Richard T. Snodgrass

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<i>Recently, attention has been focussed on</i> historical databases <i>(HDBs), representing an enterprise over time. We have developed a new language,</i> TQuel, <i>to query an HDB. TQuel is a superset of Quel, the query language in the Ingres relational database management system. This paper provides an overview of the language, motivating the various(More)
• a short biography of John Doe. – born on April 3rd, 1975 in Smallville. His birth was registered on April 4th, 1975. – He went to live on his own in Bigtown. Although he moved out on August 26th, 1994, he forgot to register the change of address officially. – He updated his record on December 27, 1994. – John Doe was accidentally hit by a truck on April(More)
1 Dipartimento di Scienze dell'Informazione, Universit~ degli Studi di Milano, Milano, Italy bettini@dsi, unimi, i t , http ://mercurio. sm. dsi. unimi, it/'bert ini/ 2 Department of Computer Science, James Cook University, Townsville, Australia curtis@cs, j cu. edu. au, http: I/w~z. cs. j cu. edu. au/" curt is/ 3 Department of Computer Science, University(More)
A wide range of database applications manage time-varying information. Existing database technology currently provides little support for managing such data. The research area of temporal databases has made important contributions in characterizing the semantics of such information and in providing expressive and efficient means to model, store, and query(More)
In <italic>valid-time indeterminacy</italic> it is known that an event stored in a database did in fact occur, but it is not known exactly <italic>when</italic>. In this paper we extend the SQL data model and query language to support valid-time indeterminacy. We represent the occurrence time of an event with a set of possible instants, delimiting when the(More)
Monitoring is an essential part of many program development tools, and plays a central role in debugging, optimization, status reporting, and reconfiguration. Traditional monitoring techniques are inadequate when monitoring complex systems such as multiprocessors or distributed systems. A new approach is described in which a historical database forms the(More)
Aggregate computation, such as selecting the minimum attribute value of a relation, is expensive, especially in a temporal database. We describe the basic techniques behind computing aggregates in conventional databases and show that these techniques are not efficient when applied to temporal databases. We examine the problem of computing constant intervals(More)