Yahiko Kambayashi

Transformation rules for designing CNOT-based quantum circuits

This paper gives a simple but nontrivial set of local transformation rules for Control-NOT(CNOT)-based combinatorial circuits. It is shown that this rule set is complete, namely, for any two equivalent circuits, S1 and S2, there is a sequence of transformations, each of them in the rule set, which changes S1 to S2. Our motivation is to use this rule set for developing a design theory for quantum circuits whose Boolean logic parts should be implemented by CNOT based circuits. As a preliminary example, we give a design procedure based on our transformation rules which reduces the cost of CNOT-based circuits.

A longest common subsequence algorithm suitable for similar text strings

SummaryEfficient algorithms for computing the longest common subsequence (LCS for short) are discussed. O(pn) algorithm and O(p(m-p) log n) algorithm [Hirschberg 1977] seem to be best among previously known algorithms, where p is the length of an LCS and m and n are the lengths of given two strings (m≦n). There are many applications where the expected length of an LCS is close to m.In this paper, O(n(m-p)) algorithm is presented. When p is close to m (in other words, two given strings are similar), the algorithm presented here runs much faster than previously known algorithms.

Public Applications of SpaceTag and Their Impacts

SpaceTag is an object that can be accessed only from limited locations and time period. SpaceTags are served and distributed from a central server which should be managed by a service provider. Users of the SpaceTag system can access SpaceTags with portable terminals equipped with location sensors and wireless communication device such as mobile phones. Users walk around in a city and find SpaceTags that can be only found at the location. SpaceTag is thus an inconvenient media, but suitable for gaming, advertising, city guide information, etc. A user can also put a SpaceTag at the location where (s)he is, which can be found by other people nearby. This feature also enables local public communication applications. In this paper, we will argue why this inconvenient but simple virtual platform can support various applications for a digital city. We will also argue social impacts of these applications.

Deputy mechanisms for object-oriented databases

Concepts of deputy objects and deputy classes for object-oriented databases (OODBs) are introduced. They can be used for unified realization of object views, roles and migration. The previous researches on these concepts were carried out separately, although they are very closely related. Objects appearing in a view can be regarded as playing roles in that view. Object migration is caused by change of roles of an object. Deputy objects can be used for unified treatment of them and generalization of these concepts. The schemata of deputy objects are defined by deputy classes. A set of algebraic operations are developed for deputy class derivation. In addition, three procedures for update propagation between deputy objects and source objects have been designed, which can support dynamic classification. The unified realization of object views, roles and migration by deputy mechanisms can achieve the following advantages. (1) Treating view objects as roles of an object allows them to have additional attributes and methods so that the autonomous views suitable for OODBs can be realized. (2) Handling object roles in the same way as object views enables object migration to be easily realized by dynamic classification functions of object views. (3) Generalization of object views, roles and migration makes it possible that various semantic constraints on them can, be defined and enforced uniformly.<<ETX>>

SpaceTag: an overlaid virtual system and its applications

SpaceTag is an object system on which each object called SpaceTag can be accessed only from limited locations and a limited time period. Its applications include entertainment systems, advertisement services, bulletin board systems, and personal communication systems. For one-way communication, they are broadcasted from the server; for two-way communication, users can cut and paste SpaceTags between their portable PCs and the real space. The SpaceTag system is a location-aware information system, as well as an augmented reality system because it attaches information to the real space. However, we categorize it as an overlaid virtual system, because it has no direct link to real objects. It can be realized as a public service without causing drastic change of this society, and without much cost.

Query processing for distributed databases using generalized semi-joins

In distributed database systems, the cost to process a query is mainly determined by the amount of communication. Semi-join is a very useful tool to reduce the cost of joins in such systems. There are, however, queries called cyclic ones which cannot be processed by semi-joins only. In this paper the concept of generalized semi-joins is introduced to solve such a problem. To handle an arbitrary cyclic query, first a spanning tree is selected in the corresponding query graph and then generalized semi-joins are applied in the order determined by the tree. Processing of cyclic queries, however, requires more communication cost than processing of tree queries, since in the former case we need to transmit attribute values which are not required in the latter case. A procedure to reduce the communication cost of such additional data is developed, which will make the generalized semi-join based procedures practical.

Tight bounds on the number of states of DFAs that are equivalent to n -state NFAs

The specification discloses wheel and axle assemblies in each of which a sealing washer serves both as a bearing seal and a thrust washer. The washer has a thicker, belled thrust washer portion and an outer, thinner, belled flange hinged to the thrust washer portion by a thin hinge portion. The flange acts as a wiper or seal on the hub of a golf cart wheel and the thrust washer portion sealingly engages an axle mounting the wheel.

Advances in Database Technologies

In this paper, we propose a fuzzy attribute-oriented induction method for knowledge discovery in relational databases. This method is adapted from the DBLearn system by representing background knowledge with fuzzy thesauri and fuzzy labels. These models allow to take into account inherent imprecision and uncertainty of the domain representation. We also show the power of fuzzy thesauri and linguistic variables to describe gradations in the generalization process and to handle exceptions.

Recent Advances and Research Problems in Data Warehousing

In the recent years, the database community has witnessed the emergence of a new technology, namely data warehousing. A data warehouse is a global repository that stores pre-processed queries on data which resides in multiple, possibly heterogeneous, operational or legacy sources. The information stored in the data warehouse can be easily and efficiently accessed for making effective decisions. The On-Line Analytical Processing (OLAP) tools access data from the data warehouse for complex data analysis, such as multidimensional data analysis, and decision support activities. Current research has lead to new developments in all aspects of data warehousing, however, there are still a number of problems that need to be solved for making data warehousing effective. In this paper, we discuss recent developments in data warehouse modelling, view maintenance, and parallel query processing. A number of technical issues for exploratory research are presented and possible solutions are discussed.

Communication through virtual active objects overlaid onto the real world

A SpaceTag is a virtual object that can be accessed only from limited locations and time period. Users of the SpaceTag System can see and create SpaceTags using a portable terminal with a location sensor. We have categorized it as an overlaid virtual system, in which virtual objects are overlaid onto the real world based on time and space coordinates. This architecture is more promising, general purpose, low-cost, and more realistic than other location-aware system architectures like augmented reality that attaches virtual information onto real objects. The SpaceTag System can be offered as a public information service that is a common platform for gaming, advertising, city guide information, etc. We have already implemented a prototype. In this paper, active SpaceTags are additionally proposed. They are enabled to interact autonomously with human and other SpaceTags, realizing new applications of interactive games, virtual creatures (SpacePet), etc. The computation model of active SpaceTag is described here. This paper also gives a discussion by regarding the SpaceTag System as a CVE. It is a considered as special CVE that has a same space/time coordinates as the real world. SpaceTags and SpacePets can be regarded as objects and active objects in the virtual space, but they are projected onto the real world. Users can communicate with each other through these objects. This paper also describes how such communication occurs.