OpenRaiser/Intern-Atlas huggingface dataset:
Multi-skill Collaborative Teams based on Densest Subgraphs
Venue: arXiv cs.SI 2011
Year: 2011

We consider the problem of identifying a team of skilled individuals for collaboration, in the presence of a social network. Each node in the social network may be an expert in one or more skills. Edge weights specify affinity or collaborative compatibility between respective nodes. Given a project that requires a set of specified number of skilled individuals in each area of expertise, the goal is to identify a team that maximizes the collaborative compatibility. For example, the requirement may be to form a team that has at least three databases experts and at least two theory experts. We explore team formation where the collaborative compatibility objective is measured as the density of the induced subgraph on selected nodes. The problem of maximizing density is NP-hard even when the team requires individuals of only one skill. We present a 3-approximation algorithm that improves upon a naive extension of the previously known algorithm for densest at least $k$ subgraph problem. We further show how the same approximation can be extended to a special case of multiple skills. Our problem generalizes the formulation studied by Lappas et al. [KDD '09] who measure team compatibility in terms of diameter or spanning tree costs. Experiments are performed on a crawl of the DBLP graph where individuals can be skilled in at most four areas - theory, databases, data mining, and artificial intelligence. In addition to our main algorithm, we also present heuristic extensions to trade off between the size of the solution and its induced density. These density-based algorithms outperform the diameter-based objective on several metrics for assessing the collaborative compatibility of teams. The solutions suggested are also intuitively meaningful and scale well with the increase in the number of skilled individuals required.
Generic Programming of Reusable, High Performance Container Types using Automatic Type Hierarchy Inference and Bidirectional Antichain Typing
Venue: arXiv cs.PL 2011
Year: 2011

We introduce a new compile-time notion of type subsumption based on type simulation. We show how to apply this static subsumption relation to support a more intuitive, object oriented approach to generic programming of reusable, high performance container types. As a first step towards an efficient implementation of the resulting type system in a compiler we present a novel algorithm for bidirectional type inference over arbitrary syntax graphs. The algorithm uses the new static type subsumption relation to compress the data that has to be stored for each node in the typeflow graph. During typeflow analysis this means that the set of types for a given node can be symbolically represented using antichains instead of using bitvectors or some other explicit set representation. This results in a typing algorithm that is both flexible and precise and shows good performance on representative instances.
Benchmark Problems for Totally Unimodular Set System Auction
Venue: arXiv cs.GT 2011
Year: 2011

We consider a generalization of the $k$-flow set system auction where the set to be procured by a customer corresponds to a feasible solution to a linear programming problem where the coefficient matrix and right-hand-side together constitute a totally unimodular matrix. Our results generalize and strengthen bounds identified for several benchmarks, which form a crucial component in the study of frugality ratios of truthful auction mechanisms.
Cooperative Defense against Pollution Attacks in Network Coding Using SpaceMac
Venue: arXiv cs.CR 2011
Year: 2011

Intra-session network coding is known to be vulnerable to pollution attacks. In this work, first, we introduce a novel homomorphic MAC scheme called SpaceMac, which allows an intermediate node to verify if its received packets belong to a specific subspace, even if the subspace is expanding over time. Then, we use SpaceMac as a building block to design a cooperative scheme that provides complete defense against pollution attacks: (i) it can detect polluted packets early at intermediate nodes and (ii) it can identify the exact location of all, even colluding, attackers, thus making it possible to eliminate them. Our scheme is cooperative: parents and children of any node cooperate to detect any corrupted packets sent by the node, and nodes in the network cooperate with a central controller to identify the exact location of all attackers. We implement SpaceMac in both C/C++ and Java as a library, and we make the library available online. Our evaluation on both a PC and an Android device shows that (i) SpaceMac's algorithms can be computed quickly and efficiently, and (ii) our cooperative defense scheme has low computation and significantly lower communication overhead than other comparable state-of-the-art schemes.
Even Better Framework for min-wise Based Algorithms
Venue: arXiv cs.DS 2011
Year: 2011

