<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 temporal database contains time-varying data. In a real-time database transactions have deadlines or timing constraints. In this paper we review the substantial research in these two previously separate areas. First we characterize the time domain; then we investigate temporal and real-time data models. We evaluate temporal and real-time query languages… (More)
Database needs are changing, driven by the Internet and increasing amounts of scientific and sensor data. In this article, the authors propose research into several important new directions for database management systems.
The relational algebra is a procedural query language for relational databases. In this paper we survey extensions of the relational algebra that can query databases recording time-varying data. Such an algebra is a critical part of a temporal DBMS. We identify 26 criteria that provide an objective basis for evaluating temporal algebras, Seven of the… (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)
This paper provides a systematic and comprehensive study of the semantics of temporal databases. We rst examine how facts may be associated with time, speciically with one or more dimensions of valid time and transaction time. One common case is that of a bitemporal relation, in which facts are associated with exactly one valid time and one transaction… (More)