62190308
On the possibility of path expressions containing backward navigations in object‐oriented databases
17923888
A personal tourism navigation system to support traveling multiple destinations with time restrictions
We propose a personal navigation system (called PNS) which navigates a tourist through multiple destinations efficiently. In our PNS, a tourist can specify multiple destinations with desired arrival/stay time and preference degree. The system calculates the route including part of the destinations satisfying tourist's requirements and navigates him/her. For the above route search problem, we have developed an efficient route search algorithm using a genetic algorithm. We have designed and implemented the PNS as a client-server system so that the portable device users can use the PNS through the Internet. Experiments using general map data and PDAs show that our PNS can calculate a semioptimal route almost in real-time.
18174475
Implication Problems for Functional Constraints on Databases Supporting Complex Objects
Virtually all semantic or object-oriented data models assume that objects have an identity separate from any of their parts and allow uses to define complex object types in which part values may be any other objects. In G. E. Weddell (ACM Trans. Database Systems17, No. 1 (1992), 32-64), a more general form of functional dependency is proposed for such models in which component attributes may correspond to descriptions of property paths, called path functional dependencies (PFDs). The main contribution of the reference is a sound and complete axiomatization for PFDs when databases may be infinite. However, a number of issues were left open which are resolved in this paper. We first prove that the same axiomatization remains complete if PFDs are permitted empty left-hand sides, but that this is not true if logical consequence is defined with respect to finite databases. We then prove that the implication problem for arbitrary PFDs is decidable. The proof suggests a means of characterizing an important function closure which is then used to derive an effective procedure for constructing a deterministic finite state automaton representing the closure. The procedure is further refined to efficient polynomial time algorithms for the implication problem for cases in which antecedent PFDs are a form of complex key constraint.
28724522
On the possibility of path expressions containing backward navigations in object-oriented databases
7202623
An Energy-Aware Video Streaming System for Portable Computing Devices
In this demonstration, we show an energy-aware video streaming system which allows users to play back video for the specified duration within the remaining battery amount. In the system, we execute a proxy server on an intermediate node in the network. It receives the video stream from a content server, transcodes it to the videos with appropriate quality, and forwards it to a PDA or a laptop PC. Here, suitable parameter values of the video (such as picture size, frame rate and bitrate) which enable playback for the specified duration are automatically calculated on the proxy using our battery consumption model. The system also allows users to play back video segments with different qualities based on the importance specified to each video segment.
16000193
Cheat detection for MMORPG on P2P environments
In this paper, we propose a new method for detecting cheat in P2P-based MMORPG. We suppose a typical P2P-based event delivery architecture where the entire game space is divided into subareas and a responsible node (selected from player terminals) delivers each event happened in the sub-area to player nodes there every predetermined time interval called timeslot. In the proposed method, we introduce multiple monitor nodes (selected from player terminals) which monitor the game state and detect cheat when it happens. In order to allow monitor nodes to track the correct game states for the corresponding subarea, we let monitor nodes and a responsible node retain a random number seed and player nodes send their events not only to responsible node but also monitor nodes so that the monitor nodes and the responsible node can uniquely calculate the latest game state from the previous game state and game events which happened during the current timeslot. Either responsible node, monitor nodes or player nodes can detect cheat by comparing hash values of game state which are retained by those nodes periodically, and role back events happened since the last correct game state. Through experiments in PlanetLab, we show that our method achieves practical performance to detect cheats.
31816332
Source location problems considering vertex-connectivity and edge-connectivity simultaneously
Let G = (V, E) be an undirected multigraph, where V and E are a set of vertices and a set of edges, respectively. Let k and l be fixed nonnegative integers. This paper considers location problems of finding a minimum-size vertex-subset S ⊆ V such that for each vertex x ∈ V the vertex-connectivity between S and x is greater than or equal to k and the edge-connectivity between S and x is greater than or equal to l. For the problem with edge-connectivity requirements, that is, k = 0, an O(L(|V|, |E|, l)) time algorithm is already known, where L(|V|, |E|, l) is the time to find all h-edge-connected components for h = 1, 2, … , l and O(L(|V|, |E|, l)) = O(|E| + |V|2 + |V|min{|E|, l|V|}min{l, |V|}) is known. In this paper, we show that the problem with k ≥ 3 is NP-hard even for l = 0. We then present an O(L(|V|, |E|, l)) time algorithm for 0 ≤ k ≤ 2 and l ≥ 0. Moreover, we prove that the problem parameterized by the size of S is fixed-parameter tractable (FPT) for k = 3 and l ≥ 0. © 2002 Wiley Periodicals, Inc.
