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BIT (Copenhagen) 1985年第4期25卷 652-666页

作者： Kraaijevanger, J.F.B.M. Univ of Leiden Inst of Applied Mathematics & Computer Science Leiden Neth Univ of Leiden Inst of Applied Mathematics & Computer Science Leiden Neth

We present upper bounds for the global discretization error of the implicit midpoint rule and the trapezoidal rule for the case of arbitrary variable stepsizes. Specializing our results for the case of constant stepsi... 详细信息

关键词： MATHEMATICAL TECHNIQUES

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Cross-lingual question answering by answer translation

Cross-lingual question answering by answer translation

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2006 Cross Language Evaluation Forum Workshop, CLEF 2006, co-located with the 10th European Conference on Digital Libraries, ECDL 2006

作者： Bos, Johan Nissim, Malvina Linguistic Computing Laboratory Department of Computer Science University of Rome la Sapienza Italy Laboratory for Applied Ontology Inst. for Cognitive Science and Technology National Research Council Rome Italy

We approach cross-lingual question answering by using a mono-lingual QA system for the source language and by translating resulting answers into the target language. As far as we are aware, this is the first cross-lingual QA system in the history of CLEF that uses this method-all other cross-lingual QA systems known to us use translation of the question or query inst.ad. We demonstrate the feasibility of this approach by using a mono-lingual QA system for English, and translating answers and finding appropriate documents in Italian and Dutch. For factoid and definition questions, we achieve overall accuracy scores ranging from 13% (EN→NL) to 17% (EN→IT) and lenient accuracy figures from 19% (EN→NL) to 25% (EN→IT). The advantage of this strategy to cross-lingual QA is that translation of answers is easier than translating questions-the disadvantage is that answers might be missing from the source corpus and additional effort is required for finding supporting documents of the target language.

关键词： Natural language processing systems

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Towards weak bisimulation for coalgebras

Towards weak bisimulation for coalgebras

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Categorical Methods for Concurrency, Interaction, and Mobility (CONCUR 2002 Satellite Workshop)

作者： Rothe, Jan Mašulović, Dragan Inst. for Theor. Computer Science Dresden University of Technology D-01062 Dresden Germany Inst. of Mathematics and Informatics University of Novi Sad Trg D. Obradovića 4 21000 Novi Sad Yugoslavia

This paper contains a novel approach to observational equivalence for coalgebras. We describe how to define weak homomorphisms, weak bisimulation, and investigate the connection between them as well as the relation to the known theory of bisimulation for coalgebras. The ultimate result of the paper is the correctness-proof for a weak coinduction proof principle. ©2002 Published by Elsevier science B. V.

关键词： computer science

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A master theorem for discrete divide and conquer recurrences

A master theorem for discrete divide and conquer recurrences

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作者： Drmota, Michael Szpankowski, Wojciech Inst. Discrete Mathematics and Geometry TU Wien A-1040 Wien Austria Department of Computer Science Purdue University West Lafayette IN 47907-2066 United States

ISBN: (纸本)9780898719932

Divide-and-conquer recurrences are one of the most studied equations in computer science. Yet, discrete versions of these recurrences, namely m T(n) = an + ∑j=1m bjT([pjn + δj]) for some known sequence an and given b j, pj and δj, present some challenges. The discrete nature of this recurrence (represented by the floor function) introduces certain oscillations not captured by the traditional Master Theorem, for example due to Akra and Beizzi who primary studied the con-tinuous version of the recurrence. We apply powerful techniques such as Dirichlet series, Mellin-Perron formula, and (extended) Tauberian theorems of Wiener-Ikehara to provide a complete and precise solution to this basic computer science recurrence. We illustrate applicability of our results on several examples including a popular and fast arithmetic coding algorithm due to Boncelet for which we estimate its average redundancy. To the best of our knowledge, discrete divide and conquer recurrences were not studied in this generality and such detail;in particular, this allows us to compare the redinidancy of Boncelet's algorithm to the (asymptotically) optimal Tunstall scheme.

