Many research projects have used some kind of lens or link preview to provide additional information about a link before it is traversed[12,11]. The Vibe system provided a lens with user-selectable contents. Preview represents the relationship between the current document and a linked document by showing metadata about the linked document through the anchors that exist within the document or by some additional information made available when the cursor enters the anchor area. Within CASCADE, there are two types of Preview. At all times, anchors show information about the type of the destination node, if it is known to CASCADE. For links created and maintained by CASCADE, the name of the node reflects the author and date of creation of the node. The user may also create a manual link in CASCADE in which case, naming is at the discretion of the user. The system makes some effort to determine the type of the destination node -- whether it is in the CASCADE space or somewhere else in the WWW, whether it is a file type requiring special processing -- e.g. postscript or image files, etc. The kind of information this makes available is shown in Figure 6 where the colored buttons indicate the type of nodes that are the destination of the hypertext links. From this view the reader can know who the author of the comment is (label information) as well as the type of the destination node (color coding as in the Webview and Docuverse).
Figure 6: Link Preview
Some consideration has been given to overloading this view with yet additional information. For example, one might use variable size levels on the buttons to show age, number of traversals, size, etc. As CASCADE moves to DBMS control of anchor and link information in accord with the storage layer architecture laid out in the Dexter Hypertext Reference Model, we will probably revisit this possibility.
Preview also employs a popup window which displays several pieces of information such as type, status, disposition, date of the creation, author, location, abstract and so on (Figure 7). In CASCADE, the popup Preview is more than a passive display of attributes. This popup Preview allows the user to change the attributes of a comments and annotate the reason for the change. The window also shows the history of attribute changes. Multiple popup lenses can be viewed simultaneously but their size places limits on how many can be used simultaneously. Additional previews have been developed for instructional use of CASCADE. In some of these cases, the view is simply a report in which case much less screen territory is required and much more metadata information can be provided
Figure 7: Link Preview Popup