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It is difficult for users to navigate large document spaces, since they often
experience a disorientation problem.  A variety of
tools are being tested to assist users. These include navigational tools
such as browsers and lenses, passive processes such as history lists,
bookmarks and filters, and active processes such as agents. At the
University of Pittsburgh, Korfhage and Lewis are examining a variety of visual
interfaces for information retrieval. [10,9,14,15]
The CASCADE (Computer Augmented Support for Collaborative Authoring and
Document Editing) research testbed has been developed to explore the
integrated use of navigational tools, passive processes and active processes
(agents) to support collaborative authoring of documents
CASCADE employs a variety of active and passive processes that aid in the
identification of important documents. CASCADE has the traditional
mail filters, history
lists, and bookmarks. In addition, at startup time, CASCADE produces ad hoc pages
describing recent activity of users including links to relevant documents.
Users can prepare "reports" with varying levels of detail on
user-selected sets of documents.
These reports contain system-generated links to the relevant documents.
Finally, agents are under development that will identify patterns of
activity on documents that may be of interest to a given user. While these active
and passive processes are critical components of any integrated approach to
augmented navigation, this paper reviews only those efforts to integrate a
coordinated set of navigational tools to aid in the navigation and
management of complex document spaces. Our work has used the standardization process
as one which typifies medium-sized document spaces in which collaborative
work takes place. Usage suggests that the system is also
applicable to sets of legislative documents, legal cases, instructional materials,
software projects, to name a few. Further, we believe the
navigational mechanisms described here are applicable to any situation
where complex objects with relations must be organized and navigated. Thus,
for example, we believe the work is equally applicable to browsers for Web
The current research builds on a large number of efforts,
including seminal work on browsers [2,4], lens
[12,11,18,1], texturemaps [16,8,15],
and stucturemaps. Our work
looks to integrate systems of these types to provide appropriate navigational aids
for the users at appropriate times. Theoretically, the work builds on Spring
and Jennings  using the rules for mapping abstract data to
virtual spaces. The research project is designed to explore the
capabilities of the tools individually and more importantly in combinations
that assist a user in navigation.
Each of the tools may be thought of as a map of a given scale and with a
given level of detail that can be used together to aid movement through
complex, abstract document space. The research makes several assumptions, including:
- A bitmap display of 1000 x 1000 pixels with a 24 bit depth and a
refresh rate of 30 cycles per second may be viewed as having a bandwidth
of 1,000,000 pixels * 3 bytes * 30images/second or 90MB/sec.
- Careful usage of preattentive stimuli allow users to process
large amounts of data in parallel. Hue is an ideal preattentive stimulus
for testing, but other less dominant preattentive stimuli may also
- Navigation tasks involve at least four kinds of processes --
finding groups of objects of interest, finding specific objects of
interest, following interesting paths, and tentative
exploration of objects of given attributes.
- Documents and document components are objects with attributes and
The tools being implemented in CASCADE attempt to capitalize on these
assumptions. We view a document space as a semi-structured space populated
with objects that have multiple attributes and multiple relationships.
Four related tools are implemented that focus on the different kinds of
navigation tasks. These include:
- Docuverse. The Docuverse tool depicts large numbers of
objects. It provides an overview of the document space with the intent of
helping the user to identify areas of the document space, i.e. collections
of objects, that may be of interest based on recognition of specific colors,
color textures, collection size, or changes in collection size.
Docuverse shows minimal structure. In the prototype, this structure is
the file system. The next generation will show basic document structure,
but will not show full document structure as might be apparent via links. At
the current time, objects represented in Docuverse show only one
attribute of the selected object at a time. Thus, a given display might
show the size, age, usage, number of links, or type of a document. An area of interest is
selectable and selection will yield, based on the mouse button used, another
iteration of a Docuverse plot with the selected area as the new center of
focus, or generation of a Webview rooted on the selected area.
- Webview. The Webview tool is a traditional tree browser.
The current directory (or document container) is shown with its components
and containers. The containers are recursively expanded showing their
contents. Individual documents and links between documents are viewed on a
large pannable canvas. While the prototype currently displays only
hierarchical links, future versions will display other types of links as
well. Thus, instead of reflecting the hierarchical structure of a document,
the Webview might show document link distances, without regard to document
structure. Selecting a container object in the tree causes the root of the tree
to change -- to the new container. While the number of levels shown at any
time is arbitrary, we have chosen to show only three levels at the current
time to maximize performance. In addition, very large directories below the
first level are simply indicated and not expanded for the same reason. The
user navigates up the tree by clicking on the root node of the tree.
Clicking on any subnode does one of two things: 1. 1f the subnode is a
directory(container) the tree is rerooted at that container; 2. if the node is
a content node, it is displayed in the view window. When a document object
is displayed, Landmark tools become accessible.
- Landmarks. Individual documents or components may be
arbitrarily large, necessitating intradocument navigational aids. While
text search has traditionally been used for intradocument navigation, a
variety of additional information is becoming available with the
increasing use of explicitly structured documents. Landmarks within a
document may be chosen to reflect the semantic, structural or other
attributes of the document. In the current implementation, two landmark
maps may be appended to a
document in CASCADE. Mural shows the location of all links in a document.
Tilebar shows the frequency of occurrence of up to three sets of terms across a document.
Each provides a view across the
entire document. A variable sized thumb in the scroll bar
identifies the portion of the document
displayed in the view window. Navigation to any place in the document of
interest is accomplished by aligning the thumb with the area of interest on
the Landmark map.
- Preview. Metadata about a document can be used to provide a lens
for the user about the desirability of opening a given document or
traversing a given link. Most lenses attempt to assist the user by
providing information about a given document in advance of a commitment by
the user to traverse a link or open a document. In CASCADE, there are two
kinds of previews. First, all anchors are color-coded to define the type
of the destination node, as they are in the Webview. Thus, visually, the
user knows the type of node that is at the end of the link simply by
glancing at the color. The anchor also carries the name of the destination
node, and for system-generated links, this identifies the author and the
creation date. The second level of preview is accomplished by clicking on
the anchor which brings up a small window which provides information about
all the attributes of system-generated nodes -- for the purpose of the
standards CASCADE research, these kinds of nodes were generated when users
commented on a document.
The next four sections describe these navigation tools in somewhat more detail.
Up: Multi-level Navigation of a
Previous: Multi-level Navigation of a
Sun Sep 22 09:13:45 EDT 1996