关键词： Data compression

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Modal logics for observation equivalences

Modal logics for observation equivalences

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CMCS'03, Coalgebraic Methods in computer science Satellite Event for ETAPS 2003)

In our paper [RM02a] we describe an approach to weak bisimulation for coalgebras and show that parts of the theory of universal coalgebra (with strong bisimulation) can be obtained when considering coalgebras with weak bisimulations and weak homomorphisms. In the present paper we focus on uniformly adapting modal logics that characterise strong bisimulation for coalgebras to several kinds of observation equivalences. ©2003 Published by Elsevier science B. V.

关键词： Formal logic

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On locally delaunay geometric graphs

On locally delaunay geometric graphs

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Proceedings of the Twentieth Annual Symposium on Computational Geometry (SCG'04)

作者： Pinchasi, Rom Smorodinsky, Shakhar Department of Mathematics Massachusetts Inst. of Technology Cambridge MA 02139 United States Math. Sciences Research Institute Berkeley CA 94720 United States Inst. for Theor. Computer Science ETH Zurich Switzerland

A geometric graph is a simple graph G = (V, E) with an embedding of the set V in the plane such that the points that represent V are in general position. A geometric graph is said to be k-locally Delaunay (or a D k-graph) if for each edge (u, v) ∈ E there is a (Euclidean) disc d that contains u and v but no other vertex of G that is within k hops from u or v. The study of these graphs was recently motivated by topology control for wireless networks. We obtain the following results: (i) We prove that if G is a Di-graph on n vertices, then it has O(n3/2) edges. (ii) We show that for any n there exist D1-graphs with n vertices and Ω(n4/3) edges. (iii) We prove that if G is a D 2-graph on n vertices, then it has O(n) edges. This bound is worst-case asymptotically tight. As an application of the first result, we show that: (iv) The maximum size of a family of pairwise non-overlapping lenses in an arrangement of n unit circles in the plane is O(n3/2). The first two results improve the best previously known upper and lower bounds of O(n 5/3) and Ω(n) respectively (see [6]). The third result improves the best previously known upper bound of O(n log n). Finally, our last result improves the best previously known upper bound (for the more general case of not necessarily unit circles) of O(n3/2k(n)) (see [1]), where k(n) = (log n)O(α2(n)) and where α(n) is the extremely slowly growing inverse Ackermann's function.

关键词： Graph theory

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TransSQL: A translation and validation-based solution for SQL-injection attacks

TransSQL: A translation and validation-based solution for SQ...

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1st International Conference on Robot, Vision and Signal Processing, RVSP 2011

作者： Zhang, Kai-Xiang Lin, Chia-Jun Chen, Shih-Jen Hwang, Yanling Huang, Hao-Lun Hsu, Fu-Hau Computer Science and Info. Engineering National Central University Chungli Taoyuan Taiwan Network and Multimedia Inst. Inst. for Info. Industry Taipei Taiwan School of Applied Foreign Languages Chung Shan Medical University Taichung Taiwan Computer Science and Info. Engineering National Central University Taiwan

ISBN: (纸本)9780769545813

SQL injection attacks, a class of injection flaw in which specially crafted input strings leads to illegal queries to databases, are one of the topmost threats to web applications. A number of research prototypes and commercial products that maintain the queries structure in web applications have been developed. But these techniques either fail to address the full scope of the problem or have limitations. Based on our observation that the injected string in a SQL injection attack is interpreted differently on different databases, in this paper, we propose a novel and effective solution TransSQL to solve this problem. TransSQL automatically translates a SQL request to a LDAP-equivalent request. After queries are executed on a SQL database and a LDAP one, TransSQL checks the difference in responses between a SQL database and a LDAP one to detect and block SQL injection attacks. Experimental results show that TransSQL is an effective and efficient solution against.SQL injection attacks. © 2011 IEEE.

