改进的多模式匹配算法

在有限自动机的多模式匹配算法（DFSA算法）的基础上，结合Quick Search算法的优点，提出了一个快速的多模式字符串匹配算法，之后在算法中以连续跳跃的思想，给出了另一个更加有效的改进，在一般情况下，这两个算法不需要匹配目标文本串中的每个字符，并充分利用了匹配过程是本次匹配不成功的信息，跳过尽可能多的字符，在模式串较长和较短的情况下，算法都有很好的性能，实验表明，在模式串较短时，所提出的算法需要的匹配时间仅为DFSA算法的1／2到1／5，在模式串较长时，所需时间为DFSA算法的1／3至1／7。     

一种基于反向有限自动机的多模式匹配算法

在基于有限自动机的多模式匹配算法DFSA的基础上,结合改进的BM单模式匹配算法的优点,提出一种快速的多模式字符串匹配算法。在一般情况下,该算法不需要匹配目标文本串的每个字符,能充分利用匹配过程中本次匹配不成功的信息和已成功的信息,跳过尽可能多的字符。实验表明,模式串较短时,该算法需要的时间约为DFSA的1/2,模式串较长时,所需时间约为DFSA算法的1/3。     

改进的多模式字符串匹配算法

在经典的AC多模式字符串匹配算法的基础上，结合BMH算法的优点，提出了一种快速的多模式字符串匹配算法。一般情况下，该算法不需要匹配目标文本串中的每个字符，而是在实际比较之前跳过尽可能多的字符，以减少字符比较的操作，实现快速匹配。在模式串较长和较短的情况下，算法都有很好的性能。实验表明，在模式串较短时，本算法所需的时间仅为AC算法的50%～30%；在模式串较长时，所需时间为AC算法的26.7%～15.2%。     

An efficient algorithm for matching multiple patterns

An efficient algorithm for performing multiple pattern match in a string is described. The match algorithm combines the concept of deterministic finite state automata (DFSA) and the Boyer-Moore algorithm to achieve better performance. Experimental results indicate that in the average case, the algorithm is able to perform pattern match operations sublinearly, i.e. it does not need to inspect every character of the string to perform pattern match operations. The analysis shows that the number of characters to be inspected decreases as the length of patterns increases, and increases slightly as the total number of patterns increases. To match an eight-character pattern in an English string using the algorithm, only about 17% of all characters of the strong and 33% of all characters of the string, when the number of patterns is seven, are inspected. In an actual testing, the algorithm running on SUN 3/160 takes only 3.7 s to search seven eight-character patterns in a 1.4-Mbyte English text file     

一种快速的基于BM模式匹配的改进算法

模式匹配算法是入侵检测系统(IDS) 中非常重要的一种算法. 在研究和分析几种常用模式匹配算法的基础 上, 提出一种快速的基于BM(Boyer-Moore) 模式匹配的改进算法—–IBM 算法. 该算法充分利用模式串的末字符和 末字符所对应的文本串的后两字符的唯一性, 同时参考文本串本身的信息来提高模式串的移动量, 使得每次失配后, 在保证不丢失匹配成功可能性的前提下尽可能多地向后跳跃. 实验结果表明, 该算法相比其他模式匹配算法, 在检测 性能和匹配效率上均具有很大优势, 并且能够有效地提高IDS 的检测效率和性能.

     

The design of efficient algorithms for two-dimensional patternmatching

The two-dimensional pattern matching problem finds the occurrences of a given two-dimensional pattern array in a two-dimensional text array. The paper presents two efficient algorithms, which combine Fan-Su (1993) and Aho-Corasick (1979) string search algorithms, to solve this problem. The proposed algorithms need not inspect each character of the text array during the pattern matching in most cases. Additionally, unlike the algorithms proposed by Zhu and Takaoka (1989) which are based on the hashing method, these new algorithms require no preprocessing of the text array. A comparison of the performance of various algorithms is presented. The result shows that the proposed algorithms are about three to six times faster than the best algorithm proposed previously when the size of the pattern array is less than 1/100 of the size of the text array, which occurs frequently in many applications     

Word searching in unconstrained layout using character pair coding

Word searching in non-structural layout such as graphical documents is a difficult task due to arbitrary orientations of text words and the presence of graphical symbols. This paper presents an efficient approach for word searching in documents of non-structural layout using an efficient indexing and retrieval approach. The proposed indexing scheme stores spatial information of text characters of a document using a character spatial feature table (CSFT). The spatial feature of text component is derived from the neighbor component information. The character labeling of a multi-scaled and multi-oriented component is performed using support vector machines. For searching purpose, the positional information of characters is obtained from the query string by splitting it into possible combinations of character pairs. Each of these character pairs searches the position of corresponding text in document with the help of CSFT. Next, the searched text components are joined and formed into sequence by spatial information matching. String matching algorithm is performed to match the query word with the character pair sequence in documents. The experimental results are presented on two different datasets of graphical documents: maps dataset and seal/logo image dataset. The results show that the method is efficient to search query word from unconstrained document layouts of arbitrary orientation.     

