A temporal database contains time-varying data. In a real-time database transactions have deadlines or timing constraints. In this paper we review the substantial research in these two heretofore separate research areas. We first characterize the time domain, then investigate temporal and real-time data models. We evaluate temporal and real-time query languages along several dimensions. Temporal and real-time DBMS implementation is examined. We conclude with a summary of the major accomplishments of the research to date, and list several research questions that should be addressed next. Keywords: object-oriented database, relational databases, query language, temporal data model, time-constrained database, transaction time, user-defined time, valid time 1 Introduction Time is an important aspect of all real-world phenomena. Events occur at specific points in time; objects and the relationships among objects exist over time. The ability to model this temporal dimension of the real worl...

: In certain areas of artificial intelligence there is need to represent continuous change and to make statements that are interpreted with respect to time intervals rather than time points. To this end we develop a modal temporal logic based on time intervals, a logic which can be viewed as a generalization of pointbased modal temporal logic. We discuss related logics, give an intuitive presentation of the new logic, and define its formal syntax and semantics. We make no assumption about the underlying nature of time, allowing it to be discrete (such as the natural numbers) or continuous (such as the rationals or the reals), linear or branching, complete (such as the reals) or not (such as the rationals). We show, however, that there are formulas in the logic that allow us to distinguish all these situations. We also give a translation of our logic into first-order logic, which allows us to apply some results on first-order logic to our modal one. Finally, we consider the difficulty o...

We define formal notions of temporal domain and temporal database, and use them to survey a wide spectrum of temporal query languages. We distinguish between an abstract temporal database and its concrete representations, and accordingly between abstract and concrete temporal query languages. We also address the issue of incomplete temporal information. 1 Introduction A temporal database is a repository of temporal information. A temporal query language is any query language for temporal databases. In this paper we propose a formal notion of temporal database and use this notion in surveying a wide spectrum of temporal query languages. The need to store temporal information arises in many computer applications. Consider, for example, records of various kinds: financial [37], personnel, medical [98], or judicial. Also, monitoring data, e.g., in telecommunications network management [4] or process control, has often a temporal dimension. There has been a lot of research in temporal dat...

In valid-time indeterminacy it is known that an event stored in a database did in fact occur, but it is not known exactly when. In this paper we extend the SQL data model and query language to support valid-time indeterminacy. We represent the occurrence time of an event with a set of possible instants, delimiting when the event might have occurred, and a probability distribution over that set. We also describe query language constructs to retrieve information in the presence of indeterminacy. These constructs enable users to specify their credibility in the underlying data and their plausibility in the relationships among that data. A denotational semantics for SQL’s select statement with optional credibility and plausibility constructs is given. We show that this semantics is reliable, in that it never produces incorrect information, is maximal, in that if it were extended to be more informative, the results may not be reliable, and reduces to the previous semantics when there is no indeterminacy. Although the extended data model and query language provide needed modeling capabilities, these extensions appear initially to carry a significant execution cost. A contribution of this paper is to demonstrate that our approach is useful and practical. An efficient representation of valid-time indeterminacy and efficient query processing algorithms are provided. The cost of

Reasoning about one's personal schedule of appointments is a common but surprisingly complex activity. Motivated by the novel application of planning and temporal reasoning techniques to this problem, we have extended the formalization of the temporal distance model of Dechter, Meiri, and Pearl. We have developed methods for using dates as reference intervals and for meeting the challenge of repeated activities, such as weekly recurring appointments. Introduction Intelligently managing a busy personal schedule is not an easy task, but it is a ubiquitous one. The benefit to be derived from an automated facility for maintaining an appointment calendar---with all of the complex constraint management that that entails 1 ---is potentially enormous. In the context of CLASM, 2 an intelligent appointment manager, we have begun to explore the utility of AI methods for maintaining a library of complex activity descriptions, verifying whether an activity is possible, and checking the cons...

. This chapter introduces a new approach to temporal extensions of SQL. The main difference from most of the current proposals is the use single time points, rather than intervals or various other complexvalues for references to time, while still achieving efficient query evaluation. The proposed language, SQL/TP, extends the syntax of SQL/92 to handle temporal data in a natural way: it adds a single data type to represent a linearly ordered universe of time instants. The semantics of the new language naturally extends the standard SQL semantics and eliminates or fixes many of the problems connected with defining a precise semantics to temporal query languages based on explicit interval-valued temporal attributes. The efficient query evaluation procedure is based on a compilation technique that translates SQL/TP queries to SQL/92. Therefore existing off-shelf database systems can be used as back-ends for implementations based on this approach to manage temporal data. 1 Why another temp...

. Motivation is given for the construction of an absolutely complete theory of spatial regions. Additional axioms for the RCC theory (Randell, Cui and Cohn 1992) are suggested to restrict the class of models satisfying this theory. Specific problems addressed are the characterisation of dimension and the provision of adequate existential axioms. 1 Introduction Spatial information is essential to a broad spectrum of knowledge domains and to many important reasoning tasks. Hence, an ontology of space and spatial regions is fundamental to the development of representations and reasoning mechanisms for AI systems. Geometry and Topology are both highly developed fields of mathematics. In both areas, the formal theories developed take points (or in the case of incidence geometry, points and lines) as primitive elements from which objects corresponding to regions are constructed set-theoretically. From the point of view of knowledge representation and automated reasoning this often lea...

The development of any comprehensive proposal for spatio-temporal databases involves significant extensions to many aspects of a non-spatio-temporal architecture. One aspect that has received less attention than most is the development of a query calculus that can be used to provide a semantics for spatio-temporal queries and underpin an effective query optimization and evaluation framework. In this paper, we show how a query calculus for spatiotemporal object databases that builds upon the monoid calculus proposed by Fegaras and Maier for ODMG-compliant database systems can be developed. The paper shows how an extension of the ODMG type system with spatial and temporal types can be accommodated into the monoid approach. It uses several queries over historical (possibly spatial) data to illustrate how, by mapping them into monoid comprehensions, the way is open for the application of a logical optimizer based on the normalization algorithm proposed by Fegaras and Maier.

In historical indeterminacy, it is known that an event stored in a temporal database did in fact occur, but it is not known exactly when the event occurred. We present the possible tuples data model, in which each indeterminate event is represented with a set of possible events that delimits when the event might have occurred, and a probability distribution over that set. We extend the TQuel query language with constructs that specify the user's credibility in the underlying historical data and in the user's plausibility in the relationships among that data. We provide a formal tuple calculus semantics, and show that this semantics reduces to the determinate semantics. We outline an efficient representation of historical indeterminacy, and efficient query processing algorithms, demonstrating the practicality of our proposed approach. 1 Department of Computer Science University of Arizona Tucson, AZ 85721 fcurtis,rtsg@cs.arizona.edu Historical Indeterminacy 1 Copyright c...

The W3C’s Semantic Web Activity is illustrating the use of semantics for information integration, search, and analysis. However, the majority of the work in this community has focused more on the thematic aspects of information and has paid less attention to its spatial and temporal dimensions. In this paper, we present an integrative ontology-based framework incorporating the thematic, spatial, and temporal dimensions of information. This framework is built around the RDF metadata model. Our ultimate goal is to provide an information system which allows searching and analysis of relationships in any or all of the three dimensions of space, time, and theme. Toward this end, we present an upper-level ontology combining concepts and relationships from both the thematic and spatial dimensions and show how to incorporate temporal semantics into this ontology. We also introduce the notion of a thematic context linking entities of differing dimensions and define a set of query operators built upon these contexts.