For complex queries in parallel database systems, substantial amounts of data must be redistributed between operators executed on different processing nodes. Frequently, such intermediate results cannot be held in main memory and must be stored on disk. To limit the ensuing performance penalty, a data allocation must be found that supports parallel I/O to the greatest possible extent. In this paper, we propose declustering even self-contained units of temporary data processed in a single operation (such as individual buckets of parallel hash joins) across multiple disks. Using a suitable analytical model, we find that the improvement of parallel I/O outweighs the penalty of increased fragmentation.

Skew effects are a serious problem in parallel database systems, but the relationship between different skew types and load balancing methods is still not fully understood. We develop and compare two classifications of skew effects and load balancing strategies, respectively, to match their relevant properties. Our conclusions highlight the importance of highly dynamic scheduling to optimize both the complexity and the success of load balancing. We also suggest the tuning of database schemata as a new anti-skew measure.

We describe a new WWW-based information system called Squirrel which demonstrates an attempt to integrate a relational database system (RDBS) with an information retrieval system (IRS) providing context based access to a SGML document collection. Indexing of the documents is performed on full-text basis whereas search capabilities include ranking of the retrieved documents. A functioning prototype has been implemented and is available on the Internet.

In this article, a design methodology for complex composite aircraft structures is presented. The developed approach combines a multi-objective optimization method and a parameterized simulation model using a design concept database. Due to the combination of discrete and continuous design variables describing the structures, evolutionary algorithms are used within the presented optimization approach. The approach requires an evaluation of the design alternatives that is performed by parameterized simulation models. The variability of these models is achieved using a design concept database that contains different layouts for each implemented structural part. Due to the complexity of the generated aircraft structures, the finite element method is applied for the calculation of the structural behaviour. The applicability of the developed design approach will be demonstrated by optimizing two composite aircraft fuselage examples. The obtained results show that the developed methodology is useful and reliable for designing complex aircraft structures.

An index in a database system interacts with many of the software modules in the system. For systems supporting a wide range of index structures, interfacing the index code with the rest of the system poses a great problem. The problems are an order of magnitude more for adding new access methods to the system. These problems could be reduced manifold if common interfaces could be specified for different access methods. It would be even better, if these interfaces could be made database-system independent. This thesis addresses the problem of defining generic index interfaces for access methods in database systems. It concentrates on two specific issues: First, specification of a complete set of abstract interfaces that would work for all access methods and for all database systems. Second, optimized query processing for all data types including userdefined data types. An access method in a database system can be considered to be made up of three specific parts: Upper interfaces, lower interfaces, and type interfaces. An access method interacts with a database system through its upper interfaces, lower interfaces and type interfaces. Upper interfaces consist of the functions an index provides to a database system. Lower interfaces are the database-system dependent software modules an index has to interact with, to accomplish any system related functions. Type interfaces consist of the set of functions an index uses, which interpret the data type. These three parts together characterize an access method in a database system. This splitting of an access method makes it possible to define generic interfaces. In this thesis, we will discuss each of these three different interfaces in detail, identify functionalities and design clear interfaces. The design of these interfaces promote development of type-independent and database-system independent access methods.

This is a bachelor thesis concerning the response time and CPU effects of indexing in relational databases. Analyzing two popular databases, PostgreSQL and MariaDB with a real-world database structure using randomized entries. The experiment was conducted over Docker and its command-line interface without cached values to ensure fair outcomes. The procedure was done throughout seven different CRUD queries with multiple volumes of database entries to discover their strengths and weaknesses when utilizing indexes. The result chapter shows indicators that indexing has an overall enhancing effect on almost all of the queries. It is found that join, update and delete operations benefits the most from non-clustered indexing. PostgreSQL gains the most from indexes while MariaDB has a minuscule improvement in the response time reduction. A greater usage of CPU resources does not seem to correlate with quicker response times.

By allowing judgments based on a small number of exemplar documents to be applied to a larger number of unexamined documents, clustered presentation of search results represents an intuitively attractive possibility for reducing the cognitive resource demands on human users of information retrieval systems. However, clustered presentation of search results is sensible only to the extent that naturally occurring similarity relationships among documents correspond to topically coherent clusters. The Cluster Hypothesis posits just such a systematic relationship between document similarity and topical relevance. To date, experimental validation of the Cluster Hypothesis has proved problematic, with collection-specific results both supporting and failing to support this fundamental theoretical postulate. The present study consists of two computational information visualization experiments, representing a two-tiered test of the Cluster Hypothesis under adverse conditions. Both experiments rely on multidimensionally scaled representations of interdocument similarity matrices. Experiment 1 is a term-reduction condition, in which descriptive titles are extracted from Associated Press news stories drawn from the TREC information retrieval test collection. The clustering behavior of these titles is compared to the behavior of the corresponding full text via statistical analysis of the visual characteristics of a two-dimensional similarity map. Experiment 2 is a dimensionality reduction condition, in which inter-item similarity coefficients for full text documents are scaled into a single dimension and then rendered as a two-dimensional visualization; the clustering behavior of relevant documents within these unidimensionally scaled representations is examined via visual and statistical methods. Taken as a whole, results of both experiments lend strong though not unqualified support to the Cluster Hypothesis. In Experiment 1, semantically meaningful 6.6-word document surrogates systematically conform to the predictions of the Cluster Hypothesis. In Experiment 2, the majority of the unidimensionally scaled datasets exhibit a marked nonuniformity of distribution of relevant documents, further supporting the Cluster Hypothesis. Results of the two experiments are profoundly question-specific. Post hoc analyses suggest that it may be possible to predict the success of clustered searching based on the lexical characteristics of users' natural-language expression of their information need.

The first step of the program is to input the statistical information concerning the relations of th· database. This information is stored in the log file and the file matrix data structures. Next, the query itself is read and stored in an array called the query matrix. The program examines the various fields of this matrix and decides which relations in the database are necessary to answer the query. For these relations it determines those attributes which should be eliminated and those which should be preserved for further processing. The key attributes are identified and are projected along with the other attributes. After the initial projection is completed the sizes of the new temporary relations are evaluated and stored in the appropriate fields of the file matrix structure. The program then examines that part of the query which contains the various restrictions on the attributes. The values of the attributes are sorted and those values which do not match the restrictions are eliminated from the log file. Again, the sizes of the new relations are estimated according to the method described by Egyhazy et al. [6]. A second projection is performed to eliminate attributes which were required by the selection phase but are not part of the final answer to the query. The remaining relations are those relations which need to be joined to form a relation with the required information. In order to decide upon which relations to join, a special table, the join matrix, is created. This table contains pairs of relations which have common attributes and common values and therefore are joinable. The LP algorithm is used to determine the least expensive join out of all the possible joins. This process is repeated until all of the relations are joined to form a single relation which answers the query. As in the case of projection and selection the size of the temporary relations after each join is estimated. As a last step, we remove the key attributes which helped in joining the files but are not part of the answer to the query. / Master of Engineering

Academic librarians routinely assist faculty seeking information on diverse topics. Librarians may overlook potentially useful information, however, if they are unaware of faculty interests that are not mentioned in a specific request. At the East Tennessee State University (ETSU) Medical Library, a team of librarians developed a faculty interests database to improve reference services and collection development. This paper describes the creation and implementation of the database and the faculty response.

Abstract available in the Proceedings of Ninety-first Annual Meeting Medical Library Association, Inc. San Francisco, California May 31-June 6, 1991.