FORMAL SEMANTICS FOR TIME IN DATABASES

The concept of an historical database is introduced as a tool for modelling the dynamic nature of some part of the real world. Just as first-order logic has been shown to be a useful formalism for expressing and understanding the underlying semantics of the relational database model, intensional logic is presented as an analogous formalism for expressing and understanding the temporal semantics involved in an historical database. The various components of the relational model, as extended to include historical relations, are discussed in terms of the model theory for the logic ILs, a variation of the logic IL formulated by Richard Montague. The modal concepts of intensional and extensional data constraints and queries are introduced and contrasted. Finally, the potential application of these ideas to the problem of Natural Language Database Querying is discussed.Information Systems Working Papers Serie

OBJECTS IN TIME

Two recent lines of database research, proceeding independently, have been concerned with providing a richer, more intuitive view of information at the user level. Historical database research has focused on ways to provide users with a view of information anchored and evolving in the temporal dimension. Object-oriented database research focuses on encapsulating both the structure and the behavior of the objects that users intend to model. In this paper we explore how these two lines of research might be brought together, providing to the user the representation and management of objects in time.Information Systems Working Papers Serie

Schema Vacuuming in Temporal Databases

Temporal databases facilitate the support of historical information by providing functions for indicating the intervals during which a tuple was applicable (along one or more temporal dimensions). Because data are never deleted, only superceded, temporal databases are inherently append-only resulting, over time, in a large historical sequence of database states. Data vacuuming in temporal databases allows for this sequence to be shortened by strategically, and irrevocably, deleting obsolete data. Schema versioning allows users to maintain a history of database schemata without compromising the semantics of the data or the ability to view data through historical schemata. While the techniques required for data vacuuming in temporal databases have been relatively well covered, the associated area of vacuuming schemata has received less attention. This paper discusses this issue and proposes a mechanism that fits well with existing methods for data vacuuming and schema versioning

ON THE EXPRESSIVE POWER OF INFINITE TEMPORAL DATABASES

We discuss different techniques for representing infinite temporal data. There are two basic approaches: A procedural description, as used in production systems, and represented, in this paper, by a version of Datalog. The second approach is a more declarative method, using some form of temporal logic programming. We examine several versions of each approach, and compare their expressive power, i.e., what temporal data each formalism can capture.Information Systems Working Papers Serie

A DATABASE ARCHITECTURE FOR SUPPORTING BUSINESS TRANSACTIONS

The central hypothesis of this paper is that database design and systems design in general can be simplified considerably by tailoring the design methods to a suitable range of applications. Domain-specific knowledge can be incorporated into a specialized database architecture that leaves the designer with the task to specify only the application-specific parts. Based on an analysis of business constraints, we propose such an architecture for the domain of business transaction processing. The architecture offers several data and transaction management services, special-purpose sub-databases, and design checking rules to be used by the application designer. Two services, input management and audit and control services, are described in more detail.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

Partial Computation in Real-Time Database Systems: A Research Plan

State-of-the-art database management systems are inappropriate for real-time applications due to their lack of speed and predictability of response. To combat these problems, the scheduler needs to be able to take advantage of the vast quantity of semantic and timing information that is typically available in such systems. Furthermore, to improve predictability of response, the system should be capable of providing a partial, but correct, response in a timely manner. We therefore propose to develop a semantics for real-time database systems that incorporates temporal knowledge of data-objects, their validity, and computation using their values. This temporal knowledge should include not just historical information but future knowledge of when to expect values to appear. This semantics will be used to develop a notion of approximate or partial computation, and to develop schedulers appropriate for real-time transactions