8870380
Performance analysis of three related assignment problems
The relative placement of records in a database has a significant impact on the overall system performance. In this paper we study three related assignment problems. They are (1) the assignment of records to devices so as to minimize the expected completion time and to maximize the expected utilization of the devices, (2) the assignment of records to pages or blocks in secondary memory so as to minimize the number of blocks to be accessed, and (3) the analysis of the performance of a hashing scheme under the assumption that the record-to-bucket probability varies from one bucket to another. The solutions to these problems are obtained by studying an occupancy problem. In each case, an optimal solution is obtained.
14189953
Adaptive record clustering
An algorithm for record clustering is presented. It is capable of detecting sudden changes in users' access patterns and then suggesting an appropriate assignment of records to blocks. It is conceptually simple, highly intuitive, does not need to classify queries into types, and avoids collecting individual query statistics. Experimental results indicate that it converges rapidly; its performance is about 50 percent better than that of the total sort method, and about 100 percent better than that of randomly assigning records to blocks.
11887466
On a partitioning problem
This paper investigates the problem of locating a set of “boundary points” of a large number of records. Conceptually, the boundary points partition the records into subsets of roughly the same number of elements, such that the key values of the records in one subset are all smaller or all larger than those of the records in another subset. We guess the locations of the boundary points by linear interpolation and check their accuracy by reading the key values of the records on one pass. This process is repeated until all boundary points are determined. Clearly, this problem can also be solved by performing an external tape sort. Both analytical and empirical results indicate that the number of passes required is small in comparison with that in an external tape sort. This kind of record partitioning may be of interest in setting up a statistical database system.
5051365
Promising Approach to Distributed Query Processing
2822009
An Approach to Probabilistic Retrieval
The objective is to relate the effectiveness of retrieval, the fuzzy set concept and the processing of Boolean query. The use of a probabilistic retrieval scheme is motivated. It is found that there is a correspondence between probabilistic retrieval schmes and fuzzy sets. A fuzzy set corresponding to a potentially optimal probabilistic retrieval scheme is obtained. Then the retrieval scheme for the fuzzy set is constructed.
12799586
Data broadcast for time-constrained read-only transactions in mobile computing systems
In this paper we propose broadcast algorithms, based on the policies proposed in previous studies, to disseminate data items to time-constrained read-only transactions. In the proposed algorithms, the number of data items requested by a transaction will be considered explicitly in selecting the data items for broadcast. The purpose of the algorithms is to reduce the number of transactions missing their deadlines, and to minimize their mean response time. A detailed simulation model of a mobile computing system has been developed and extensive simulation experiments have been performed to study the performance characteristics of the proposed broadcast algorithms, and the results show that our broadcast algorithms outperform previously proposed algorithms.
2162231
A Robust Line-Feature-Based Hausdorff Distance for Shape Matching
The Hausdorff distance can be used to measure the similarity of two point sets. In matching the two point sets. one of the point sets is translated. rotated and scaled in order to obtain an optimal matching. which is a computationally intensive process. In this paper, a robust line-feature-based approach for model-based recognition is proposed. which can achieve a good performance level in matching, even in a noisy environment or with the existence of occlusion. The method is insensitive to noise and can find the rotation and scale of the image point set accurately and reliably. For this reason, instead of 4D matching, a 2D-2D matching algorithm can be used. This can greatly reduce the required memory and computation. Having rotated and scaled the image point set, the difference between the query point set and the model point set can be computed by considering translation only. The performance and the sensitivity to noise of our algorithm are evaluated using simulated data. Experiments show that our 2D-2D algorithm can give a high performance level when determining the relative scale and orientation of two point sets.
8292420
Priority Scheduling of Transactions in Distributed Real-Time Databases
One of the most important issues in the design of distributed real-time database system (DRTDBS) is transaction scheduling which consists of two parts: priority scheduling and real-time concurrency control. In the past studies, mostly, these issues are studied separately although they have a very close interaction with each other. In this paper, we propose new priority assignment policies for DRTDBS and study their impact on two typical real-time concurrency control protocols (RT-CCPs), High Priority Two Phase Locking (HP-2PL) and Optimistic Concurrency Control with Broadcast Commit (OCC-BC). Our performance results show that many factors, such as data conflict resolution, degree of data contention and transaction restarts, that are unique to database systems, have significant impact on the performance of the policies which in turn affect the performance of the real-time concurrency control protocols. OCC-BC is more affected by the priority assignment policies than HP-2PL owing to the late detection of conflict. In the design of priority assignment policies, we have found that neither the purely deadline driven policies nor data contention driven policies are suitable for DRTDBS. Our proposed policy, the Mixed Method (MM), which considers both transaction timeliness and data contention, outperforms other policies over a wide range of system parameter settings.
27689226
Virtual deadline assignment in distributed real-time database systems
In recent years, the performance of distributed real-time database systems (DRTDBS) have been examined using different simulation models. In these models, the network issues are always being neglected. The networks are usually modeled as simple constant delay servers. However, it is found that the performance of the underlying network has significant impact on the overall performance of the DRTDBS. The results also showed that unpredictable behavior of the underlying network will give non-constant network transit time which in turn deter the overall system performance. To deal with this impact, different virtual deadline assignment schemes are proposed. The schemes assign a virtual deadline based on the current network condition to those transactions which require a comparatively better performance. Our results demonstrate that dynamically tuning the virtual deadlines of transactions depending on the condition of the network, yields a substantial improvement in the performance of that certain type of transactions without severely affecting the overall system performance.
12206604
An adaptive active contour model for highly irregular boundaries
Abstract Snake is an active contour model for representing image contours. In this paper, we propose an efficient active contour model which can represent highly irregular boundaries. The algorithm includes an adaptive force along the contour, and adjusts the number of points for the snake according to the desired boundary. A better stopping criterion based on the area of a closed contour is devised. Furthermore, in this method, a contour can break automatically to represent the contours of multiple objects. Experiments show that this method can extract object's boundaries accurately and efficiently.