Binary decision diagrams (BDD's) are graph representations of Boolean functions, and at the same time they can be regarded as a computational model. In this paper, we discuss relations between BDD's and other computational models and clarify the computational power of BDD's. BDD's have the property that each variable is examined only once according to a total order of the variables. We characterize families of BDD's by on-line deterministic Turing machines and families of permutations. To clarify the computational power of BDD's, we discuss the difference of the computational power with respect to the way of reading inputs. We also show that the language TADGAP (Topologically Arranged Deterministic Graph Accessibility Problem) is simultaneously complete for both of the class U-PolyBDD of languages accepted by uniform families of polynomial-size BDD's and the clas DL of languages accepted by log-space bounded deterministic Turing machines. From the results, we can see that the problem whether U-PolyBDD U-NC¹ is equivalent to a famous open problem whether DL U-NC¹, where U-NC¹ is the class of languages accepted by uniform families of log-depth constant fan-in logic circuits.

Finite state translation systems (fsts') are a widely studied computational model in the area of tree automata theory. In this paper, the string generating capacities of fsts' and their subclasses are studied. First, it is shown that the class of string languages generated by deterministic fsts' equals to that of parallel multiple context-free grammars, which are an extension of context-free grammars. As a corollary, it can be concluded that the recognition problem for a deterministic fsts is solvable in O(n^e1)-time, where n is the length of an input word and e is a constant called the degree of the deterministic fsts'. In contrast to the latter fact, it is also shown that nondeterministic monadic fsts' with state-bound 2 can generate an NP-complete language.

We present outside-in conditional narrowing for orthogonal conditional term rewriting systems, and show the completeness of leftmost-outside-in conditional narrowing with respect to normalizable solutions. We consider orthogonal conditional term rewriting systems whose conditions consist of strict equality only. Completeness results are obtained for systems both with and without extra variables. The result bears practical significance since orthogonal conditional term rewriting systems can be viewed as a computation model for functional-logic programming languages and leftmost-outside-in conditional narrowing is the computing mechanism for the model.

An Ordered Binary Decision Diagram (BDD) is a graph representation of a Boolean function. According to its good properties, BDD's are widely used in various applications. In this paper, we investigate the computational complexity of basic operations on BDD's. We consider two important operations: reduction of a BDD and binary Boolean operations based on BDD's. This paper shows that both the reduction of a BDD and the binary Boolean operations based on BDD's are NC¹-reducible to REACHABILITY. That is, both of the problems belong to NC². In order to extend the results to the BDD's with output inverters, we also considered the transformations between BDD's and BDD's with output inverters. We show that both of the transformations are also NC¹-reducible to REACHBILITY.

Nested relational models were proposed as natural extensions of the relational model to support new emerging database applications. Prototype implementations of nested relational database systems (NRDBSs) have been done by some research groups. However, there remain many research issues on nested relations. One important issue is query processing, in particular query optimization. In NRDBSs, efficient execution of queries involving hierarchical data structures inherent in nested relations is required. In this paper, we focus on two join-type operations on nested relations: nested join and embed, and propose an algorithm to derive a cost optimal execution sequence of nested joins and embeds for a given query graph. The cost optimality of the derived sequence is formally proved. The complexity of the algorithm is proved to be O(N ²), when N nested relations are included in the query graph.

ADTs (Abstract Data Types) have been known as a promising feature for extending the database applications to CAD/CAM and other engineering areas. This extension has brought a new dimension to query optimization. Conventional query optimization methods, which considers only joins as the dominant cost factor, are based on the belief that the executions of selections and projections basically take no time. However, in databases that support ADTs, this may not be true since the execution of a selection involving ADT functions may be very time-cosuming. Thus selections with ADT functions should not be considered as inexpensive operations in queries, and the conventional optimization heuristics should be enhanced to correspond to the appearance of the queries of this kind. In this paper, we show the possibility that semijoins can be used as an effective means to reduce the number of evaluations of an ADT function and consequently optimize queries containing expensive ADT selections. We suggest the enhancement of an conventional optimization heuristics by adding a semijoins pre-stage which is an additional component corresponding to expensive ADT selections. By this way, the applicable range of the conventional heuristics are extended to hold the ability of handling queries with ADT functions. Several optimization algorithms are given and some simulation results show the effectiveness of our methods.

