Yeow Meng Chee

Keyword Search in Spatial Databases: Towards Searching by Document

This work addresses a novel spatial keyword query called the m-closest keywords (mCK) query. Given a database of spatial objects, each tuple is associated with some descriptive information represented in the form of keywords. The mCK query aims to find the spatially closest tuples which match m user-specified keywords. Given a set of keywords from a document, mCK query can be very useful in geotagging the document by comparing the keywords to other geotagged documents in a database. To answer mCK queries efficiently, we introduce a new index called the bR*-tree, which is an extension of the R*-tree. Based on bR*-tree, we exploit a priori-based search strategies to effectively reduce the search space. We also propose two monotone constraints, namely the distance mutex and keyword mutex, as our a priori properties to facilitate effective pruning. Our performance study demonstrates that our search strategy is indeed efficient in reducing query response time and demonstrates remarkable scalability in terms of the number of query keywords which is essential for our main application of searching by document.

Constructions for

This paper introduces a new combinatorial construction for q-ary constant-weight codes which yields several families of optimal codes and asymptotically optimal codes. The construction reveals intimate connection between q-ary constant-weight codes and sets of pairwise disjoint combinatorial designs of various types

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An Infinite Class of Balanced Vectorial Boolean Functions with Optimum Algebraic Immunity and Good Nonlinearity.- Separation and Witnesses.- Binary Covering Arrays and Existentially Closed Graphs.- A Class of Three-Weight and Four-Weight Codes.- Equal-Weight Fingerprinting Codes.- Problems on Two-Dimensional Synchronization Patterns.- A New Client-to-Client Password-Authenticated Key Agreement Protocol.- Elliptic Twin Prime Conjecture.- Hunting for Curves with Many Points.- List Decoding of Binary Codes-A Brief Survey of Some Recent Results.- Recent Developments in Low-Density Parity-Check Codes.- On the Applicability of Combinatorial Designs to Key Predistribution for Wireless Sensor Networks.- On Weierstrass Semigroups of Some Triples on Norm-Trace Curves.- ERINDALE: A Polynomial Based Hashing Algorithm.- A Survey of Algebraic Unitary Codes.- New Family of Non-Cartesian Perfect Authentication Codes.- On the Impossibility of Strong Encryption Over .- Minimum Distance between Bent and Resilient Boolean Functions.- Unconditionally Secure Approximate Message Authentication.- Multiplexing Realizations of the Decimation-Hadamard Transform of Two-Level Autocorrelation Sequences.- On Cayley Graphs, Surface Codes, and the Limits of Homological Coding for Quantum Error Correction.

-Ary Constant-Weight Codes

A problem of index coding with side information was first considered by Birk and Kol in 1998. In this study, a generalization of index coding scheme, where transmitted symbols are subject to errors, is studied. Error-correcting methods for such a scheme, and their parameters, are investigated. In particular, the following question is discussed: given the side information hypergraph of index coding scheme and the maximal number of erroneous symbols δ , what is the shortest length of a linear index code, such that every receiver is able to recover the required information? This question turns out to be a generalization of the problem of finding a shortest length error-correcting code with a prescribed error-correcting capability in the classical coding theory. The Singleton bound and two other bounds, referred to as the α-bound and the κ -bound, for the optimal length of a linear error-correcting index code (ECIC) are established. For large alphabets, a construction based on concatenation of an optimal index code with a maximum distance separable classical code is shown to attain the Singleton bound. For smaller alphabets, however, this construction may not be optimal. A random construction is also analyzed. It yields another inexplicit bound on the length of an optimal linear ECIC. Further, the problem of error-correcting decoding by a linear ECIC is studied. It is shown that in order to decode correctly the desired symbol, the decoder is required to find one of the vectors, belonging to an affine space containing the actual error vector. The syndrome decoding is shown to produce the correct output if the weight of the error pattern is less or equal to the error-correcting capability of the corresponding ECIC. Finally, the notion of static ECIC, which is suitable for use with a family of instances of an index coding problem, is introduced. Several bounds on the length of static ECICs are derived, and constructions for static ECICs are discussed. Connections of these codes to weakly resilient Boolean functions are established.

