Advances in Real-Time Database Systems Research Special Section on RTDBS of ACM SIGMOD Record 25(1), March 1996.

A Real-Time DataBase System (RTDBS) can be viewed as an amalgamation of a conventional DataBase Management System (DBMS) and a real-time system. Like a DBMS, it has to process transactions and guarantee ACID database properties. Furthermore, it has to operate in real-time, satisfying time constraints imposed on transaction commitments. A RTDBS may exist as a stand-alone system or as an embedded component in a larger multidatabase system. The publication in 1988 of a special issue of ACM SIGMOD Record on Real-Time DataBases signaled the birth of the RTDBS research area -- an area that brings together researchers from both the database and real-time systems communities. Today, almost eight years later, I am pleased to present in this special section of ACM SIGMOD Record a review of recent advances in RTDBS research. There were 18 submissions to this special section, of which eight papers were selected for inclusion to provide the readers of ACM SIGMOD Record with an overview of current and future research directions within the RTDBS community. In this paper [below], I summarize these directions and provide the reader with pointers to other publications for further information. -Azer Bestavros, Guest Edito

NoDoSE - A tool for Semi-Automatically Extracting Structured and Semistructured Data from Text Documents.

Often interesting structured or semistructured data is not in database systems but in HTML pages, text files, or on paper. The data in these formats is not usable by standard query processing engines and hence users need a way of extracting data from these sources into a DBMS or of writing wrappers around the sources. This paper describes NoDoSE, the Northwestern Document Structure Extractor, which is an interactive tool for semi-automatically determining the structure of such documents and then extracting their data. Using a GUI, the user hierarchically decomposes the file, outlining its interesting regions and then describing their semantics. This task is expedited by a mining component that attempts to infer the grammar of the file from the information the user has input so far. Once the format of a document has been determined, its data can be extracted into a number of useful forms. This paper describes both the NoDoSE architecture, which can be used as a test bed for structure mi..

Pro ject Synopsis: Evaluating STRIP

Abstract Ths paper describes preliminary e orts at evaluating the performance of the Stanford realtime informationprocessor STRIP v2.0. We desribe a benchmark for active real-time databases based on a program trading application and report STRIP's performance on this benchmark

Project Synopsis: Evaluating STRIP

Ths paper describes preliminary efforts at evaluating the performance of the Stanford realtime information processor (STRIP v2.0). We desribe a benchmark for active real-time databases based on a program trading application and report STRIP's performance on this benchmark. Keywords: derived data, view maintenance, active database system, transaction scheduling, program trading, real-time database system. 1 Introduction The Stanford real-time information processor (STRIP) is a soft real-time main memory database system with special facilities for importing and exporting data as well as handling derived data. Data can be imported into (and exported from) STRIP using the stream interface, which allows STRIP to maintain materialized views of remote and very rapidly changing data. In addition, a sophisticated rule system supports the efficient maintenance of derived data over rapidly changing base data. This paper summarizes our efforts to benchmark the performance of STRIP v2.0. It also ..

Emulating Soft Real-Time Scheduling Using Traditional Operating System Schedulers

Real-time scheduling algorithms are usually only available in the kernels of real-time operating systems, and not in more general purpose operating systems, like Unix. For some soft real-time problems, a traditional operating system may be the development platform of choice. This paper addresses methods of emulating real-time scheduling algorithms on top of standard time-share schedulers. We examine (through simulations) three strategies for priority assignment within a traditional multi-tasking environment. The results show that the emulation algorithms are comparable in performance to the real-time algorithms and in some instances outperform them. Keywords: soft real-time, priority assignment, scheduling. 1 Introduction In this paper we focus on "soft real-time" applications, which have the following characteristics: ffl tasks have real-time deadlines; ffl missing some task deadlines is acceptable; ffl the goal is to minimize the number of missed deadlines; ffl task arrival and..

On Building Distributed Soft Real-Time Systems

When building a distributed real-time system, one can either build the whole system from scratch, or from pre-existing standard components. Although the former allows better scheduling design, it is not economical in terms of the cost and time of development. This paper studies the performance of distributed soft real-time systems that use standard components with various scheduling algorithms and suggests ways to improve them. Keywords: soft real-time, distributed systems, deadline assignment, priority assignment, scheduling. 1 Introduction Consider a distributed system for stock market analysis and program trading. In this application, information on stock prices may be gathered from multiple information sources and piped through a series of filters for refinement. The refined information may then be stored in a database server to be queried by, for example, an expert system that spots trading opportunities. The expert system may then trigger certain buy-and-sell actions to realize ..

Applying Update Streams in a Soft Real-Time Database System

Many papers have examined how to efficiently export a materialized view but to our knowledge none have studied how to efficiently import one. To import a view, i.e., to install a stream of updates, a real-time database system must process new updates in a timely fashion to keep the database "fresh," but at the same time must process transactions and ensure they meet their time constraints. In this paper, we discuss the various properties of updates and views (including staleness) that affect this tradeoff. We also examine, through simulation, four algorithms for scheduling transactions and installing updates in a soft real-time database. Keywords: soft real-time, temporal databases, materialized views, updates. 1 Introduction The problem we study in this paper arose during the on-going implementation of the STRIP real-time database system. 1 This system [AGMK94b] provides traditional database services (e.g., SQL, indexing, recovery) with real-time facilities (e.g., transaction dead..