Richard S. Brice

InfoSleuth: agent-based semantic integration of information in open and dynamic environments

The goal of the InfoSleuth project at MCC is to exploit and synthesize new technologies into a unified system that retrieves and processes information in an ever-changing network of information sources. InfoSleuth has its roots in the Carnot project at MCC, which specialized in integrating heterogeneous information bases. However, recent emerging technologies such as internetworking and the World Wide Web have significantly expanded the types, availability, and volume of data available to an information management system. Furthermore, in these new environments, there is no formal control over the registration of new information sources, and applications tend to be developed without complete knowledge of the resources that will be available when they are run. Federated database projects such as Carnot that do static data integration do not scale up and do not cope well with this ever-changing environment. On the other hand, recent Web technologies, based on keyword search engines, are scalable but, unlike federated databases, are incapable of accessing information based on concepts. In this experience paper, we describe the architecture, design, and implementation of a working version of InfoSleuth. We show how InfoSleuth integrates new technological developments such as agent technology, domain ontologies, brokerage, and internet computing, in support of mediated interoperation of data and services in a dynamic and open environment. We demonstrate the use of information brokering and domain ontologies as key elements for scalability.

Performance of a database manager in a virtual memory system

Buffer space is created and managed in database systems in order to reduce accesses to the I/O devices for database information. In systems using virtual memory any increase in the buffer space may be accompanied by an increase in paging. The effects of these factors on system performance are quantified where system performance is a function of page faults and database accesses to I/O devices. This phenomenon is examined through the analysis of empirical data gathered in a multifactor experiment. The factors considered are memory size, size of buffer space, memory replacement algorithm, and buffer management algorithm. The improvement of system performance through an increase in the size of the buffer space is demonstrated. It is also shown that for certain values of the other factors an increase in the size of the buffer space can cause performance to deteriorate.

An extension of the performance of a database manager in a virtual memory system using partially locked virtual buffers

Buffer pools are created and managed in database systems in order to reduce the total number of accesses to the I/O devices. In systems using virtual memory, any reduction in I/O accesses may be accompanied by an increase in paging. The effects of these factors on system performance are quantified, where system performance is a function of page faults and database accesses to the I/O devices. A previous study of this phenomenon is extended through the analysis of empirical data gathered in a multifactor experiment. In this study memory is partitioned between the program and the buffer so that the impact of the controlled factors can be more effectively evaluated. It is possible to improve system performance through the use of different paging algorithms in the program partition and the buffer partition. Also, the effects on system performance as the virtual buffer size is increased beyond the real memory allocated to the buffer partition are investigated.

The InfoSleuth Project

The InfoSleuth Project at MCC [7, 9, 8, 1] is developing and deploying technologies for finding information in corp~ rate networks and in external networka, such as networks baaed on the emerging National Information Infrastructure. InfoSleuth is baaed on MCC’S previously developed Carnot technology [2, 6, 10], which was successfully used to integrate heterogeneous information resources. The Carnot project developed semantic modeling techniques that enable description of the information resources and pioneered the use of agents to provide interoperation among autonomous systems. The InfoSleuth Project investigates the use of Carnot technologies in a dynamically changing environment, such as the Internet, where there is no formal control of the registration of new information sources and the identities of the resources to be used may be unknown at the time the application is developed. InfoSleuth deploys semantic agents [9, 5, 3] that carry out coordinated searches and cooperate with each other to merge the retrieved data into understandable information. The project is developing technologies to support mediated interoperation of data and services over information networks in a dynamically changing environment, including:

Feedback coupled resource allocation policies in the multiprogramming-multiprocessor computer system

Model studies of some integrated, feedback-driven scheduling systems for multiprogrammed-multiprocessor computer systems are presented. The basic control variables used are the data-flow rates for the processes executing on the CPU. The model systems feature simulated continuous-flow and preempt-resume scheduling of input-output activity. Attention is given to the amount of memory resource required for effective processing of the I/O activity (buffer space assignment). The model studies used both distribution-driven and trace-driven techniques. Even relatively simple dynamic schedulers are shown to improve system performance (as measured by user CPU time) over that given by optimal or near-optimal static schedulers imbedded in identical system structures and workload environments. The improvement is greatest under a heavy I/O demand workload.

I/O buffer performance in a virtual memory system

In this study we construct a simulator of a data base management system running in a virtual memory environment. We use the simulator to investigate the value of using an I/O buffer in this environment. The simulator is driven by trace data obtained with a software probe. The simulator is validated and is used to verify a theoretical model which predicts paging and disk access rates produced by use of an I/O buffer in a virtual memory environment. Results from a multi-factor set of simulation experiments are analyzed. The factors include three page replacement algorithms, four buffer management algorithms, five virtual buffer sizes, three values for real memory and six well known and widely differing distributions for creating sequences of requests to the simulated data base management system.

Performance of a data base manager in a virtual memory system

Buffer pools are created and managed in data base systems in order to reduce the total amount of accesses to the I/O devices. The use of the buffer pool in a virtual storage system may cause an increase in the page fault rate. We examine this phenomenon through the analysis of empirical data gathered in a multifactor experiment. The factors we considered were memory size, buffer size, replacement algorithm for memory and buffer management algorithm.