In a recent paper from SODA11 \cite{kminwise} the authors introduced a general framework for exponential time improvement of \minwise based algorithms by defining and constructing almost \kmin independent family of hash functions. Here we take it a step forward and reduce the space and the independent needed for representing the functions, by defining and constructing a \dkmin independent family of hash functions. Surprisingly, for most cases only 8-wise independent is needed for exponential time and space improvement. Moreover, we bypass the $O(\log{\frac{1}ε})$ independent lower bound for approximately \minwise functions \cite{patrascu10kwise-lb}, as we use alternative definition. In addition, as the independent's degree is a small constant it can be implemented efficiently. Informally, under this definition, all subsets of size $d$ of any fixed set $X$ have an equal probability to have hash values among the minimal $k$ values in $X$, where the probability is over the random choice of hash function from the family. This property measures the randomness of the family, as choosing a truly random function, obviously, satisfies the definition for $d=k=|X|$. We define and give an efficient time and space construction of approximately \dkmin independent family of hash functions. The degree of independent required is optimal, i.e. only $O(d)$ for $2 \le d < k=O(\frac{d}{ε^2})$, where $ε\in (0,1)$ is the desired error bound. This construction can be used to improve many \minwise based algorithms, such as \cite{sizeEstimationFramework,Datar02estimatingrarity,NearDuplicate,SimilaritySearch,DBLP:conf/podc/CohenK07}, as will be discussed here. To our knowledge such definitions, for hash functions, were never studied and no construction was given before.
Parallel algorithms for SAT in application to inversion problems of some discrete functions
Venue: arXiv cs.DC 2011
Year: 2011

In this article we consider the inversion problem for polynomially computable discrete functions. These functions describe behavior of many discrete systems and are used in model checking, hardware verification, cryptanalysis, computer biology and other domains. Quite often it is necessary to invert these functions, i.e. to find an unknown preimage if an image and algorithm of function computation are given. In general case this problem is computationally intractable. However, many of it's special cases are very important in practical applications. Thus development of algorithms that are applicable to these special cases is of importance. The practical applicability of such algorithms can be validated by their ability to solve the problems that are considered to be computationally hard (for example cryptanalysis problems). In this article we propose the technology of solving the inversion problem for polynomially computable discrete functions. This technology was implemented in distributed computing environments (parallel clusters and Grid-systems). It is based on reducing the inversion problem for the considered function to some SAT problem. We describe a general approach to coarse-grained parallelization for obtained SAT problems. Efficiency of each parallelization scheme is determined by the means of a special predictive function. The proposed technology was validated by successful solving of cryptanalysis problems for some keystream generators. The main practical result of this work is a complete cryptanalysis of keystream generator A5/1 which was performed in a Grid system specially built for this task.
Optimality of Network Coding in Packet Networks
Venue: arXiv cs.IT 2011
Year: 2011

We resolve the question of optimality for a well-studied packetized implementation of random linear network coding, called PNC. In PNC, in contrast to the classical memoryless setting, nodes store received information in memory to later produce coded packets that reflect this information. PNC is known to achieve order optimal stopping times for the many-to-all multicast problem in many settings. We give a reduction that captures exactly how PNC and other network coding protocols use the memory of the nodes. More precisely, we show that any such protocol implementation induces a transformation which maps an execution of the protocol to an instance of the classical memoryless setting. This allows us to prove that, for any (non-adaptive dynamic) network, PNC converges with high probability in optimal time. In other words, it stops at exactly the first time in which in hindsight it was possible to route information from the sources to each receiver individually. Our technique also applies to variants of PNC, in which each node uses only a finite buffer. We show that, even in this setting, PNC stops exactly within the time in which in hindsight it was possible to route packets given the memory constraint, i.e., that the memory used at each node never exceeds its buffer size. This shows that PNC, even without any feedback or explicit memory management, allows to keep minimal buffer sizes while maintaining its capacity achieving performance.
Cooperative Interference Control for Spectrum Sharing in OFDMA Cellular Systems
Venue: arXiv cs.IT 2011
Year: 2011

