Class Of Regular Expressions Research Articles

Regular Expression Matching using Bit Vector Automata

Regular expressions (regexes) are ubiquitous in modern software. There is a variety of implementation techniques for regex matching, which can be roughly categorized as (1) relying on backtracking search, or (2) being based on finite-state automata. The implementations that use backtracking are often chosen due to their ability to support advanced pattern-matching constructs. Unfortunately, they are known to suffer from severe performance problems. For some regular expressions, the running time for matching can be exponential in the size of the input text. In order to provide stronger guarantees of matching efficiency, automata-based regex matching is the preferred choice. However, even these regex engines may exhibit severe performance degradation for some patterns. The main reason for this is that regexes used in practice are not exclusively built from the classical regular constructs, i.e., concatenation, nondeterministic choice and Kleene's star. They involve additional constructs that provide succinctness and convenience of expression. The most common such construct is bounded repetition (also called counting), which describes the repetition of the pattern a fixed number of times. In this paper, we propose a new algorithm for the efficient matching of regular expressions that involve bounded repetition. Our algorithms are based on a new model of automata, which we call nondeterministic bit vector automata (NBVA). This model is chosen to be expressively equivalent to nondeterministic counter automata with bounded counters, a very natural model for expressing patterns with bounded repetition. We show that there is a class of regular expressions with bounded repetition that can be matched in time that is independent from the repetition bounds. Our algorithms are general enough to cover the vast majority of challenging bounded repetitions that arise in practice. We provide an implementation of our approach in a regex engine, which we call BVA-Scan. We compare BVA-Scan against state-of-the-art regex engines on several real datasets.

Linear Time Membership in a Class of Regular Expressions with Counting, Interleaving, and Unordered Concatenation

Regular Expressions (REs) are ubiquitous in database and programming languages. While many applications make use of REs extended with interleaving ( shuffle ) and unordered concatenation operators, this extension badly affects the complexity of basic operations, and, especially, makes membership NP-hard, which is unacceptable in most practical scenarios. In this article, we study the problem of membership checking for a restricted class of these extended REs, called conflict-free REs , which are expressive enough to cover the vast majority of real-world applications. We present several polynomial algorithms for membership checking over conflict-free REs. The algorithms are all polynomial and differ in terms of adopted optimization techniques and in the kind of supported operators. As a particular application, we generalize the approach to check membership of Extensible Markup Language trees into a class of EDTDs (Extended Document Type Definitions) that models the crucial aspects of DTDs (Document Type Definitions) and XSD (XML Schema Definitions) schemas. Results about an extensive experimental analysis validate the efficiency of the presented membership checking techniques.

A lightweight regular model checking approach for parameterized systems

In recent years, we have designed a lightweight approach to regular model checking specifically designed for parameterized systems with global conditions. Our approach combines the strength of regular languages, used for representing infinite sets of configurations, with symbolic model checking and approximations. In this paper, we give a uniform presentation of several variations of a symbolic backward reachability scheme in which different classes of regular expressions are used in place of BDDs. The classification of the proposed methods is based on the precision of the resulting approximated analysis.

XML data exchange

Data exchange is the problem of finding an instance of a target schema, given an instance of a source schema and a specification of the relationship between the source and the target. Theoretical foundations of data exchange have recently been investigated for relational data. In this article, we start looking into the basic properties of XML data exchange, that is, restructuring of XML documents that conform to a source DTD under a target DTD, and answering queries written over the target schema. We define XML data exchange settings in which source-to-target dependencies refer to the hierarchical structure of the data. Combining DTDs and dependencies makes some XML data exchange settings inconsistent. We investigate the consistency problem and determine its exact complexity. We then move to query answering, and prove a dichotomy theorem that classifies data exchange settings into those over which query answering is tractable, and those over which it is coNP-complete, depending on classes of regular expressions used in DTDs. Furthermore, for all tractable cases we give polynomial-time algorithms that compute target XML documents over which queries can be answered.

On a generalization of regular expression

CF expressions are defined. Using the concept of D-graphs, it is demonstrated that CF expressions define CF languages. A subclass (equivalent to the class of regular expressions) of pseudo-coiterating CF expressions is defined.

Efficient expansion of factored expressions

Regular expressions and the languages they represent have a wide range of applications in computing. We consider a special class of regular expressions. A factored expression is a regular expression with no closure symbols.

Sequential Circuit Output Probabilities From Regular Expressions

This paper presents a number of methods for finding sequential circuit output probabilities using regular expressions. Various classes of regular expressions, based on their form, are defined and it is shown how to easily find multistep transition probabilities directly from the regular expressions. A new procedure for finding steady-state probabilities is given which proceeds either from a regular expression or a state diagram description. This procedure is based on the concept of synchronization of the related machine, and is useful for those problems where synchronization sequences exist. In the cases where these techniques can be utilized, substantial savings in computation can be realized. Furthermore, application to other areas such as multinomial Markov processes is immediate.

Symmetric and Antisymmetric Regular Expressions

In this paper the “dual” of a binary regular expression is defined as the same expression with 0’s and 1’s interchanged. The “duals” of tapes and events are defined analogously, and various properties and interrelations associated with duality are developed. On the basis of these definitions, two classes of regular expressions are introduced—the “symmetric” and the “antisymmetric” regular expressions (these classes are shown to be infinite). A symmetric expression is one whose dual represents the same event, while an antisymmetric expression is one whose dual represents the complement of the same event. Thus, the acceptor of an event represented by a symmetric expression is invariant under input complementation, while the acceptor of an event represented by an antisymmetric expression is invariant under simultaneous complementation of input and output. It is shown that the class of symmetric expressions is closed under regular operations, while the class of antisymmetric expressions is closed only under s...