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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)
Outline • Temporal database • Real-time database Temporal Database • Time as an important domain • Valid time and transaction time – Valid time models events in reality – Trans. time models facts known by database • Temporal data, Temporal database – A database that supports some aspect of time. – He went to live on his own in Bigtown. Although he moved out(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)
This document 1 contains deenitions of a wide range of concepts speciic to and widely used within temporal databases. In addition to providing deenitions, the document also includes explanations of concepts as well as discussions of the adopted names. The consensus eort that lead to this glossary was initiated in Early 1992. The present glossary subsumes(More)
Although &#8220;<italic>now</italic>&#8221; is expressed in SQL and CURRENT_TIMESTAMP within queries, this value cannot be stored in the database. How ever, this notion of an ever-increasing current-time value has been reflected in some temporal data models by inclusion of database-resident variables, such as &#8220;<italic>now</italic>&#8221;(More)