Navigational accesses in a temporal object model

Computing Research Repository, 2011

Many works have focused, for over twenty five years, on the integration of the time dimension in databases (DB). However, the standard SQL3 does not yet allow easy definition, manipulation and querying of temporal DBs. In this paper, we study how we can simplify querying and manipulating temporal facts in SQL3, using a model that integrates time in a native manner. To do this, we propose new keywords and syntax to define different temporal versions for many relational operators and functions used in SQL. It then becomes possible to perform various queries and updates appropriate to temporal facts. We illustrate the use of these proposals on many examples from a real application.

Information Systems, 1990

Temporal databases maintain not only current data of an enterprise but also the history of evolution for the current data (i.e. temporal data). In order to access an object from temporal databases, query languages should have facilities of specifying time. A11 users will use not only ubsolute rime (e.g. My 1987) but also ubsrract time (or relative time) (e.g. last summer) for specifying the time that an event occurred. In this paper, we designed an extended temporal query language (ETQL) which supports both absolute time and abstract time specification. An introduction of the abstract time concept in the temporal query language provides users with friendliness and easiness in specifying time. The ETQL was implemented as front-end system on INGRES DBMS running under the 4.2BSD UNIX system.

Systems and Computers in Japan, 1999

A path expression in object-oriented databases is an accepted means of navigating over database objects. A backward navigation in a path expression is an operation to find the objects that have a given target object as a given property value. A path expression pd is called possible with respect to a class C if there is a database that contains a path satisfying the following conditions: 1. The path starts from an object in C. 2. The sequence of the properties on the path coincides with pd. In this paper, we first present a sound and complete axiomatization for computing a path expression that is possible with respect to a class. Then we present a polynomial-time algorithm that decides whether a path expression is possible with respect to a class.

2001

Abstract Managing and relating temporal information at different time units is an important issue in many applications and research areas, among them temporal object-oriented databases. Due to the semantic richness of the object-oriented data model, the introduction of multiple temporal granularities in such a model poses several interesting issues. In particular, object-oriented query languages provide a navigational approach to data access, performed via path expressions.

1998

Abstract Most database research on modeling time has concentrated on the definition of a particular temporal model and its incorporation into a (relational or object) database management system. This has resulted in quite a large number of different temporal models, each providing a specific set of temporal features. This paper presents an object-oriented framework for temporal models which supports multiple notions of time.

Statistical and Scientific Database Management, 1988

In previous work, we introduced a data model and a query language for temporal data. The model was designed independently of any existing data model rather than an extension of one. This approach provided an insight into the special requirements for handling temporal data. In this paper, we discuss the implications of supporting such a model in the relational database

does not yet allow easy definition, manipulation and querying of temporal DBs. In this paper, we study how we can simplify querying and manipulating temporal facts in SQL3, using a model that integrates time in a native manner. To do this, we propose new keywords and syntax to define different temporal versions for many relational operators and functions used in SQL. It then becomes possible to perform various queries and updates appropriate to temporal facts. We illustrate the use of these proposals on many examples from a real application.

1997

Any software made available via TIMECENTER is provided "as is" and without any express or implied warranties, including, without limitation, the implied warranty of merchantability and fitness for a particular purpose.

Proceedings of the 16th International …, 1990

In this paper, we describe a new indexing technique, the time indez, for improving the performance of certain classes of temporal queries. The time index can be used to retrieve versions of objects that are valid during a specific time period. It supports the processing of the temporal WHEN operator and temporal aggregate functions efficiently. The time indexing scheme is also extended to improve the performance of the temporal SELECT operator, which retrieves objects that satisfy a certain condition during a specific time period. We will describe the indexing technique, and its search and insertion algorithms. We also describe an algorithm for processing a commonly used temporal JOIN operation. Some results of a simulation for comparing the performance of the time index with other proposed temporal access structures are presented.

Eprint Arxiv 1002 1143, 2010

Time is one of the most difficult aspects to handle in real world applications such as database systems. Relational database management systems proposed by Codd offer very little built-in query language support for temporal data management. The model itself incorporates neither the concept of time nor any theory of temporal semantics. Many temporal extensions of the relational model have been proposed and some of them are also implemented. This paper offers a brief introduction to temporal database research. We propose a conceptual model for handling time varying attributes in the relational database model with minimal temporal attributes.

Proceedings of the sixteenth ACM conference on Conference on information and knowledge management - CIKM '07, 2007

Database and Expert Systems Applications, 1992

This paper introduces a temporal relational algebra as a query language for temporal deductive databases, i.e., Temporal Datalog programs. In Temporal Datalog programs, temporal relationships among data are formalized through temporal operators, not by an explicit reference to time. The minimum model of a given Temporal Datalog program is regarded as the temporal database the program models intensionally. Users query temporal deductive databases using a temporal relational algebra (TRA), which is a pointwise extension of the relational algebra. During the evaluation of TRA expressions, portions of temporal relations are retrieved from a given temporal deductive database when needed. Bottom-up evaluation strategies such as the fixed-point computation can be used to compute portions of temporal relations over intervals. An extension of Temporal Datalog with generic modules is also proposed. Through modules, temporal relations created during the evaluation of TRA expressions may be fed back to the deductive part for further manipulation.

1998

Most of the database research on modeling time has concentrated on the definition of a particular temporal model and its incorporation into a (relational or object) database management system. This has resulted in quite a large number of different temporal models, each providing a specific set of temporal features. Therefore, the first step of this work is a design space for temporal models which accommodates multiple notions of time, thereby classifying design alternatives for temporal models.

1999

This document outlines a specification for a temporal query system called Chronus II. The design of Chronus II has been influenced by the original Chronus system, which was written in Stanford University by Amar Das, and by the TSQL2 temporal query specification, which was written by Richard Snodgrass at the University of Arizona.

Dozens of temporal extension of the relational data model and of the query language SQL have appeared in recent years. Recently, a committee formed by researchers from the academic and the industrial worlds designed a consensual extension of the SQL-92 standard to include time, epitomized as TSQL2.