http://liacs.leidenuniv.nl/~stefanovtp/courses/StudentenSeminarium/Papers/FI2/AXML.pdf

Automata for XML---A survey

In this paper we investigate the problem of validating, with constant memory, streaming XML documents with respect to a DTD. Such constant memory validations can only be performed for some but not all DTDs. This paper gives a non trivial interesting step towards characterizing those DTDs for which a constant-memory on-line algorithm exists.

/pdf/constant-memory-validation-of-streaming-xml-documents-47wexbtxe6.pdf

Constant-memory validation of streaming XML documents against DTDs

We investigate the decidability and complexity of various model checking problems over one-counter automata. More specifically, we consider succinct one-counter automata, in which additive updates are encoded in binary, as well as parametric one-counter automata, in which additive updates may be given as unspecified parameters. We fully determine the complexity of model checking these automata against CTL, LTL, and modal µ-calculus specifications.

/pdf/model-checking-succinct-and-parametric-one-counter-automata-znigc2q0yx.pdf

Model checking succinct and parametric one-counter automata

We study decidability and complexity issues for fragments of LTL with Presburger constraints by restricting the syntactic resources of the formulae (the class of constraints, the number of variables and the distance between two states for which counters can be compared) while preserving the strength of the logical operators. We provide a complete picture refining known results from the literature, in some cases pushing forward the known decidability limits. By way of example, we show that model-checking formulae from LTL with quantifier-free Presburger arithmetic over one-counter automata is only PSPACE-complete. In order to establish the PSPACE upper bound, we show that the nonemptiness problem for Buchi one-counter automata taking values in Z and allowing zero tests and sign tests, is only NLOGSPACE-complete.

/pdf/the-effects-of-bounding-syntactic-resources-on-presburger-1dsfq3rgv0.pdf

The Effects of Bounding Syntactic Resources on Presburger LTL

Theoretical and practical aspects of the verification of infinite-state systems have attracted a lot of interest in the verification community throughout the last 30 years. One goal is to identify classes of infinite-state systems that admit decidable decision problems on the one hand, and which are sufficiently general to model systems, programs or protocols with unbounded data or recursion depth on the other hand. The first part of this thesis is concerned with the computational complexity of verifying counter automata, which are a fundamental and widely studied class of infinite-state systems. Counter automata consist of a finite-state controller manipulating a finite number of counters ranging over the naturals. A classic result by Minsky states that reachability in counter automata is undecidable already for two counters. One restriction that makes reachability decidable and that this thesis primarily focuses on is the restriction to one counter. A main result of this thesis is to show that reachability in one-counter automata with counter updates encoded in binary is NP-complete, which solves a problem left open by Rosier and Yen in 1986. We also consider parametric one-counter automata, in which counter updates can be parameters ranging over the naturals. Reachability for this class asks whether there are values of the parameters such that a target configuration can be reached from an initial configuration. This problem is also shown to be NP-complete. Subsequently, we establish decidability and complexity results of model checking problems for one-counter automata with and without parameters for specifications written in EF, CTL and LTL. The second part of this thesis is about the verification of programs with pointers and linked lists in the framework of separation logic. We consider the fragment of separation logic introduced by Berdine, Calcagno and O'Hearn in 2004 and the problem of deciding entailment between formulae of this fragment. We improve the known coNP upper bound and show that this problem can actually be solved in polynomial time. This result is based on a novel approach in which we represent separation logic formulae as graphs and decide entailment between them by checking for the existence of a graph homomorphism. We complement this result by considering various natural extensions of this fragment which make entailment coNP-hard.

/pdf/on-the-complexity-of-model-checking-counter-automata-1bptfl8i4k.pdf

On the Complexity of Model Checking Counter Automata

We study validation of streamed XML documents by means of finite state machines. Previous work has shown that validation is in principle possible by finite state automata, but the construction was prohibitively expensive, giving an exponential-size nondeterministic automaton. Instead, we want to find deterministic automata for validating streamed documents: for them, the complexity of validation is constant per tag. We show that for a reading window of size one and nonrecursive DTDs with one-unambiguous content (i.e. conforming to the current XML standard) there is an algorithm producing a deterministic automaton that validates documents with respect to that DTD. The size of the automaton is at most exponential and we give matching lower bounds. To capture the possible advantages offered by reading windows of size k, we introduce k-unambiguity as a generalization of one-unambiguity, and study the validation against DTDs with k-unambiguous content. We also consider recursive DTDs and give conditions under which they can be validated against by using one-counter automata.

Cristiana Chitic

Papers

On validation of XML streams using finite state machines