关键词： computer crime

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Complexity and approximability of double digest

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Journal of Bioinformatics and Computational Biology 2005年第2期3卷 207-223页

作者： Cieliebak, Mark Eidenbenz, Stephan Woeginger, Gerhard J. Inst. of Theoretical Computer Sci. ETH Zurich 8092 Zurich Switzerland Basic and Applied Simulation Science Los Alamos National Laboratory Los Alamos NM 87545 P.O. Box 1663 United States Faculty of Electrical Engineering Mathematics/Computer Science University of Twente 7500 AE Enschede P.O. Box 217 Netherlands

We revisit the DOUBLE DIGEST problem, which occurs in sequencing of large DNA strings and consists of reconstructing the relative positions of cut sites from two different enzymes. We first show that DOUBLE DIGEST is strongly NP-complete, improving upon previous results that only showed weak NP-completeness. Even the (experimentally more meaningful) variation in which we disallow coincident cut sites turns out to be strongly NP-complete. In the second part, we model errors in data as they occur in real-life experiments: we propose several optimization variations of DOUBLE DIGEST that model partial cleavage errors. We then show that most of these variations are hard to approximate. In the third part, we investigate variations with the additional restriction that coincident cut sites are disallowed, and we show that it is NP-hard to even find feasible solutions in this case, thus making it impossible to guarantee any approximation ratio at all. © Imperial College Press.

关键词： Approximability Complexity DNA physical mapping Double digest

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Tracking the best disjunction

Tracking the best disjunction

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作者： Auer, Peter Warmuth, Manfred K. Inst. for Theor. Computer Science University of Technology Graz Klosterwiesgasse 32/2 A-8010 Graz Austria Department of Computer Science Univ. of California at Santa Cruz Applied Sciences Building Santa Cruz CA 95064

Littlestone developed a simple deterministic on-line learning algorithm for learning k-literal disjunctions. This algorithm (called WINNOW) keeps one weight for each of the n variables and does multiplicative updates to its weights. We develop a randomized version of WINNOW and prove bounds for an adaptation of the algorithm for the case when the disjunction may change over time. In this case a possible target disjunction schedule τ is a sequence of disjunctions (one per trial) and the shift size is the total number of literals that are added/removed from the disjunctions as one progresses through the sequence. We develop an algorithm that predicts nearly as well as the best disjunction schedule for an arbitrary sequence of examples. This algorithm that allows us to track the predictions of the best disjunction is hardly more complex than the original version. However, the amortized analysis needed for obtaining worst-case mistake bounds requires new techniques. In some cases our lower bounds show that the upper bounds of our algorithm have the right constant in front of the leading term in the mistake bound and almost the right constant in front of the second leading term. computer experiments support our theoretical findings. © 1998 Kluwer Academic Publishers, Boston.

关键词： Learning systems

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Secure session key distribution scheme for group communications

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Journal of Shanghai Jiaotong University (science) 2006年第2期11 E卷 192-196页

作者： Lin, Ren-Hung Jan, Jinn-Ke Inst. of Applied Mathematics National Chung Hsing Univ. Taichung 402 Taiwan Inst. of Computer Science National Chung Hsing Univ. Taichung 402 Taiwan

In a secure group communication system, messages must be encrypted before being transmitted to group members to prevent unauthorized access. In many secure group communication schemes, whenever a member leaves or joins the group, group center (GC) immediately changes the common encryption key and sends the new key to all valid members for forward and backward secrecy. If valid members are not on-line, they will miss the re-keying messages and will not be able to decrypt any ciphertext. Therefore, group members must be able to store the state of the system. In some applications, like global positioning systems (GPS) or pay-per-view systems, it is not reasonable to ask group members to stay on-line all the time and save the changes to the system. A hierarchical binary tree-based key management scheme are proposed for a secure group communication. This scheme reduces the key storage requirement of GC to a constant size and the group members are not required to be on-line constantly (stateless).

关键词： Security of data

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