NoteCards is a general hypermedia environment designed to help people work with ideas. Its intended users are authors, designers, and other intellectual laborers engaged in analyzing information, designing artifacts, and generally processing ideas. The system provides these users with a variety of hypermedia-based tools for collecting, representing, managing, interrelating, and communicating ideas. This paper presents the NoteCards system as a foil against which to explore some of the major limitations of the current generation of hypermedia systems. In doing so, this paper highlights seven of the major issues that must be addressed in the next generation of hypermedia systems. These seven issues are: search and query, composite nodes, virtual structures, computational engines, versioning, collaborative work, and tailorability. For each of these issues, the papers describes the limitations inherent in NoteCards and the prospects for doing improving the situation in future systems.

This paper attempts to define an object-oriented database system. It describes the main features and characteristics that a system must have to qualify as an objectoriented database system. We have separated these characteristics into three groups: ffl Mandatory, the ones the system must satisfy in order to be termed an objectoriented database system. These are complex objects, object identity, encapsulation, types or classes, inheritance, overriding combined with late binding, extensibility, computational completeness, persistence, secondary storage management, concurrency, recovery and an ad hoc query facility. ffl Optional, the ones that can be added to make the system better, but which are not mandatory. These are multiple inheritance, type checking and inferencing, distribution, design transactions and versions. ffl Open, the points where the designer can make a number of choices. These are the programming paradigm, the representation system, the type system, and uniformity. We...

This paper presents the design and an initial performance evaluation of the query optimizer generator designed for the EXODUS extensible database system. Algebraic transformation rules are translated into an executable query optimizer, which transforms query trees and selects methods for executing operations according to cost functions associated with the methods. The search strategy avoids exhaustive search and it modifies itself to take advantage of past experience. Computational results show that an optimizer generated for a relational system produces access plans almost as good as those produced by exhaustive search, with the search time cut to a small fraction.

With non-traditional application areas such as engineering design, image/voice data management, scientific/statistical applications, and artificial intelligence systems all clamoring for ways to store and efficiently process larger and larger volumes of data, it is clear that traditional database technology has been pushed to its lim-its. It also seems clear that no single database system will be capable of simultaneously meeting the functionality and performance requirements of such a diverse set of applications. In this paper we describe the initial design of EXODUS, an extensible database system that will facilitate the fast development of high-performance, application-specific database systems. EXODUS provides certain kernel facilities, including a versatile storage manager and a type manager. In addition, it provides an architectural framework for building application-specific database sys-tems, tools to partially automate the generation of such systems, and libraries of software components (e.g., access methods) that are likely to be useful for many application domains.

The need to examine data structures often occurs in programming language and database management systems. In this paper we describe how a browser for a strongly typed programming language ( PS-algol ) may be written in a type secure manner in a closed persistent environment. This is achieved without resorting to magic or having to break the type rules of the language by exploiting a compiler that is a object with full civil rights in the environment. The use of impact of such an object is discussed. Safe Browsing in a Strongly Typed Persistent Environment Page 3 Introduction A mechanism to display data structures is often required in database and programming language systems. Usually this requirement is satisfied by a tool known as a browser. Browsers are used extensively to traverse through the data structures found in database systems often to gain insight into how a complex and highly dynamic system is behaving. They are also of great use in debugging and, if powerful enough, can...

This thesis presents research into the construction of persistent programming systems. Much of the thesis is concerned with the design and implementation of persistent programming languages, in particular PS-algol and Napier. Both languages support machine independent vector and raster graphics data types. Napier provides an environment mechanism that enables the incremental construction and binding of programs. Napier has a powerful type system featuring parametric polymorphism and abstract data types. The machine supporting Napier, the Persistent Abstract Machine, is investigated. The machine supports an efficient implementation of parametric polymorphism and abstract data types. The Persistent Abstract Machine has a layered architecture in which permits experimentation into language implementation and store design. The construction of compilers in a persistent environment is explored. A flexible compiler architecture is developed. With it, a family of compilers may be constructed a...

Object-oriented programming has recently emerged as one of the most important programming paradigms. While object-oriented programming clearly owes an intellectual debt to AI, it appears to be displacing some AI techniques, such as rule-based programming, from the marketplace. This need not be so as pathbased rules---forward-chaining production rules that are restricted to follow pointers between objects---fit into the object-oriented paradigm in a clean and elegant way. The combination of path-based rules and object-oriented programming should be useful in AI applications, and in the more general problem of transferring AI techniques to the larger computer science community.

Object-oriented data models organize objects according to common properties into classes. Similarly, some object-oriented systems organize classes into metaclasses which define common properties of their class instances. But in none of them metaclasses can be used to define common properties of instances of their instances. Metaclasses in VODAK, a distributed object-oriented database system developed at IPSI, have been extended in that direction. They can be employed to predefine a common structure and behavior of classes and of individual objects at the metaclass level. Using this feature, metaclasses can be employed to introduce new data model primitives, and thus, to extend the VODAK kernel model with capabilities needed in specific application domains. We illustrate the use of metaclasses in database integration. A frequent approach to integrate a set of related classes is to define a generalization class for them. Class definition by generalization, however, is usually not supported by ordinary data models. It is left to the application developer to define the semantics of generalization classes with every single generalization class. Using metaclasses the semantics of generalization classes can be defined once and for all at the metaclass level.

User interface toolkits and higher-level tools built on top of them play an ever increasing part in developing graphical user interfaces. This paper describes the Xit system, a user interface development tool for the X Window System, based on Common Lisp, comprising user interface toolkits as well as high-level interactive tools organized into a layered architecture. We especially focus on the object-oriented design of the lowerlevel toolkits and show how advanced features for describing automatic screen layout, visual feedback, application links, complex interaction, and dialog control, usually not included in traditional user interface toolkits, are integrated. Keywords: User interface toolkits, user interface development tools, graphical user interfaces, interaction techniques, object-oriented programming Introduction Today, graphical user interfaces are mostly built with the help of user interface toolkits or, recently, high-level interactive tools built on top of them [15]. Ove...

Object-oriented programming has recently emerged as one of the most important programming paradigms. While object-oriented programming clearly owes an intellectual debt to AI, it appears to be displacing some AI techniques, such as rule-based programming, from the marketplace. This need not be so as pathbased rules---forward-chaining production rules that are restricted to follow pointers between objects---fit into the object-oriented paradigm in a clean and elegant way. The combination of path-based rules and object-oriented programming should be useful in AI applications, and in the more general problem of transferring AI techniques to the larger computer science community. To this day, forward-chaining production rules remain largely unused in mainstream object-oriented applications. One reason for this lack of use is, of course, that many production rule systems (such as most versions of OPS (Cooper & Wogrin 1988), etc.) are written in LISP, and not in a major object-...