This glossary contains concepts specific to temporal databases that are well-defined, well understood, and widely used. In addition to defining and naming the concepts, the glossary also explains the decisions made. It lists competing alternatives and discusses the pros and cons of these. It also includes evaluation criteria for the naming of concepts. This paper is a structured presentation of the results of e-mail discussions initiated during the preparation of the first book on temporal databases, Temporal Databases: Theory, Design, and Implementation, published by Benjamin/Cummings, to appear January 1993. Independently of the book, an initiative aimed at designing a consensus Temporal SQL is under way. The paper is a contribution towards establishing common terminology, an initial subtask of this initiative. This paper appeared in SIGMOD Record, Vol. 21, No. 3, September 1992. 1 Introduction Maintaining a precise, well-defined, and intuitive technical language is important to t...

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...

This paper describes our ongoing work developing the Stanford Stream Data Manager (STREAM), a system for executing continuous queries over multiple continuous data streams. The STREAM system supports a declarative query language, and it copes with high data rates and query workloads by providing approximate answers when resources are limited. This paper describes specific contributions made so far and enumerates our next steps in developing a general-purpose Data Stream Management System.

Semistructured data may be irregular and incomplete and does not necessarily conform to a fixed schema. As with structured data, it is often desirable to maintain a history of changes to data, and to query over both the data and the changes. Representing and querying changes in semistructured data is more difficult than in structured data due to the irregularity and lack of schema. We present a model for representing changes in semistructured data and a language for querying over these changes. An important feature of our approach is that we represent and query changes directly as annotationson the affected data, instead of indirectly as the difference between database states. We describe the implementation of our model and query language. We also describe the design and implementation of a query subscription service that permits users to subscribe to changes in semistructured information sources. 1

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This paper describes our ongoing work developing the Stanford Stream Data Manager (STREAM), a system for executing continuous queries over multiple continuous data streams. The STREAM system supports a declarative query language, and it copes with high data rates and query workloads by providing approximate answers when resources are limited. This paper describes specific contributions made so far and enumerates our next steps in developing a general-purpose Data Stream Management System.

It seems somehow fitting to begin this paper on databases that store historical information with a chronology, touching briefly on all work that I am aware of in this area. I discuss in some detail what I consider to be the ten most important papers and events in terms of their impact on the discipline of temporal databases. These are emphatically not meant to detract from the other excellent papers in temporal databases. My goal is to characterize the evolution of this field, as an introduction to the approximately 350 papers specifically relating time to databases that have appeared thus fax. I then identify and discuss areas where more work is needed. 1

This paper presents the model which is the basis for a system to manage various kinds of sequence data. The model separates the data from the ordering information, and includes operators based on two distinct abstractions of a sequence. The main contributions of the model are: (a) it can deal with different types of sequence data, (b) it supports an expressive range of sequence queries, (c) it draws from many of the diverse existing approaches to modeling sequence data. 1

Many applications require the ability to manipulate sequences of data. We motivate the importance of sequence query processing, and present a framework for the optimization of sequence queries based on several novel techniques. These include query transformations, optimizations that utilize meta--data, and caching of intermediate results. We present a bottom-up algorithm that generates an efficient query evaluation plan based on cost estimates. This work also identifies a number of directions in which future research can be directed. 1 Introduction Many real life applications manipulate data that is inherently sequential. Such data is logically viewed and queried in terms of a sequence abstraction and is often physically stored as a sequence. Databases should (a) allow sequences to be queried in a declarative manner, utilizing the ordered semantics of the data, and (b) take advantage of the opportunities available for query optimization. Relational databases are inadequate in this re...

The relational algebra is a procedural query language for relational databases. In this paper we survey extensions of the relational algebra that can query databases recording time-varying data. Such an algebra is a critical part of a temporal DBMS. We identify 26 criteria that provide an objective basis for evaluating temporal algebras, Seven of the criteria are shown to be mutually unsatisfiable, implying there can be no perfect temporal algebra, Choices made as to which of the incompatible criteria are satisfied characterize existing algebras Twelve time-oriented algebras are summarized and then evaluated against the criteria. We demonstrate that the design space has in some sense been explored in that all combinations of basic design decisions have at least one representative algebra. Coverage of the remaining criteria provides one measure of the quality of each algebra We argue that all of the criteria are independent and that the criteria identified as compatible are indeed so, Finally, we list plausible properties proposed by others that are either subsumed by other criteria, are not well defined, or have no objective basis for being evaluated. The algebras realize many different approaches to what appears initially to be a straightforward design task.