This paper presents a guided tour system for the WWW. It is a module for the Webvise open hypermedia system that implements the ideas of trails and guided tours, originating from the hypertext field. Webvise appears as an open hypermedia helper application to the user and stores the guided tours in an XML format called OHIF separated from the WWW documents included in the tour. The main advantages of the system are: (1) a browser independent format in terms of HTML and PNG-based image maps for reading the guided tours; (2) support for a familiar metaphor, namely, a metro route map; (3) overview maps and route maps with indication of which stations of a tour have been visited; and finally (4) support for arbitrary web pages as stations on the tour. The paper discusses the Webvise Guided Tour System and illustrates its use in a digital library portal. The system is compared to other recent Web-based guided tour systems, and it is argued that Webvise Guided Tour System solves a number of prior system problems.

Abstract This paper presents a static approach to exception handling. The static approach is proposed as a consequence of an examination of existing language constructs for exception handling in which several trouble spots have been revealed. The static approach consists basically of one concept, namely the sequel concept. Although the sequel concept is sufficient to specify exception handling within a program, one additional concept is introduced, namely the derived definition concept that is introduced as a generalization of the derived type and generic concepts from Ada. The main advantages of the static approach are first that it is truly static as opposed to the existing language constructs in which dynamic association is used in some way or another; and, secondly, the language constructs for exception handling are simple, easy to implement and based on familiar concepts.