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.

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.

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 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. Schlörer's 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.

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.