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An electronic book may be viewed as an application with a multimedia database. We define an electronic textbook as an electronic book that is used in conjunction with instructional resources such as lectures. In this paper, we propose an electronic textbook data model with topics, topic sources, metalinks (relationships among topics), and instructional modules which are multimedia presentations possibly capturing real-life lectures of instructors. Using the data model, the system provides users a topic-guided multimedia lesson construction. This paper concentrates, in detail, on the use of one metalink type in lesson construction, namely, prerequisite dependencies, and provides a sound and complete axiomatization of prerequisite dependencies. We present a simple automated way of constructing lessons for users where the user lists a set of topic names (s)he is interested in, and the system automatically constructs and delivers the 'best' user-tailored lesson as a multimedia presentation, where 'best' is characterized in terms of both topic closures with respect to prerequisite dependencies and what the user knows about topics. We model and present sample lesson construction requests for users, discuss their complexity, and give algorithms that evaluate such requests. For expensive lesson construction requests, we list heuristics and empirically evaluate their performance. We also discuss the worst-case performance guarantees of lesson request algorithms. Index Terms--Electronic textbooks, electronic textbook data models, instructional modules, topics, lesson construction, lesson construction heuristics, lesson complexity.

This paper describes VISUAL, a graphical icon-based query language with a user-friendly graphical user interface for scientific databases and its query processing techniques. VISUAL is suitable for domains where visualization of the relationships is important for the domain scientist to express queries. In VISUAL, graphical objects are not tied to the underlying formalism; instead, they represent the relationships of the application domain. VISUAL supports relational, nested, and object-oriented models naturally and has formal basis. For ease of understanding and for efficiency reasons, two VISUAL semantics are introduced, namely, the interpretation and execution semantics. Translations from VISUAL to the Object Query Language (for portability considerations) and to an object algebra (for query processing purposes) are presented. Concepts of external and internal queries are developed as modularization tools. Index Terms--Database query languages, query processing, scientific databases, object algebra.

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 previously separate areas. First we characterize the time domain; then we investigate temporal and real-time data models. We evaluate temporal and real-time query languages along several dimensions. We examine temporal and real-time DBMS implementation. Finally, we summarize major research accomplishments to date and list several unanswered research questions. Index Terms - Object-oriented databases, relational databases, query languages, temporal data models, time-constrained databases, transaction time, user-defined time, valid time.

We consider the problem of choosing a storage model for a nested relation (i.e., a relation containing relations). We introduce a technique that uses the workload information of the database system under consideration to obtain a 'better' storage model (i.e., one with a lower query cost) for a given nested relation. The nested relation scheme is first represented as a tree called the scheme tree. By using the workload information and by performing a series of merges in the nodes of the scheme tree, a near-optimum scheme tree is produced, and file organization types are assigned to each node (file) in the scheme tree. We apply our methodology by using a specific nested relational algebra and three file organization types, namely, sequential, heap, and dense index files. However, the methodology can be used with other nested relational algebra languages and other file organization types. In all of our experiments, the proposed methodology has located the optimum storage model and the optimum file organization techniques for the external and internal relations of the tested nested relations.

In this paper, we utilize intervals for unknown values in incomplete relational databases. We use tables to represent unknown relations. First, we define three partial tuple types in a table to specify incompleteness relationships among tuples of the same table. For tuples of different tables, we distinguish between the cases where incompleteness is introduced at the relation level, tuple level, or attribute value level. Also, based on these relationships among tuples in different tables, we present a family of incomplete relational database models. For each of the models, we show that query evaluation is sound (i.e., no incorrect results are derivable) in the Imielinski-Lipski sense. None of the models is complete (i.e., all valid conclusions are derivable) in the Imielinski-Lipski sense. We briefly compare two of the models in the family with other approaches. Considering each table tuple as a set of d-dimensional cubes, each model in the family of models presented in this paper can be considered and implemented as a geometric database model. We briefly summarize the geometric operations and the primitive update semantics that need to be utilized in such an implementation.

In this paper, we consider the problem of querying multimedia presentations based on content information. We believe that presentations should become an integral part of multimedia database systems and users should be able to store, query, and, possibly, manipulate multimedia presentations using a single database management system software. Multimedia presentations are modeled as presentation graphs, which are directed acyclic graphs that visually specify multimedia presentations. Each node of a presentation graph represents a media stream. Edges depict sequential or concurrent playout of streams during the presentation. Information captured in each individual stream and the presentation order of streams constitute the content information of the presentation. Querying multimedia presentation graphs based on content is important for the retrieval of information from a database. We present a graph data model for the specification of multimedia presentations and discuss query languages as effective tools to query and manipulate multimedia presentation graphs with respect to content information. To query the information flow throughout a multimedia presentation, as well as in each individual multimedia stream, we use revised versions of temporal operators Next, Connected, and Until, together with path formulas. These constructs allow us to specify and query paths along a presentation graph. We present an icon-based, graphical query language, GVISUAL, that provides iconic representations for these constructs and a user-friendly graphical interface for query specification. We also present an OQL-like language, GOQL (Graph OQL), with similar constructs, that allows textual and more traditional specifications of graph queries. Finally, we introduce GCalculus (Graph Calculus), a calculus-based language that establishes the formal grounds for the use of temporal operators in path formulas and for querying presentation graphs with respect to content information. We also discuss GCalculus/S (GCalculus with sets) which avoids highly complex query expressions by eliminating universal path quantifier, the negation operator, and the universal quantifier. GCalculus/S represents the formal basis for GVISUAL, i.e., GVISUAL uses the constructs of GCalculus/S directly. Index Terms - Multimedia databases, graphical query languages, multimedia presentation.