THE HISTORICAL RELATIONAL DATA MODEL (HRDM) AND ALGEBRA BASED ON LIFESPANS

Critical to the design of an historical database model is the representation of the âexistenceâ of objects across the temporal dimension -- for example, the "birth," "death," or "rebirth" of an individual, or the establishment or dis-establishment of a relationship. The notion of the "lifespan" of a database object is proposed as a simple framework for expressing these concepts. An object's lifespan is simply those periods of time during which the database models the properties of that object. In this paper we propose the historical relational data model (HRDM) and algebra that is based upon lifespans and that views the values of all attributes as functions from time points to simple domains. The model that we obtain is a consistent extension of the relational data model, and provides a simple mechanism for providing both time-varying data and time-varying schemes.Information Systems Working Papers Serie

THE HISTORICAL RELATIONAL DATA MODEL (HRDM) AND ALGEBRA BASED ON LIFESPANS

Critical to the design of an historical database model is the representation of the âexistenceâ of objects across the temporal dimension -- for example, the "birth," "death," or "rebirth" of an individual, or the establishment or dis-establishment of a relationship. The notion of the "lifespan" of a database object is proposed as a simple framework for expressing these concepts. An object's lifespan is simply those periods of time during which the database models the properties of that object. In this paper we propose the historical relational data model (HRDM) and algebra that is based upon lifespans and that views the values of all attributes as functions from time points to simple domains. The model that we obtain is a consistent extension of the relational data model, and provides a simple mechanism for providing both time-varying data and time-varying schemes.Information Systems Working Papers Serie

A SIMPLE, GENERAL STRUCTURE FOR TEMPORAL DOMAINS

Much recent research has focused on .the need for, and definitions of, historical (or temporal) database and information systems to serve expanding information needs in a variety of applications. Almost all of this research has assumed that the domain of time itself was well-understood, and some representation for it simply needed to be included in the model to provide the needed temporal dimension. In this paper we present a simple, set-theoretic structure for a time domain which is independent of any particular calendric system. We concentrate on the general structure and operations necessary to support the needs arising in modelling time in information systems.Information Systems Working Papers Serie

ON CONSISTENT EXTENSIONS TO THE RELATIONAL DATABASE MODEL

Information Systems Working Papers Serie

ON CONSISTENT EXTENSIONS TO THE RELATIONAL DATABASE MODEL

Information Systems Working Papers Serie

ON COMPLETENESS OF HISTORICAL RELATIONAL DATA MODELS

Several proposals for extending the relational data model to incorporate the temporal dimension of data have appeared in the past several years. These proposals have differed considerably in the way that the temporal dimension has been incorporated both into the structure of the extended relations that are defined as part of these extended model, and into the operations of the extended relational algebra or calculus component of the models. Because of these differences it has been difficult to compare the proposed models and to make judgements as to which of them is "better" or indeed, the "best." In this paper we propose a notion of historical relational completeness, analogous to Codd's notion of relational completeness, and examine several historical relational proposals in light of this standard.Information Systems Working Papers Serie

ON THE SEMANTICS OF TRANSACTION TIME AND VALID TIME IN BITEMPORAL DATABASES

Numerous proposals for extending the relational data model to incorporate the temporal dimension of data have appeared in the past several years. While most of these have been historical databases, incorporating in some fashion a valid time dimension to the data model and the query languages, others have been rollback databases, incorporating a transaction time dimension, or bitemporal databases, incorporating both of these temporal dimensions. In this paper we address an issue that has been lacking in many of these papers, namely, a formal specification of the precise semantics of these temporal dimensions of data. We introduce the notion of reference time - the time that any operation is applied to the database state - and provide a logical analysis of the interrelationships among these three temporal dimensions. We also provide an analysis of the meaning of various variables such as now and â which have been used in many of these models without a complete specification of their semantics.Information Systems Working Papers Serie

NATURAL LANGUAGE QUERYING OF HISTORICAL DATABASES -- THE QE-III LANGUAGE DEFINITION AND EXAMPLES

Information Systems Working Papers Serie

THE DECLINING PRICE PARADOX OF NEW TECHNOLOGIES

The declining prices of new technology products often results in a tendency for many decision makers to wait for lower prices, and to postpone a capital investment. This paper makes a distinction between the prices of technology elements and the prices of components and systems. There are many cases where the price reduction over time applies only to some elements of the system, while the total price of the improved system remains almost the same. For those cases, a DECLINING PRICE PARADOX is spelled out. The Paradox suggests that the more the price of the investment is subject to future reduction, the more urgent it is to invest in this technology. The paper incorporates learning considerations in the investment decision making, and states the conditions where the paradox applies.Information Systems Working Papers Serie