A homogeneous relational model and query languages for temporal databases

Abstract

In a temporal database, time values are associated with data item to indicate their periods of validity. We propose a model for temporal databases within the framework of the classical database theory. Our model is realized as a temporal parameterization of static relations. We do not impose any restrictions upon the schemes of temporal relations. The classical concepts of normal forms and dependencies are easily extended to our model, allowing a suitable design for a database scheme. We present a relational algebra and a tuple calculus for our model and prove their equivalence. Our data model is homogeneous in the sense that the periods of validity of all the attributes in a given tuple of a temporal relation are identical. We discuss how to relax the homogeneity requirement to extend the application domain of our approach.

Relational model of temporal data based on 6th normal form

“…In that sense, our proposal is comparable with the data model discussed in [8], where the temporal domain within a tuple does not change from one attribute to another.…”

“…According to the definition in [8], the relations in the model are homogeneous, which differs from the proposal [7], where a different SINCE value may be used for each temporal attribute in a temporal relation containing current information. In that sense, our proposal is comparable with the data model discussed in [8], where the temporal domain within a tuple does not change from one attribute to another.…”

“…Assuming that our proposal fits particularly well with temporal data, then the occasional normalization of non-temporal attributes is not too critical. Gadia proposed a homogeneous relational model where normalization leads to homogeneous relations with an identical validity for all attributes in a given tuple of a temporal relation [8]. By using only 6NF, the proposed model is in accordance with Gadia's concept and therefore homogeneous.…”

A Tale of Two Schemas: Creating a Temporal XML Schema from a Snapshot Schema with τXSchema

“…Relying on ad hoc methods limits data independence. The designer of a schema for time-varying data has to make a variety of decisions, such as whether to timestamp with periods or with temporal elements [16], which are sets of non-overlapping periods and which elements should be time-varying. By adopting a tiered approach, where the snapshot XML Schema, temporal annotations, and physical annotations are separate documents, individual schema design decisions can be specified and changed, often without impacting the other design decisions, or indeed, the processing of tools.…”

A survey of schema versioning issues for database systems

“…The relational model (Codd 1970) and its extension (Codd 1979) provide for a logically complete language with which to describe data transformations (Codd 1972) and a number of time-related algebras have been proposed to extend the static relational model (Clifford and Tansel 1985;Tansel 1986;Clifford and Croker 1987;McKenzie and Snodgrass 1987a, 1987cGadia 1988;Lorentzos and Johnson 1988;Sarda 1990;Tuzhilin and Clifford 1990). A survey of valid-time and bitemporal algebras is given in McKenzie and Snodgrass (1991) which includes an evaluation of twelve representative algebras against various criteria.…”