Distributed algorithms that entail successive rounds of message exchange are called decentralized consensus protocols. Several consensus protocols use a finite projective plane as a communication structure and require 4nn messages in two rounds, where n is the number of nodes. This paper presents an efficient communication structure that uses a finite projective plane with a duality of indices. The communication structure requires 2nn messages in two rounds, and can therefore halve the number of messages. It is shown that a finite projective plane with a duality can be constructed from a difference set, and that the presented communication structure has two kinds of symmetry.

An approach to estimate the information of moving objects is described in terms of their kinetic and static properties such as 2D velocity, acceleration, position, and the size of each object for the features of motion snd shape. To obtain the information of motion/shape of multiple objects, an advanced contour matching scheme is developed, which includes the synthesis of edge images and the analysis of object shape with a high matching confidence as well as a low computation cost. The scheme is composed of three algorithms: a motion estimation by an iterative triple cross-correlation, an image synthesis by shifting and masking the object, and a shape analysis for determining the object size. Implementing fuzzy membership functions to the object shape, the scheme gets improved in accuracy of capturing motion and shape of multiple moving objects. Experimental result shows that the proposed method is valid for several walking men in real scene.

This paper discusses a new image resolution conversion method which converts not only spatial resolution but also amplitude resolution. This method involves considering impulse responses of image devices and human visual characteristics, and can preserve high image quality. This paper considers a system that digitizes the multilevel input image with high spatial resolution and low amplitude resolution using an image scanner, and outputs the image with low spatial resolution and high amplitude resolution on a CRT display. The algorithm thus reduces the number of pixels while increasing the number of brightness levels. Since a CRT display is chosen as the output device, the distribution of each spot in the display, which is modeled as a Gaussian function, is taken as the impulse response. The output image is then expressed as the summation of various amplitudes of the impulse response. Furthermore, human visual perception, which bears a nonlinear relationship to the spatial frequency component, is simplified and modeled with a cascade combination of low-pass and high-pass filters. The output amplitude is determined so that the error between the output image and the input image, after passing through the visual perception filter, is minimized. According to the results of a simulation, it is shown that image quality can be largely preserved by the proposed method, while significant image information is lost by conventional methods.

A method is presented to perform image segmentation by accumulatively observing apparent motion in a long image sequence of a dynamic scene. In each image in the sequence, locations are grouped into small patches of approximately uniform optical flow. To reduce the noise in computed flow vectors, a local image motion vector of each patch is computed by averaging flow vectors in the corresponding patches in several images. A segment contains patches belonging to the same 3-D plane in the scene. Initial segments are obtained in the image, and then an attempt to merge or split segments is iterated to update the segments. In order to remove inherent ambiguities in motion-based segmentation, temporal coherence between the local image motion of a patch and the apprent motion of every plane is investigated over long time. In each image, a patch is grouped into the segment of the plane whose apparent motion is temporally most coherent with the local image motion of the patch. When apparent motions of two planes are temporally incoherent, segments of the planes are retained as individual ones.

With the advent of an aging society, the incidence of Alzheimer-type dementia (hereinafter referred to as AD for convenience) has drastically increased. Compared with classic cerebrovascular dementia, AD requires different therapeutic modalities. Despite such differences, it is difficult to establish a differential diagnosis of AD and cerebrovascular dementia. In the present paper, we analyze the neuropsychological symptoms and signs associated with AD, such as visual cognitive dysfunction, with particular attention to head and eye coordination. The subjects were allowed to gaze at targets disposed 1 m away and at a visual angle of 25 and 50 in order to compare healthy volunteers and patients with senile dementias such as multi-infarct dementia (MID). As a consequence, patients with AD presented clinical manifestations not seen in patients with other senile dementias; that is, (1) an increase in stepwise eye movement, (2) anisotropy in the velocity of right-directional and left-directional eye movements, (3) a decrease in the velocity of head movements (4) incomplete gaze, and (5) decreased head share.

Let S(n) be a space constructible function such that S(n) log n. In this paper, we show that AuxSpTu (S(n),T(n)) NSPACE (S(n)log T(n)), where AuxSpTu (S(n),T(n)) is the class of languages accepted by nondeterministic auxiliary pushdown automata operating simultaneously in O(S(n)) space and O(T(n)) turns of the auxiliary tape head.

There have been several interesting investigations on the space functions constructed by one-dimensional or two-dimensional Turing machines. On the other hand, as far as we know, there is no investigation about the space functions constructed by three-dimensional Turing machines. In this paper, we investigate about space constructibility by three-dimensional deterministic Turing machines with cubic inputs, and show that the functions log^*n and log^(k)n, k1, are fully space constructible by these machines.