Coding and Cryptology

Influence maximization is a fundamental research problem in social networks. Viral marketing, one of its applications, is to get a small number of users to adopt a product, which subsequently triggers a large cascade of further adoptions by utilizing “Word-of-Mouth” effect in social networks. Time plays an important role in the influence spread from one user to another and the time needed for a user to influence another varies. In this paper, we propose the time constrained influence maximization problem. We show that the problem is NP-hard, and prove the monotonicity and submodularity of the time constrained influence spread function. Based on this, we develop a greedy algorithm. To improve the algorithm scalability, we propose the concept of Influence Spreading Path in social networks and develop a set of new algorithms for the time constrained influence maximization problem. We further parallelize the algorithms for achieving more time savings. Additionally, we generalize the proposed algorithms for the conventional influence maximization problem without time constraints. All of the algorithms are evaluated over four public available datasets. The experimental results demonstrate the efficiency and effectiveness of the algorithms for both conventional influence maximization problem and its time constrained version.

Error Correction for Index Coding With Side Information

Reliability is a major concern in the design of large disk arrays. Hellerstein et al. pioneered the study of erasure-resilient codes that allow one to reconstruct the original data even in the presence of disk failures. In this paper, we take a set systems view of the problem of constructing erasure-resilient codes. This leads to interesting extremal problems in finite set theory. Solutions to some of these problems are characterized by well-known combinatorial designs. In other instances, combinatorial designs are shown to give asymptotically exact solutions to these problems. As a result, we improve, extend and generalize previous results of Hellerstein et al.

Influence Spreading Path and Its Application to the Time Constrained Social Influence Maximization Problem and Beyond

The design of large libraries of oligonucleotides having constant-content and satisfying Hamming distance constraints between oligonucleotides and their Watson-Crick complements is important in reducing hybridization errors in DNA computing, DNA microarray technologies, and molecular bar coding. Various techniques have been studied for the construction of such oligonucleotide libraries, ranging from algorithmic constructions via stochastic local search to theoretical constructions via coding theory. A new stochastic local search method is introduced, which yields improvements for more than one third of the benchmark lower bounds of Gaborit and King (2005) for n-mer oligonucleotide libraries when n les 14. Several optimal libraries are also found by computing maximum cliques on certain graphs.

Asymptotically optimal erasure-resilient codes for large disk arrays

We show an interesting pairwise balanced design (PBD)-closure result for the set of lengths of constant-composition codes whose distance and size meet certain conditions. A consequence of this PBD-closure result is that the size of optimal constant-composition codes can be determined for infinite families of parameter sets from just a single example of an optimal code. As an application, the sizes of several infinite families of optimal constant-composition codes are derived. In particular, the problem of determining the size of optimal constant-composition codes having distance four and weight three is solved for all lengths sufficiently large. This problem was previously unresolved for odd lengths, except for lengths seven and eleven.

Improved Lower Bounds for Constant GC-Content DNA Codes

Security aspects of the index coding with side information (ICSI) problem are investigated. Building on the results of Bar-Yossef (2006), the properties of linear index codes are further explored. The notion of weak security, considered by Bhattad and Narayanan (2005) in the context of network coding, is generalized to block security. It is shown that the linear index code based on a matrix <i>L</i>, whose column space code <i>C</i>(<i>L</i>) has length <i>n</i>, minimum distance <i>d</i> , and dual distance <i>d</i>^⊥ , is (<i>d</i>-1-<i>t</i>) -block secure (and hence also weakly secure) if the adversary knows in advance <i>t</i> ≤ <i>d</i>-2 messages, and is completely insecure if the adversary knows in advance more than <i>n</i> - <i>d</i>^⊥ messages. Strong security is examined under the conditions that the adversary: 1) possesses <i>t</i> messages in advance; 2) eavesdrops at most μ transmissions; 3) corrupts at most δ transmissions. We prove that for sufficiently large <i>q</i> , an optimal linear index code which is strongly secure against such an adversary has length κ_q+μ+2δ . Here, κ_q is a generalization of the min-rank over F_q of the side information graph for the ICSI problem in its original formulation in the work of Bar-Yossef et al.

The PBD-Closure of Constant-Composition Codes

The concept of group divisible codes, a generalization of group divisible designs with constant block size, is introduced in this paper. This new class of codes is shown to be useful in recursive constructions for constant-weight and constant-composition codes. Large classes of group divisible codes are constructed which enabled the determination of the sizes of optimal constant-composition codes of weight three (and specified distance), leaving only four cases undetermined. Previously, the sizes of constant-composition codes of weight three were known only for those of sufficiently large length.