arXiv subjects

Mitja Kulczynski

Publications and source records attributed to Mitja Kulczynski.

8 recordsLinked to original sources

arXiv2022

A Generic Information Extraction System for String Constraints

String constraint solving, and the underlying theory of word equations, are highly interesting research topics both for practitioners and theoreticians working in the wide area of satisfiability modulo theories. As string constraint solving algorithms, a.k.a. string solvers, gained a more prominent role in the formal analysis of string-heavy programs, especially in connection to symbolic code execution and security protocol verification, we can witness an ever-growing number of benchmarks collecting string solving instances from real-world applications as well as an ever-growing need for more efficient and reliable solvers, especially for the aforementioned real-world instances. Thus, it seems that the string solving area (and the developers, theoreticians, and end-users active in it) could greatly benefit from a better understanding and processing of the existing string solving benchmarks. In this context, we propose SMTQUERY: an SMT-LIB benchmark analysis tool for string constraints. SMTQUERY is implemented in Python 3, and offers a collection of analysis and information extraction tools for a comprehensive data base of string benchmarks (presented in SMT-LIB format), based on an SQL-centred language called QLANG.

cs.LO↗

arXiv2021

Analysis of Source Code Using UPPAAL

In recent years there has been a considerable effort in optimising formal methods for application to code. This has been driven by tools such as CPAChecker, DIVINE, and CBMC. At the same time tools such as Uppaal have been massively expanding the realm of more traditional model checking technologies to include strategy synthesis algorithms - an aspect becoming more and more needed as software becomes increasingly parallel. Instead of reimplementing the advances made by Uppaal in this area, we suggest in this paper to develop a bridge between the source code and the engine of Uppaal. Our approach uses the widespread intermediate language LLVM and makes recent advances of the Uppaal ecosystem readily available to analysis of source code.

cs.SE↗

arXiv2021

The Show Must Go On -- Examination During a Pandemic

When unexpected incidents occur, new innovative and flexible solutions are required. If this event is something such radical and dramatic like the COVID-19 pandemic, these solutions must aim to guarantee as much normality as possible while protecting lives. After a moment of shock our university decided that the students have to be able to pursue their studies for guaranteeing a degree in the expected time since most of them faced immediate financial problems due to the loss of their student jobs. This implied, for us as teachers, that we had to reorganise not only the teaching methods from nearly one day to the next, but we also had to come up with an adjusted way of examinations which had to take place in person with pen and paper under strict hygiene rules. On the other hand the correction should avoid personal contacts. We developed a framework which allowed us to correct the digitalised exams safely at home while providing the high standards given by the general data protection regulation of our country. Moreover, the time spent in the offices could be reduced to a minimum thanks to automatically generated exam sheets, automatically re-digitalised and sorted worked-on exams.

cs.CY↗

arXiv2021

String Theories involving Regular Membership Predicates: From Practice to Theory and Back

Widespread use of string solvers in formal analysis of string-heavy programs has led to a growing demand for more efficient and reliable techniques which can be applied in this context, especially for real-world cases. Designing an algorithm for the (generally undecidable) satisfiability problem for systems of string constraints requires a thorough understanding of the structure of constraints present in the targeted cases. In this paper, we investigate benchmarks presented in the literature containing regular expression membership predicates, extract different first order logic theories, and prove their decidability, resp. undecidability. Notably, the most common theories in real-world benchmarks are PSPACE-complete and directly lead to the implementation of a more efficient algorithm to solving string constraints.

cs.CL↗

arXiv2021

An SMT Solver for Regular Expressions and Linear Arithmetic over String Length

We present a novel length-aware solving algorithm for the quantifier-free first-order theory over regex membership predicate and linear arithmetic over string length. We implement and evaluate this algorithm and related heuristics in the Z3 theorem prover. A crucial insight that underpins our algorithm is that real-world instances contain a wealth of information about upper and lower bounds on lengths of strings under constraints, and such information can be used very effectively to simplify operations on automata representing regular expressions. Additionally, we present a number of novel general heuristics, such as the prefix/suffix method, that can be used in conjunction with a variety of regex solving algorithms, making them more efficient. We showcase the power of our algorithm and heuristics via an extensive empirical evaluation over a large and diverse benchmark of 57256 regex-heavy instances, almost 75% of which are derived from industrial applications or contributed by other solver developers. Our solver outperforms five other state-of-the-art string solvers, namely, CVC4, OSTRICH, Z3seq, Z3str3, and Z3-Trau, over this benchmark, in particular achieving a 2.4x speedup over CVC4, 4.4x speedup over Z3seq, 6.4x speedup over Z3-Trau, 9.1x speedup over Z3str3, and 13x speedup over OSTRICH.

cs.LO↗

arXiv2021

Weighted Prefix Normal Words: Mind the Gap

A prefix normal word is a binary word whose prefixes contain at least as many 1s as any of its factors of the same length. Introduced by Fici and Lipták in 2011 the notion of prefix normality is so far only defined for words over the binary alphabet. In this work we investigate a generalisation for finite words over arbitrary finite alphabets, namely weighted prefix normality. We prove that weighted prefix normality is more expressive than binary prefix normality. Furthermore, we investigate the existence of a weighted prefix normal form since weighted prefix normality comes with several new peculiarities that did not already occur in the binary case. We characterise these issues and finally present a standard technique to obtain a generalised prefix normal form for all words overarbitrary, finite alphabets.

cs.FL↗

arXiv2020

On Collapsing Prefix Normal Words

Prefix normal words are binary words in which each prefix has at least the same number of $\so$s as any factor of the same length. Firstly introduced by Fici and Lipták in 2011, the problem of determining the index of the prefix equivalence relation is still open. In this paper, we investigate two aspects of the problem, namely prefix normal palindromes and so-called collapsing words (extending the notion of critical words). We prove characterizations for both the palindromes and the collapsing words and show their connection. Based on this, we show that still open problems regarding prefix normal words can be split into certain subproblems.

cs.FL↗

arXiv2019

On Solving Word Equations Using SAT

We present Woorpje, a string solver for bounded word equations (i.e., equations where the length of each variable is upper bounded by a given integer). Our algorithm works by reformulating the satisfiability of bounded word equations as a reachability problem for nondeterministic finite automata, and then carefully encoding this as a propositional satisfiability problem, which we then solve using the well-known Glucose SAT-solver. This approach has the advantage of allowing for the natural inclusion of additional linear length constraints. Our solver obtains reliable and competitive results and, remarkably, discovered several cases where state-of-the-art solvers exhibit a faulty behaviour.

cs.FL↗