Acquiring, elucidating and conceptualizing 
such knowledge is the central task in building 
intelligent systems. Intelligent 
conceptualization is intellectually hard work, 
and it best comes about through an 
incremental and iterative process. 
While this paper argues in support of 
hypermedia, it is written in a linear, 
sequential manner. It will be an erroneous 
hypothesis to assume that the process of 
decomposing knowledge takes place in a 
series of successive steps. We, somehow, 
are doing many steps in parallel, while their 
implementation is normally taken place in a 
serial manner. Hence, the actual process of 
knowledge conceptualization is extremely 
hard. . 
IMPLEMENTING A HYPERMEDIA 
SYSTEM 
Once we have partitioned the specific 
photointerpretation knowledge into a set of 
nodes and links the next step is the 
implementation of the information base in a 
hypermedia system. À certain hypermedia 
environment is selected and the sets of nodes 
and links are formally represented and 
programmed. Assuming that a Hypercard- 
like system is selected, one needs to 
determine the nature of the stack(s) to be 
designed. The previously designed partition 
of the knowledge into selected nodes and 
links together with the need for easy and 
efficient navigation can help determine each 
stacks's structure. Hypercard supports 
single-frame, linear, tree, network, and 
combination stack structures (HyperCard 
Stack Design Guidelines, 1989). Given the 
complexity of the photointerpretation 
process, it is speculated that a network or 
combination stack structure might be most 
appropriate. A network stack structure is one 
in which students can explore in many 
different ways (e.g., visiting other cards or 
stacks). Navigation in network stacks may 
be by reference points (or hubs), stack maps 
or menus. 
Depending on the specific subject matter one 
may choose to include various levels of 
image interpretation tasks for the most 
significant aspects of general 
photointerpretation in one stack. Additional 
stacks may be required for advanced 
interpretation tasks and for specialized tasks, 
such as interpretation of specific geologic 
formations or specific tree species. 
Hypermedia systems permit and encourage 
one to build a system incrementally, creating 
new nodes/concepts and links as desired, one 
at a time. Indeed, building a hypermedia 
system is a cyclic, repetitive process. It is 
likely that the design of the stacks, cards, 
fields, buttons, etc will change significantly 
in the beginning. One approach that could 
help to cope with this iterative process is to 
think of several solutions, design all of them 
to a certain point, and then choose one for 
further development. 
379 
Some general guidelines for good stack 
design are outlined in the following 
(HyperCard Stack Design Guidelines, 1989). 
The system should exhibit a well organized, 
orderly, and well structured arrangement of 
cards, fields, graphics, and buttons so that 
students will be quickly able to learn, 
understand, and use the system structure, the 
most basic commands and the navigation 
options to locate needed information 
(Nielsen, 1990). The hypermedia cards can 
include as much text or graphical elements as 
appropriate, but screen-sized chunks of 
information should be mostly used because 
attaching more lengthy information to a 
hypermedia node that must be scrolled 
through on successive screens can be 
disorienting to the student. 
The hypermedia design should take 
advantage of the hypermedia functions of the 
selected authoring software system. It should 
put information in obvious and intuitive 
patterns so students can more easily locate, 
browse, and understand the 
photointerpretation knowledge. Good links 
should relate concepts (not words), provide 
minimum keystroke access to these concepts, 
and help students to see the relationships 
between concepts. 
Card and background layouts should be 
consistent for related cards. Navigation 
buttons should be on every card, grouped by 
function, and in the same place throughout 
the stack perhaps on the edges of the screen. 
The overall design should help the student to 
control the navigation. The students student 
should be able to find a certain piece of 
information quickly or soon discover that it is 
not in the information base within a minimum 
number of keystrokes. The stack's 
navigation must make use of menus, maps, 
textual reminders, you-are-here indicators, 
travel buttons, and progress indicators. The 
stack should also have a title card, a proper 
introduction describing the stack's purpose 
and organization including the stack's size 
and general layout, the stack's rules, and 
their options. Topical menus, tables of 
contents, and alphabetical listings should be 
explained. A button of "Help" or "How to 
use this stack" should be included on all 
cards. The system should also offer context- 
sensitive help. 
The photointerpretation hypermedia system 
should include a great number of aerial, 
oblique, and ground photos as well as a lot 
of illustrative diagrams such as cross 
sections, profiles, and block diagrams. The 
stimulus for seeking to include diagrams and 
photographs comes from the inherent 
complexity of the photointerpretation 
process. Incorporating photographic images 
will serve to illustrate conditions that are too 
complex for verbal explanation alone. The 
photographic images reduce the potential for 
confusion and misinterpretation by 
illustrating objects and conditions that might 
be misunderstood if only descriptive text 
were used. All potential uses of photos