LZgrep: a Boyer–Moore string matching tool for Ziv–Lempel compressed text

We present a Boyer–Moore (BM) approach to string matching over LZ78 and LZW compressed text. The idea is to search the text directly in compressed form instead of decompressing and then searching it. We modify the BM approach so as to skip text using the characters explicitly represented in the LZ78/LZW formats, modifying the basic technique where the algorithm can choose which characters to inspect. We present and compare several solutions for single and multipattern searches. We show that our algorithms obtain speedups of up to 50% compared to the simple decompress‐then‐search approach. Finally, we present a public tool, LZgrep, which uses our algorithms to offer grep‐like capabilities directly searching files compressed using Unix's Compress, a LZW compressor. LZgrep can also search files compressed with Unix gzip, using new decompress‐then‐search techniques we develop, which are faster than the current tools. This way, users can always keep their files in compressed form and still search them, uncompressing only when they want to see them. Copyright © 2005 John Wiley & Sons, Ltd.     

Improving an Algorithm for Approximate Pattern Matching

We study a recent algorithm for fast on-line approximate string matching. This is the problem of searching a pattern in a text allowing errors in the pattern or in the text. The algorithm is based on a very fast kernel which is able to search short patterns using a nondeterministic finite automaton, which is simulated using bit-parallelism. A number of techniques to extend this kernel for longer patterns are presented in that work. However, the techniques can be integrated in many ways and the optimal interplay among them is by no means obvious. The solution to this problem starts at a very low level, by obtaining basic probabilistic information about the problem which was not previously known, and ends integrating analytical results with empirical data to obtain the optimal heuristic. The conclusions obtained via analysis are experimentally confirmed. We also improve many of the techniques and obtain a combined heuristic which is faster than the original work. This work shows an excellent example of a complex and theoretical analysis of algorithms used for design and for practical algorithm engineering, instead of the common practice of first designing an algorithm and then analyzing it. Received March 31, 1998; revised November 18, 1998.     

一种改进的字符串模式匹配算法

提出一种改进的字符串模式匹配算法。该算法对文本串进行预处理,即对文本串中不存在于模式串中的字符以及文本串中剩下的出现次数最少的字符分别进行标记,再通过匹配模式串的首尾字符来减少出现次数最少的字符的标记个数。发生匹配失败时,将模式串直接滑动到标记了的出现次数最少的字符处。通过实验证明,该算法的移动次数和比较次数有较大减少,耗费的额外空间的大小也不超过模式串的长度,进一步提高模式匹配的效率。     

一种基于分段匹配的字符串匹配算法

针对已有算法对文本和模式的相关性依赖较大,提出一种基于分段的字符串匹配算法——SM。该算法利用特殊字符将文本先分段再匹配,且匹配过程对模式内容和长度不敏感。通过将SM算法与经典算法进行分析和实验对比,证明SM算法性能稳定,特别是在多模式字符串匹配情况下,SM算法具有比Wu-Manber算法更快的速度和更小的空间消耗。     

Access concentration detection in click logs to improve mobile Web-IR

Effective ranking algorithms for mobile Web searches are being actively pursued. Due to the peculiar and troublesome properties of mobile contents such as scant text, few outward links, and few input keywords, conventional Web search techniques using bag-of-words ranking functions or link-based algorithms are not good enough for mobile Web searches. Our solution is to use click logs to clarify access-concentrated search results for each query and to utilize the titles and snippets to expand the queries. Many previous works regard the absolute click numbers as the degree of access concentration, but they are strongly biased such that higher-ranked search results are more easily clicked than lower-ranked ones. Therefore, it is considered that only higher-ranked search results are access-concentrated ones and that only terms extracted from them can be used to expand a query. In this paper, we introduce a new measure that is capable of estimating the degree of access concentration. This measure is used to precisely extract access concentration sites from many search results and to expand queries with terms extracted from them. We conducted an experiment using the click logs and data from an actual mobile Web search site. Results obtained show that our proposed method is a more effective way to boost the search precision than using other query expansion methods such as the top K search results or the most-often-clicked search results.     

