new version of SecreC facilitates this functionality via protection domain polymorphic functions. In this talk, we present and justify design of the new version of SecreC and present a brief overview of formalizations that helped guide the design and implementation of the language.

#### Ago-Erik Riet: On some simple additive combinatorics

Abstract: Additive combinatorics is hard to define, as Ben Green admits in his book review to "Additive Combinatorics" (2006) by Terence Tao and Van Vu. Here we shall be considering a simple problem concerning sum sets of natural numbers, without the need to go into the quite advanced machinery developed to tackle more complicated additive combinatorics problems. In the paper I will be concentrating on, we came up with our results by computer experimentation - telling us what could and needed to be proved.

Motivated by a question of Sarközy, we investigate (in a 2009 paper by Benevides, Hulgan, Lemons, Palmer, myself and Wheeler) sufficient conditions for existence of (infinite) sets of natural numbers $A$ and $B$ such that the number of solutions of the equation $a+b = n$ where $a \in A$ and $b \in B$ is monotone increasing in $n$. We also examine a generalized notion of Sidon sets. That is, we examine sets $A$, $B$ with the property that, for every $n \ge 0$, the equation above has at most one solution, i.e., all pairwise sums are distinct. We shall characterize such pairs of sets where, in addition to this Sidon property, $A+B$ (defined as $\{a+b | a\in A, b\in B \}$) is an interval of integers.

In the open problems / work in progress section the buzz word will be hypergraph, in addition to sum set and Sidon set. The part on hypergraphs is very much recent and raw ideas.

#### Vitali Skachek: Coding Theory: From the Past to the Present

Slides of the talk: [pdf]

Abstract: In this survey talk we discuss the main milestones in the development of the modern coding theory. We start with the celebrated Shannon Channel Coding Theorem, and the related motivation for development of good practical codes. We then present some important steps in the development of coding theory, including Reed-Solomon codes, their list-decoding and application to secret-sharing in cryptography, turbo codes and low-density parity-check codes. Finally, we will talk about new applications of coding theory in flash memories, network communications, gossip algorithms, distributed storage and biology.

#### Boris Šelajev: Program Verification in Spec#

Slides of the talk: [pdf]

Demo code: [SelectionSort.ssc]

Abstract: Spec# as a programming language is an extension for C# with non-null types, code contracts and object invariants. Using program specifications developer defines what he means about the program correctness and the verification tool can check consistency between specification and the program. In the talk I will explain contracts usage and show examples. The language and the tool is developed in MSR.

#### Tarmo Uustalu: Coinductive big-step semantics for concurrency

Slides of the talk: [pdf]

Abstract: In a paper presented at SOS 2010, we developed a framework for big-step semantics for interactive input-output in combination with divergence, based on coinductive and mixed inductive-coinductive notions of resumptions, evaluation and termination-sensitive weak bisimilarity. In contrast to standard inductively defined big-step semantics, this framework handles divergence properly; in particular, runs that produce some observable effects and then diverge, are not lost''. Here we scale this approach for shared-variable concurrency on a simple example language. We develop the metatheory of this semantics in a constructive logic.

#### Niccolò Veltri: A Formalization of the Max-flow Min-cut Theorem in Higher Order Logic

Slides of the talk: [pdf]

Abstract: We present a formalization of the Max-flow Min-cut theorem in HOL Light. The Max-flow Min-cut theorem is a major result in graph theory and an application of the strong duality theorem in linear programming. We formalize a graph-theoretical version of the proof of this theorem. The formalization is nontrivial not only for the complexity of this mathematical proof per se, but also because of the lack of a basic library for graphs in the standard repositories of HOL Light.

#### Vesal Vojdani: Side-effecting constraint systems: A Swiss army knife for program analysis

Abstract: Side-effecting constraint systems were originally introduced by Seidl, Vene, and Müller-Olm for the analysis of multi-threaded code. In this talk, I present our recent generalization of this idea to a unified framework for interprocedural program analysis. Side-effecting constraints allow us tweak the amount of context-sensitivity and combine context-sensitive analyses of local properties with flow-insensitive analyses of global properties. Side-effecting constraint systems thus form the ideal basis for building general-purpose infrastructures for static analysis. They constitute the core of the analyzer generator Goblint, which we used to practically evaluate this approach on real-world examples. (Joint work with Kalmer Apinis and Helmut Seidl; APLAS 2012.)

#### Jan Willemson: Secure subset cover computation via a genetic algorithm

Abstract: In this talk we introduce the secure subset covering problem, state it as a binary integer linear programming task and design a genetic algorithm to solve it. The algorithm has been implemented and benchmarked on Sharemind multi-party computation engine. We will discuss both the implementation details and benchmarking results.

#### Abuzer Yakaryilmaz: Quantum alternation

Abstract: We introduce the concept of quantum alternation as a generalization of quantum nondeterminism. We define the first quantum alternating Turing machine (qATM) by augmenting alternating Turing machine (ATM) with a fixed-size quantum register. We focus on space-bounded computation, and obtain the following surprising result: One-way qATMs with constant-space (one-way alternating quantum finite automata (1AQFA)) are Turing-equivalent. Then, we introduce strong version of qATM: The qATM that must halt in every computation path. We show that strong qATMs (similar to private ATMs) can simulate deterministic space with exponentially less space. This leads to shifting the deterministic space hierarchy exactly by one-level. We also focus on realtime versions of one-way AQFAs (rtAQFA) and then obtain many interesting results: (i) any language recognized by a rtAQFA is in quadratic deterministic space, (ii) two-alternation is better than one-alternation, (iii) two-alternation is sufficient to recognize a NP-complete language and so any language in NP can be recognized by a poly-time log-space qATM with two alternations, (iv) there-alternation is sufficient to recognize a language which is complete for second level polynomial hierarchy and so any language in the second level of polynomial hierarchy can be recognized by a poly-time log-space qATM with three alternations.

Liina Kamm
Peeter Laud
Helger Lipmaa
Tarmo Uustalu
Varmo Vene
Viimane uuendus 6.02.2013