Showing papers by "Christian S. Jensen published in 1995"

An Architectural, Framework

Abstract: In this chapter we address the question of how to construct a DBMS architecture supporting TSQL2. Our goal is to enumerate the changes that a conventional DBMS would need to support TSQL2. We are concerned with modifying a conventional DBMS in a minimal fashion to support TSQL2. While a more elaborate architecture is possible (likely with significant performance gains), our purpose is to describe the “first step” towards the realization of a temporal DBMS.

Evaluating the Completeness of TSQL2

Abstract: The question of what is a well-designed temporal data model and query language is a difficult, but also an important one. The consensus temporal query language TSQL2 attempts to take advantage of the accumulated knowledge gained from designing and studying many of the earlier models and languages. In this sense, TSQL2 represents a constructive answer to this question. Others have provided analytical answers by developing criteria, formulated as completeness properties, for what is a good model and language.

The TSQL2 Data Model

Abstract: Adding time to the relational model has been a daunting task [Bolour et al. 1982, McKenzie 1986, Soo 1991, Stam & Snodgrass 1988]. More than two dozen time-extended relational data models have been proposed over the last fifteen years [Snodgrass 1992]. Most of these are valid-time models. Each fact in a valid-time relation has associated the time when it is true in the modeled reality. Other models support transaction-time relations where each fact has associated the time when it is current in the database. A few support both valid and transaction time [Ben-Zvi 1982, BhargavaG such models are termed bitemporal. As a whole, these data models are referred to as temporal data models [Jensen et al. 1994].

An Algebra for TSQL2

Abstract: TSQL2 is a declarative query language, and as such, requires a procedural (algebraic) equivalent for implementation. In this chapter, we describe such an algebraic language. We undertook this design in order to show that TSQL2 can be implemented efficiently, with minimal extension of existing techniques.

Evaluating and Enhancing the Completeness of TSQL2

Abstract: The question of what is a well-designed temporal data model and query language is a di cult, but also an important one. The consensus temporal query language TSQL2 attempts to take advantage of the accumulated knowledge gained from designing and studying many of the earlier models and languages. In this sense, TSQL2 represents a constructive answer to this question. Others have provided analytical answers by developing criteria, formulated as completeness properties, for what is a good model and language. This paper applies important existing completeness notions to TSQL2 in order to evaluate the design of TSQL2. It is shown that TSQL2 satis es only a subset of these completeness notions. In response to this, a minimally modi ed version of TSQL2, termed Applied TSQL2, is proposed; this new language satis es the notions of temporal semi-completeness and completeness which are not satis ed by TSQL2. An outline of the formal semantics for Applied TSQL2 is given. Department of Computer Science University of Arizona Tucson, AZ 85721 fboehlen, rtsg@cs.arizona.edu Department of Mathematics and Computer Science Aalborg University Fredrik Bajers Vej 7E DK{9220 Aalborg , DENMARK csj@iesd.auc.dk Evaluating and Enhancing the Completeness of TSQL2 Copyright c Michael H. Bohlen, Christian S. Jensen and Richard T. Snodgrass 1995

A Second Example

Abstract: This chapter expresses the schema and some of the queries of the extensive consensus test suite for temporal relational query languages [Jensen 1993]. The test suite is not related to performance issues, but has a semantic focus and is intended to be an aid in evaluating the user-friendliness of temporal query languages. An attempt is made to express the schema and queries in TSQL2 in a convenient and natural fashion, as an informal evaluation of that language’s user-friendliness.

Semantics of Time-Varying Attributes and their Use for Temporal Database Design

Abstract: Based on a systematic study of the semantics of temporal attributes of entities, this paper provides new guidelines for the design of temporal relational databases. The notions of observation and update patterns of an attribute capture when the attribute changes value and when the changes are recorded in the database. A lifespan describes when an attribute has a value. And derivation functions describe how the values of an attribute for all times within its lifespan are computed from stored values. The implications for temporal database design of the semantics that may be captured using these concepts are formulated as schema decomposition rules.

Report on the 1995 international workshop on temporal databases

Abstract: This paper provides an overview of the 1995 International Workshop on Temporal Databases. It summarizes the technical papers and related discussions, and three panels: “Wither TSQL3?”, “Temporal Data Management in Financial Applications,” and “Temporal Data Management Infrastructure & Beyond.”

The Surrogate Data Type

Abstract: This chapter introduces the SURROGATE data type, which allows time-varying objects to be modeled.

The From Clause

Abstract: Information retrieval is an integral component of any database management system. Temporal database management systems should offer user-friendly and powerful means of retrieval of data according to temporal criteria. The From clause is an important component of the Select statement: it identifies the underlying relations from which the information is to be retrieved and allows the declaration of range variables. While variables merely serve as “correlation names” (e.g. for joining a table with itself) in SQL-92, TSQL2 variables are designed to increase the temporal expressiveness of the language, in addition to provide “syntactic sugar” in making some queries easier to formulate.

Panel: The State-of-the-Art in Temporal Data Management: Perspectives from the Research and Financial Applications Communities

Abstract: In the first part of the panel, several well-known researchers from the temporal database field discussed ongoing efforts to create an infrastructure to support temporal data management. What infrastructure now exists, or should exist soon?

Valid-Time Selection and Projection

Abstract: Temporal database management systems should offer user-friendly and powerful means of retrieval of data according to temporal criteria. Selection of tuples according to their valid times, which is the times when the information represented by the tuples is valid in the modeled reality [Snodgrass & Ahn 1985], is termed valid-time selection.