基于过滤的中文多模式近似字符串匹配算法

当前近似字符串匹配算法主要针对英文等中小字符集，该文针对汉字等大字符集的有效算法很少，尤其缺少适合汉字等大字符集的多模式近似匹配算法的情况，提出了一种适合汉字等大字符集的多模式近似匹配算法——MBPM-BM，通过实验证明了该算法的有效性。 近似字符串匹配；中文字符串匹配；多模式匹配；位并行运算；过滤     

The suffix-signature method for searching for phrases in text

We present a new algorithm to find all occurrences of a given phrase based on the data structure known as a suffix array and using a corresponding array of signatures. With this algorithm, matches to phrases of moderate length can be found with expected search time of one disk access to the text and one disk access to its index. To achieve this performance for phrases of up to five words in length requires an index having total size of approximately 120% of the size of the text. The algorithm guarantees a worst case search performance of two disk accesses to the text per phrase search. Experiments with actual data ranging in size from 6Mb to 550Mb and with actual query patterns derived from logs of searches on the World Wide Web show that the approach is applicable in practice to a variety of texts and realistic phrase searches.     

A robust model for on-line handwritten japanese text recognition

This paper describes a robust context integration model for on-line handwritten Japanese text recognition. Based on string class probability approximation, the proposed method evaluates the likelihood of candidate segmentation–recognition paths by combining the scores of character recognition, unary and binary geometric features, as well as linguistic context. The path evaluation criterion can flexibly combine the scores of various contexts and is insensitive to the variability in path length, and so, the optimal segmentation path with its string class can be effectively found by Viterbi search. Moreover, the model parameters are estimated by the genetic algorithm so as to optimize the holistic string recognition performance. In experiments on horizontal text lines extracted from the TUAT Kondate database, the proposed method achieves the segmentation rate of 0.9934 that corresponds to a f-measure and the character recognition rate of 92.80%.     

Sampled suffix array with minimizers

Sampling (evenly) the suffixes from the suffix array is an old idea trading the pattern search time for reduced index space. A few years ago Claude et al. showed an alphabet sampling scheme allowing for more efficient pattern searches compared with the sparse suffix array, for long enough patterns. A drawback of their approach is the requirement that sought patterns need to contain at least one character from the chosen subalphabet. In this work, we propose an alternative suffix sampling approach with only a minimum pattern length as a requirement, which is more convenient in practice. Experiments show that our algorithm (in a few variants) achieves competitive time‐space tradeoffs on most standard benchmark data. Copyright © 2017 John Wiley & Sons, Ltd.     

一种改进的BM字符串匹配算法

经典字符串匹配算法的本质都是从左向右或者从右向左顺序进行字符匹配的,在主串中存在大量子串与模式串前缀或者后缀相同时效率较低,并且模式串最大右移长度为模式串长度。改进算法采用二分匹配字符串的方法,有效地避免了由主串中大量子串与模式串前缀相同或者后缀相同引起的无意义比较次数。模式串的移动距离根据改进的坏字符规则进行计算,增大了模式串的移动距离。实验结果表明,改进的字符串匹配算法可以有效地减少字符串的匹配次数和移动次数,达到了提高算法效率的目的。     

Computing Longest Previous non-overlapping Factors

The Longest Previous non-overlapping Factor table (LPnF) stores for each position of a string the maximal length of factors occurring both there and in the preceding part of the string. The notion is a slight variant of the LPF table described before and used for text compression. The LPnF table is an essential element for the design of efficient algorithms on strings as it is related to a certain type of Ziv-Lempel factorisation used for this purpose.We show how to compute the LPnF table in linear time from the suffix array of the string when it is drawn from an integer alphabet. The algorithm is a non-immediate extension of the LPF computation and it does not require any other sophisticated data structure than the suffix array of the input string.     

On-line string matching algorithms: survey and experimental results

In this paper we present a short survey and experimental results for well known sequential string matching algorithms. We consider algorithms based on different approaches including classical, suffix automata, bit-parallelism and hashing. We put special emphasis on algorithms recently presented such as Shift-Or and BNDM algorithms. We compare these algorithms in terms of the number of character comparisons and the running time for four different types of text: binary alphabet, alphabet of size 8, English alphabet and DNA alphabet.