Evaluation of relational algebras incorporating the time dimension in databases

Abstract

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 criteria are shown to be mutually unsatisfiable, implying there can be no perfect temporal algebra, Choices made as to which of the incompatible criteria are satisfied characterize existing algebras Twelve time-oriented algebras are summarized and then evaluated against the criteria. We demonstrate that the design space has in some sense been explored in that all combinations of basic design decisions have at least one representative algebra. Coverage of the remaining criteria provides one measure of the quality of each algebra We argue that all of the criteria are independent and that the criteria identified as compatible are indeed so, Finally, we list plausible properties proposed by others that are either subsumed by other criteria, are not well defined, or have no objective basis for being evaluated. The algebras realize many different approaches to what appears initially to be a straightforward design task.

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

“…Currently there is no separation of elements or attributes based on the relative frequency of update. In the situation that some elements (for example) vary at a significantly different rate than other elements, it may prove more efficient to split the schema up into pieces such that elements with similar "rates of change" are together [25,29,32]. This would avoid redundant repetition of elements that do not change as frequently.…”

“…Indeed, that has been the approach taken by many researchers for the relational and object-oriented models [25,29,32]. As we will discuss in detail, that approach inherently introduces difficulties with respect to document validation, data independence, tool support, and standardization.…”

A survey of schema versioning issues for database systems

“…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. Of these, only the proposals by McKenzie andSnodgrass 1987b, 1990;McKenzie 1988) are extended to deal explicitly with schema evolution 3 .…”

How Would You Like to Aggregate Your Temporal Data?

“…As a result, data management is currently an overly involved and error-prone activity. Temporal database research [3,9,10,12,37,40] has produced several dozen proposals for temporal data models [31,38] and query languages [4,21,22,34,39] that aim to remedy this situation. This paper focuses on an increasingly important area of temporal data management, namely aggregation (e.g., [2,6,14,23,36,41]).…”