Mayer D. Schwartz

The Dexter hypertext reference model

This paper presents the Dexter hypertext reference model. The Dexter model is an attempt to capture, both formally and informally, the important abstractions found in a wide range of existing and future hypertext systems. The goal of the model is to provide a principled basis for comparing systems as well as for developing interchange and interoperability standards. The model is divided into three layers. The storage layer describes the network of nodes and links that is the essence of hypertext. The runtime layer describes mechanisms supporting the user’s interaction with the hypertext. The within-component layer covers the content and structures within hypertext nodes. The focus of the model is on the storage layer as well as on the mechanisms of anchoring and presentation specification that form the interfaces between the storage layer and the within-component and runtime layers, respectively. The model is formalized in the specification language Z, a specification language based on set theory. The paper briefly discusses the issues involved in comparing the characteristics of existing systems against the model.

Neptune: a hypertext system for CAD applications

Even though many of the essential notions of hypertext were first contained in the description of a “memex,” written by Vannevar Bush in 1945 [Bus45], there are today only a few scattered implementations of hypertext, let alone any serious use of it in a CAD environment. In what follows, we describe what hypertext is all about. We describe a prototype hypertext system, named Neptune, that we have built. We show how it is useful, especially its broad applicability to CAD.

The tracker: a threat to statistical database security

The query programs of certain databases report raw statistics for query sets, which are groups of records specified implicitly by a characteristic formula. The raw statistics include query set size and sums of powers of values in the query set. Many users and designers believe that the individual records will remain confidential as long as query programs refuse to report the statistics of query sets which are too small. It is shown that the compromise of small query sets can in fact almost always be accomplished with the help of characteristic formulas called trackers. Schlörers individual tracker is reviewed; it is derived from known characteristics of a given individual and permits deducing additional characteristics he may have. The general tracker is introduced: It permits calculating statistics for arbitrary query sets, without requiring preknowledge of anything in the database. General trackers always exist if there are enough distinguishable classes of individuals in the database, in which case the trackers have a simple form. Almost all databases have a general tracker, and general trackers are almost always easy to find. Security is not guaranteed by the lack of a general tracker.

Contexts—a partitioning concept for hypertext

Hypertext systems provide good information management support for a wide variety of documentation efforts. These efforts range from developing software to writing a book. However, existing hypertext systems provide poor support for collaboration among teams of authors. This paper starts by briefly describing properties of several existing hypertext systems. Then several models for forming partitions in a hypertext database are examined and contexts, a partitioning scheme that supports multiperson cooperative efforts, are introduced. The semantic issues involved in defining contexts are explored in detail.

Viewing a programming environment as a single tool

Programming environments support the creation, modification, execution and debugging of programs. The goal of integrating a programming environment is more than simply building tools that share a common data base and provide a consistent user interface. Ideally, the programming environment appears to the programmer as a single tool; there are no firewalls separating the various functions provided by the environment. This paper describes the techniques used to integrate Magpie, an interactive programming environment for Pascal. Display windows, called browsers, provide a consistent approach for interacting with the Pascal source code or the execution state of the program. Incremental compilation allows the programmer to specify debugging actions in Pascal, eliminating the need for a separate debugging language.

Incremental compilation in Magpie

Magpie is an interactive, integrate programming environment that supports the development of Pascal programs a powerful, single-user workstation. Incremental compilation techniques are used to provide quick feedback on static errors and to ensure that a program is always ready for execution even while it is being edited. Magpie performs syntax and static semantic analysis with the unit of incrementality of a single character. Magpie uses incremental compilation to achieve performance levels that allow Pascal to be used interactively and as its own debugging language.

Linear queries in statistical databases

A database is compromised if a user can determine the data elements associated with keys which he did not know previously. If it is possible, compromise can be achieved by posing a finite set of queries over sets of data elements and employing initial information to solve the resulting system of equations. Assuming the allowable queries are linear, that is, weighted sums of data elements, we show how compromise can be achieved and we characterize the maximal initial information permitted of a user in a secure system. When compromise is possible, the initial information and the number of queries required to achieve it is surprisingly small.

The design of a language-directed editor for block-structured languages

A language-directed editor combines the text manipulation functions of a general-purpose editor with the syntax-checking functions of a compiler. It allows a user to create and modify a program in terms of its syntactic structure. The design of a user interface and an implementation for one such editor is described in language-independent terms. The design rationale is given. The implementation is outlined in terms of its major data structures.

Contexts: a partitioning concept for hypertext

A hypertext system makes a good information management system for a software development environment. However, existing hypertext systems provide poor support for collaboration among members of development teams. We examine several models for forming partitions in a hypertext data base and define our notion of contexts, a partitioning scheme that supports multi-person cooperative efforts.

Collaborative writing with hypertext

The authors introduce the concept of hypertext and focus on how hypertext can facilitate writing activities. A survey of the capabilities of existing hypertext systems and current research activities is included. >