In the WebBook and Web Forager interface , web
pages are collected into books, where books can be organized on the
desk or on the shelves. Pages and books can also be left hanging in
the air. Bookmarks attached to the lower edge of the book which
provides direct access to certain pages in the book. Thus, the lowest
level nodes of the presentation hierarchy are the page and bookmark
nodes, under the book node at the second level. At the third level are
the desk, the shelf and the air nodes (Figure ).
While links can also be considered as a node, for the simplicity of
the discussion they are omitted. Let's examine each node and link, and
their presentation hierarchy model attributes and functions along with
factors influencing them.
- Page node: Page is a singular node, thus its capacity is
1. Its space requirement can be changed dynamically as the user
resizes the page. The representation function simply draws the
contents of the web page (I).
- Bookmark node: The capacity of a bookmark node is 1. Its
space requirement depends on the length of the bookmark label. The
representation function simply draws the label on the lower edge of
- Book node: Theoretically, there is no limit on the
number of pages a book contains, however its capacity is limited by
the human capabilities to search for pages linearly. Books typically
use a page-sized screen space when they are closed, and twice that
amount when they are open. Pages in a book (I) are organized in a
linear order where the layout function may simulate the shuffling of
pages in a rapid manner. The representation function of the book
draws a colored cover with the title printed on the front cover.
- Desk node: The capacity of the desk node is limited by its
size which is fixed. The layout function is responsible for organizing
ages and books (I) arbitrarily overlapping on the two-dimensional desk
space. Its representation function draws a three-dimensional view of
the desk on the screen.
- Shelf node: The capacity of the shelf node is limited by the
number of rows and the quantity of books it can hold in each row. Its
space requirement is also fixed. Books can be organized into shelves
at different levels and in a linearly ordered fashion on each shelf.
Its representation function draws a three-dimensional view of the
- Air node: The capacity of the air node is
limited by the visibility pages and books due to occlusion, and by the
human capabilities to recall the locations of them. Its space
requirement is also fixed, filling up the rest of the screen
space. Pages and books (I) can be organized arbitrarily in
three-dimensional space of the air node with appropriate scaling. Its
layout function also allows the user to bring a page or book in the
- Bookmark-Page link: This link indicates that a bookmark can
be used to access a page. Typically, clicking on the bookmark brings
the associated page into view. Its footprint depends on the textual
label of the bookmark.
- Bookmark-Book link: Bookmarks of a book have very low
access costs because they are always visible, thus they also have high
- Page-Book link: Users typically access pages in a book
by turning pages one by one or shuffling them in a rapid manner.
Since pages are organized linearly in the book, access costs grow as
the number of pages in the book increase. Users can also access pages
from the bookmarks attached to the lower edge the book, giving them
direct access to certain pages. Bookmarks typically improve access
performance. The footprint of a page in a closed book is rather low
since only the book title and the cover color contain information that
might lead to the pages sought. An open book has a higher footprint
since page contents are shown. However, only two of the pages are
shown at the same time.
- Page-Desk link: In order to access pages from the desk users
need to drag it from the desk and leave it in the air. The footprint
of a page is quite high, as it is basically a small size image of the
- Page-Air link: Similarly, users drag a page in the
air in order to access it, thus the access cost is not much. The
footprint of a page in the air is also quite high due its visibility.
- Book-Desk link: Access cost and the footprint attributes are
similar to that of the page-desk link.
- Book-Shelf link: In order to access a book from the shelves,
users similarly drag the book from the shelf. The foot-print of a page
is visible as books are organized in such as way that their covers
face the user. However, reading the book titles may be hard.
- Book-Air link: Access cost and the footprint attributes are
similar to that of the page-air link.
Sun Sep 13 18:34:46 EDT 1998