5523130
Design for network communities
Collaboration has long been of considerable interest in the CHI community. This paper proposes and explores the concept of network communities as a crucial part of this discussion. Network communities are a form of technologymediated environment that foster a sense of community among users. We consider several familiar systems and describe the shared characteristics these systems have developed to deal with critical concerns of collaboration. Based on our own experience as designers and users of a variety of network communities. we extend this initial design space along three dimensions: the articulation of a persistent sense of location, the boundary tensions between real and virtual worlds, and the emergence and evolution of community.
45793732
Adaptive Robust Super-exponential Algorithms for Deflationary Blind Equalization of Instantaneous Mixtures
The so called “super-exponential” algorithms (SEA’s) are attractive algorithms for solving blind signal processing problems. The conventional SEA’s, however, have such a drawback that they are very sensitive to Gaussian noise. To overcome this drawback, we propose a new SEA. While the conventional SEA’s use the second- and higher-order cumulants of observations, the proposed SEA uses only the higher-order cumulants of observations. Since higher-order cumulants are insensitive to Gaussian noise, the proposed SEA is robust to Gaussian noise, which is referred to as a robust super-exponential algorithm (RSEA). The proposed RSEA is implemented as an adaptive algorithm, which is referred to as an adaptive robust super-exponential algorithm (ARSEA). To show the validity of the ARSEA, some simulation results are presented.
40447136
On Designing Relational Database Schemes for Efficient Query Processing
In relational databases, operations including joins sometimes become a cause of performance problems. We study scheme transformations to reduce the number of joins used by a class of routine database activities whose access patterns are fixed. Two scheme operations, merge and copy, are defined to transform relation schemes. The former merges two relation schemes into one, and the latter copies a functional dependency of a relation scheme to its tightly related relation scheme. Necessary and sufficient conditions are shown for applying these operations to a database scheme such that no new anomalies occur. From the necessity of the conditions, the database scheme obtained by exhaustive applications of these operations as long as the conditions hold, is optimal in the sense that further application of one of the scheme operations to the database scheme would cause anomalies. It is also proved that the resulting view of a retrieval on the original database scheme is equivalent to that of the corresponding retrieval on the new database scheme.
32882610
Membership Problems for Data Dependencies in Relational Expressions
In relational databases, a query can be formulated in terms of a relational algebra expression using projection, selection, restriction, cross product and union. In this paper, we consider a problem, called the membership problem, of determining whether a given dependency d is valid in a given relational expression E over a given database scheme R that is, whether every instance of the view scheme defined by E satisfies d (assuming that the underlying constraints in R are always satisfied). 
 
Consider the case where each relation scheme in R is associated with functional dependencies (FDs) as constraints, and d is an FD. Then the complement of the membership problem is NP-complete. However, if E contains no union, then the membership problem can be solved in polynomial time. Furthermore, if E contains neither a union nor a projection, then we can construct in polynomial time a cover for valid FDs in E, that is, a set of FDs which implies every valid FD in E. 
 
Consider the case where each relation scheme in R is associated with multivalued dependencies (MVDs) as well as FDs, and d is an FD or an MVD. Even if E consists of selections and cross products only, the membership problem is NP-hard. However, if E contains no union, and each relation scheme name in R occurs in E at most once, then the membership problem can be solved in polynomial time. As a corollary of this result, it can be determined in polynomial time whether a given FD or MVD is valid in R1⋈⋯⋈Rs, where R1,…,Rs are relation schemes with FDs and MVDs, and Ri⋈Rj is the natural join of Ri and Rj.