This paper studies cooperative schemes for the inter-cell interference control in orthogonal-frequency-divisionmultiple- access (OFDMA) cellular systems. The downlink transmission in a simplified two-cell system is examined, where both cells simultaneously access the same frequency band using OFDMA. The joint power and subcarrier allocation over the two cells is investigated for maximizing their sum throughput with both centralized and decentralized implementations. Particularly, the decentralized allocation is achieved via a new cooperative interference control approach, whereby the two cells independently implement resource allocation to maximize individual throughput in an iterative manner, subject to a set of mutual interference power constraints. Simulation results show that the proposed decentralized resource allocation schemes achieve the system throughput close to that by the centralized scheme, and provide substantial throughput gains over existing schemes.
Fairness issues in a chain of IEEE 802.11 stations
Venue: arXiv cs.NI 2011
Year: 2011

We study a simple general scenario of ad hoc networks based on IEEE 802.11 wireless communications, consisting in a chain of transmitters, each of them being in the carrier sense area of its neighbors. Each transmitter always attempts to send some data frames to one receiver in its transmission area, forming a pair sender-receiver. This scenario includes the three pairs fairness problem, and allows to study some fairness issues of the IEEE 802.11 medium access mechanism. We show by simulation that interesting phenomena appear, depending on the number n of pairs in the chain and of its parity. We also point out a notable asymptotic behavior. We introduce a powerful modeling, by simply considering the probability for a transmitter to send data while its neighbors are waiting. This model leads to a non-linear system of equations, which matches very well the simulations, and which allows to study both small and very large chains. We then analyze the fairness issue in the chain regarding some parameters, as well as the asymptotic behavior. By studying very long chains, we notice good asymptotic fairness of the IEEE 802.11 medium sharing mechanism. As an application, we show how to increase the fairness in a chain of three pairs.
Derandomizing HSSW Algorithm for 3-SAT
Venue: arXiv cs.CC 2011
Year: 2011

We present a (full) derandomization of HSSW algorithm for 3-SAT, proposed by Hofmeister, Schöning, Schuler, and Watanabe in [STACS'02]. Thereby, we obtain an O(1.3303^n)-time deterministic algorithm for 3-SAT, which is currently fastest.
Synchronizing Objectives for Markov Decision Processes
Venue: arXiv cs.LO 2011
Year: 2011

We introduce synchronizing objectives for Markov decision processes (MDP). Intuitively, a synchronizing objective requires that eventually, at every step there is a state which concentrates almost all the probability mass. In particular, it implies that the probabilistic system behaves in the long run like a deterministic system: eventually, the current state of the MDP can be identified with almost certainty. We study the problem of deciding the existence of a strategy to enforce a synchronizing objective in MDPs. We show that the problem is decidable for general strategies, as well as for blind strategies where the player cannot observe the current state of the MDP. We also show that pure strategies are sufficient, but memory may be necessary.
Contract-Based Cooperative Spectrum Sharing
Venue: arXiv cs.NI 2011
Year: 2011

Providing proper economic incentives is essential for the success of dynamic spectrum sharing. Cooperative spectrum sharing is one effective way to achieve this goal. In cooperative spectrum sharing, secondary users (SUs) relay traffics for primary users (PUs), in exchange for dedicated transmission time for the SUs' own communication needs. In this paper, we study the cooperative spectrum sharing under incomplete information, where SUs' types (capturing their heterogeneity in relay channel gains and evaluations of power consumptions) are private information and not known by PUs. Inspired by the contract theory, we model the network as a labor market. The single PU is the employer who offers a contract to the SUs. The contract consists of a set of contract items representing combinations of spectrum accessing time (i.e., reward) and relaying power (i.e., contribution). The SUs are employees, and each of them selects the best contract item to maximize his payoff. We study the optimal contract design for both weak and strong incomplete information scenarios. First, we provide necessary and sufficient conditions for feasible contracts in both scenarios. In the weak incomplete information scenario, we further derive the optimal contract that achieves the same maximum PU's utility as in the complete information benchmark. In the strong incomplete information scenario, we propose a Decompose-and-Compare algorithm that achieves a close-to-optimal contract. We future show that the PU's average utility loss due to the suboptimal algorithm and the strong incomplete information are both relatively small (less than 2% and 1:3%, respectively, in our numerical results with two SU types).
Bounds on the Achievable Rate for the Fading Relay Channel with Finite Input Constellations
Venue: arXiv cs.IT 2011
Year: 2011

