28724522
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.
29071607
Eigenvector Algorithms with Reference Signals for Frequency Domain BSS
This paper describes blind source separation (BSS) problems in the frequency domain using an eigenvector algorithm (EVA) with reference signals. The proposed EVA has such an attractive feature that all source signals are separated simultaneously from their mixtures. This is an advantage against the methods using deflation process (e.g., super-exponential method), because those methods sometimes do not work so as to converge to desired solutions, due to deflation failure. Computer simulation demonstrates the validity of the proposed EVA.
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.
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.
14842083
The network communities of SeniorNet
With the explosion of participation on the Internet, there is increasing interest and speculation in extending its uses to support diverse online communities, and particular interest in using the Internet to combat loneliness and isolation amongst senior citizens For the past year, we have been investigating SeniorNet (SN), a 12 year old organization that attempts to bring seniors together via computer networking technologies. We found a rich tapestry of human relationships supported by various technical and social underpinnings. In this paper, we delve into the richness of an active community and describe the intertwining technical and social factors that make it valuable and useful for its members. An underlying question in these discussions is "If network communities have to be principally created and maintained by their members (as we posit), then how do designers help without getting in the way?".
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.