String (computer science)

About: String (computer science) is a research topic. Over the lifetime, 19430 publications have been published within this topic receiving 333247 citations. The topic is also known as: str & s.

Uniform Random Generation of Strings in a Context-Free Language

Abstract: Let S be the set of all strings of length n generated by a given context-free grammar. A uniform random generator is one which produces strings from S with equal probability. In generating these strings, care must be taken in choosing the disjuncts that form the right-hand side of a grammar rule so that the produced string will have the specified length. Uniform random generators have applications in studying the complexity of parsers, in estimating the average efficiency of theorem provers for the propositional calculus, in establishing a measure of ambiguity of a grammar, etc. Two methods are presented for generating uniform random strings in an unambiguous context-free language. The first method will generate a random string of length n in linear time, but must use a precomputed table of size $O(n^{r + 1} )$, where r is the number of nonterminals in the grammar used to specify the language. The second method precomputes part of the table and calculates the other entries as they are called for. It requi...

Top-k string similarity search with edit-distance constraints

Abstract: String similarity search is a fundamental operation in many areas, such as data cleaning, information retrieval, and bioinformatics. In this paper we study the problem of top-k string similarity search with edit-distance constraints, which, given a collection of strings and a query string, returns the top-k strings with the smallest edit distances to the query string. Existing methods usually try different edit-distance thresholds and select an appropriate threshold to find top-k answers. However it is rather expensive to select an appropriate threshold. To address this problem, we propose a progressive framework by improving the traditional dynamic-programming algorithm to compute edit distance. We prune unnecessary entries in the dynamic-programming matrix and only compute those pivotal entries. We extend our techniques to support top-k similarity search. We develop a range-based method by grouping the pivotal entries to avoid duplicated computations. Experimental results show that our method achieves high performance, and significantly outperforms state-of-the-art approaches on real-world datasets.

Experimental results on string matching algorithms

Abstract: We present experimental results for string matching algorithms which are known to be fast in practice. We compare these algorithms through two aspects : the number of text character inspections and the running time. These experiments show that for large alphabets and small patterns the Quick Search algorithm of Sunday is the most efficient and that for small alphabets and large patterns it is the Reverse Factor algorithm of Crochemore et al. which is the most efficient.

Nonlinear Regression With Linear Constraints: An Extension of the Magnified Diagonal Method

Abstract: A syntax-directed picture analysis system based on a formal picture description scheme is described. The system accepts a description of a set of pictures in terms of a grammar generating strings in a picture description language; the grammar is explicitly used to direct the analysis or parse, and to control the calls on pattern classification routines for primitive picture components. Pictures are represented by directed graphs with labeled edges, where the edges denote elementary picture components and the graph connectivity mirrors the picture component connectivity; blank and don't care “patterns” allow the description of simple relations between visible patterns. The bulk of the paper is concerned with the picture parsing algorithm which is an n-dimensional analog of a classical top-down string parser, and an application of an implemented system to the analysis of spark chamber film. The potential benefits of this approach, as demonstrated by the application, include ease of implementation and modification of picture processing systems, and simplification of the pattern recognition problem by automatically taking advantage of contextual information.

String of beads

Abstract: A string of beads with deformable connecting pieces ( 2 ) that extend between each pair of adjacent beads ( 1 ) and are secured to the beads ( 1 ), wherein the connecting pieces ( 2 ) are plastics threads or flexible wires.