We consider the wireless Rayleigh fading relay channel with finite complex input constellations. Assuming global knowledge of the channel state information and perfect synchronization, upper and lower bounds on the achievable rate, for the full-duplex relay, as well as the more practical half-duplex relay (in which the relay cannot transmit and receive simultaneously), are studied. Assuming the power constraint at the source node and the relay node to be equal, the gain in rate offered by the use of relay over the direct transmission (without the relay) is investigated. It is shown that for the case of finite complex input constellations, the relay gain attains the maximum at a particular SNR and at higher SNRs the relay gain tends to become zero. Since practical schemes always use finite complex input constellation, the above result means that the relay offers maximum advantage over the direct transmission when we operate at a particular SNR and offers no advantage at very high SNRs. This is contrary to the results already known for the relay channel with Gaussian input alphabet.
Theoretical Count of Function Points for Non-Measurable Items
Venue: arXiv cs.SE 2011
Year: 2011

This paper studies and proposes a technique of function point counting for items classified as non-measurable. The main objective is to expand the conventional technique of counting to ensure that this comprises consistently the tasks involved in building portals and sites in general. In addition, it also applies to measure the cost of continued activities related to these web applications. The extended technique is potentially useful to measure several products associated with information systems, including periodicals publishable in intranets.
P ORTOLAN: a Model-Driven Cartography Framework
Venue: arXiv cs.OH 2011
Year: 2011

Processing large amounts of data to extract useful information is an essential task within companies. To help in this task, visualization techniques have been commonly used due to their capacity to present data in synthesized views, easier to understand and manage. However, achieving the right visualization display for a data set is a complex cartography process that involves several transformation steps to adapt the (domain) data to the (visualization) data format expected by visualization tools. To maximize the benefits of visualization we propose Portolan, a generic model-driven cartography framework that facilitates the discovery of the data to visualize, the specification of view definitions for that data and the transformations to bridge the gap with the visualization tools. Our approach has been implemented on top of the Eclipse EMF modeling framework and validated on three different use cases.
Effective protocols for low-distance file synchronization
Venue: arXiv cs.IT 2011
Year: 2011

Suppose that we have two similar files stored on different computers. We need to send the file from the first computer to the second one trying to minimize the number of bits transmitted. This article presents a survey of results known for this communication complexity problem in the case when files are "similar" in the sense of Hamming distance. We mainly systematize earlier results obtained by various authors in 1990s and 2000s and discuss its connection with coding theory, hashing algorithms and other domains of computer science. In particular cases we propose some improvements of previous constructions.
A nearly-mlogn time solver for SDD linear systems
Venue: arXiv cs.DS 2011
Year: 2011

