13.1 The Gloor/Dynes Hypertext Engine

The Gloor/Dynes hypertext engine [Glo93a] has been developed as a hypertext shell on the Macintosh in HyperCard extended by XCMDs' in C [Win90]. It has been used for various hypertext projects, among others for the "Animated Algorithms" project and the DAGS multimedia proceedings series described later in the book. It embodies most of the popular concepts found in Web browsers on a standalone platform, but also offers some unique features not commonly found in hypertext systems. This section focuses on the main characteristic of the Gloor/Dynes hypertext engine which is its support for hierarchical document structures.

Figure I.70 Sample hypertext page of the Gloor/Dynes hypertext engine

One of the core concepts that distinguishes our system from other hyperdocuments is the ability to examine ideas and concepts at different levels of abstraction, ranging from a "broad and shallow" level to a "narrow but deep" level. This feature allows the user to read the material first at an abstract level and to get an understanding of what the essential points of a certain section are. The capability to quickly pop up to a high level of abstraction also lessens the chance that the reader loses the forest for the trees. For use as a reference, being able to browse the text at various levels of abstraction enables the user to quickly filter relevant sections from those less important.

Figure I.71 Hierarchical document hypertext structure

To realize this concept the hyperdocument is composed of nodes with four different detail levels (fig. I.71). The first detail level gives a broad overview of each of the seven parts of the book and is composed of nodes incorporating the text making up the preamble to each part. Nodes of the second level consist of the introduction to each chapter, detailing what each chapter is about. Third level nodes contain the preambles to each of the chapter sections. The fourth level nodes consist of the actual text which makes up each chapter section, encompassing most of the text of the book.

We are offering multiple, partly redundant means of getting from one node to another. We are distinguishing between intrinsic and extrinsic means for navigation. Intrinsic means consist of hardwired links between nodes, generated automatically by the text-to-hypertext conversion. On the other hand, we are also offering extrinsic means of browsing: key word search, book-like lists, the navigation diamond, and the viewfinder discussed in the next chapter.

Nodes may also include references to graphics or to text contained in other nodes. Animations and figures are accessed in their own window. Also referenced are (1) display equations, (2) theorems, and (3) pseudocode for describing algorithms. Each of these is available as a pop-up window where referenced.

Each hyperdocument consists of two part. The hypertext contains the full hyperdocument as one large HyperCard stack. A small file, the personal file, is a template for individual users to copy onto local storage (hard disk or floppy). The personal file stores individual modifications and other personalizations the user makes to the hypertext stack, which, eventually being on a CD-ROM, may not be modifiable.

Some of the personalizations include methods for recording thoughts and making notes. The interface contains provisions for annotating individual nodes, and annotating links between nodes. Annotations remain attached to the annotated object, and there are options for automatically viewing link annotations when the link is invoked. The node annotation is signaled through the use of an icon on the navigation panels of the hyperdocument (fig I.72).

Figure I.72 Hypertext user interface with navigation panels

A book mark facility and a user log are also available. The book mark facility allows the user to write a brief note explaining the importance of the node. The user log is a free-form floating text window that can be called at any point and be used for any purpose. More ambitious users can also add new links. User inputs are saved to the personal file when the browsing session is concluded, and can be reloaded upon commencement of the next browsing session.