We present an improved algorithm for solving symmetrically diagonally dominant linear systems. On input of an $n\times n$ symmetric diagonally dominant matrix $A$ with $m$ non-zero entries and a vector $b$ such that $A\bar{x} = b$ for some (unknown) vector $\bar{x}$, our algorithm computes a vector $x$ such that $||{x}-\bar{x}||_A < ε||\bar{x}||_A $ {$||\cdot||_A$ denotes the A-norm} in time $${\tilde O}(m\log n \log (1/ε)).$$ The solver utilizes in a standard way a `preconditioning' chain of progressively sparser graphs. To claim the faster running time we make a two-fold improvement in the algorithm for constructing the chain. The new chain exploits previously unknown properties of the graph sparsification algorithm given in [Koutis,Miller,Peng, FOCS 2010], allowing for stronger preconditioning properties. We also present an algorithm of independent interest that constructs nearly-tight low-stretch spanning trees in time $\tilde{O}(m\log{n})$, a factor of $O(\log{n})$ faster than the algorithm in [Abraham,Bartal,Neiman, FOCS 2008]. This speedup directly reflects on the construction time of the preconditioning chain.
New Worst-Case Upper Bound for X3SAT
Venue: arXiv cs.AI 2011
Year: 2011

The rigorous theoretical analyses of algorithms for exact 3-satisfiability (X3SAT) have been proposed in the literature. As we know, previous algorithms for solving X3SAT have been analyzed only regarding the number of variables as the parameter. However, the time complexity for solving X3SAT instances depends not only on the number of variables, but also on the number of clauses. Therefore, it is significant to exploit the time complexity from the other point of view, i.e. the number of clauses. In this paper, we present algorithms for solving X3SAT with rigorous complexity analyses using the number of clauses as the parameter. By analyzing the algorithms, we obtain the new worst-case upper bounds O(1.15855m), where m is the number of clauses.
Achievable rates for transmission of discrete constellations over the Gaussian MAC channe
Venue: arXiv cs.IT 2011
Year: 2011

In this paper we consider the achievable rate region of the Gaussian Multiple Access Channel (MAC) when suboptimal transmission schemes are employed. Focusing on the two-user MAC and assuming uncoded Pulse Amplitude Modulation (PAM), we derive a rate region that is a pentagon, and propose a strategy with which it can be achieved. We also compare the region with outer bounds and with orthogonal transmission.
An Adaptive Multimedia-Oriented Handoff Scheme for IEEE 802.11 WLANs
Venue: arXiv cs.NI 2011
Year: 2011

Previous studies have shown that the actual handoff schemes employed in the IEEE 802.11 Wireless LANs (WLANs) do not meet the strict delay constraints placed by many multimedia applications like Voice over IP. Both the active and the passive supported scan modes in the standard handoff procedure have important delay that affects the Quality of Service (QoS) required by the real-time communications over 802.11 networks. In addition, the problem is further compounded by the fact that limited coverage areas of Access Points (APs) occupied in 802.11 infrastructure WLANs create frequent handoffs. We propose a new optimized and fast handoff scheme that decrease both handoff latency and occurrence by performing a seamless prevent scan process and an effective next-AP selection. Through simulations and performance evaluation, we show the effectiveness of the new adaptive handoff that reduces the process latency and adds new context-based parameters. The Results illustrate a QoS delay-respect required by applications and an optimized AP-choice that eliminates handoff events that are not beneficial.
Specifying Data Bases Management Systems by Using RM-ODP Engineering Language
Venue: arXiv cs.DB 2011
Year: 2011

Distributed systems can be very large and complex. The various considerations that influence their design can result in a substantial specification, which requires a structured framework that has to be managed successfully. The purpose of the RMODP is to define such a framework. The Reference Model for Open Distributed Processing (RM-ODP) provides a framework within which support of distribution, inter-working and portability can be integrated. It defines: an object model, architectural concepts and architecture for the development of ODP systems in terms of five viewpoints. Which include an information viewpoint. Since the usage of Data bases management systems (DBMS) in complex networks is increasing considerably, we are interested, in our work, in giving DBMS specifications through the use of the three schemas (static, dynamic, invariant). The present paper is organized as follows. After a literature review, we will describe then the subset of concepts considered in this work named the database management system (DBMS) object model. In the third section, we will be interested in the engineering language and DMBS structure by describing essentially DBMS objects. Finally, we will present DBMS engineering specifications and makes the connection between models and their instances. This introduces the basic form of the semantic approach we have described here.