available for the Macintosh include Director 
from MacroMind (San Francisco, CA) and 
Authorware Professional from Authorware, 
Inc. (Minneapolis, Minn.). Guide from Owl 
International is an example of an authoring 
tool for both IBM and Macintosh computers. 
KMS is an authoring tool available for UNIX 
based workstations. There are few research 
prototype engines for unix stations, and even 
fewer commercial engines. 
The choice for an appropriate authoring tool 
for a certain application will depend on the 
needs of the individual building the system 
and the specific features required for the 
application. The following paragraphs 
outline a tentative set of features for choosing 
an authoring tool for building a 
photointerpretation information base into a 
hypermedia system. 
The authoring tool should have hypermedia 
functions which will help to dynamically link 
text, images, graphics, video, sound or 
animation to additional information. These 
functions are not explicit in all authoring tools 
today. In Hypercard, for example, when the 
designer opens a new card or stack, finds 
himself with a blank card in which he needs 
to build each and every element of the 
system. All the links, except of the most 
trivial, need to be programmed in Hypertalk. 
The authoring tool should also include an 
explicit representation of the network 
structure in its user interface. In most current 
systems that network is only present inside 
the computer and it is up to the user's 
imagination to picture how the entire network 
is structured. A dynamic overview showing 
the structure of this network is desirable 
(Nielsen, 1990). Hypercard does not 
embody a browser to permanently show 
overview diagrams of the network structure, 
while some of the unix based systems, like 
KMS, do. Such systems, though, are not as 
widely available and as inexpensive as 
Hypercard. 
The authoring tool should contain the basic 
tools needed by any author, such as 
integrated word processors, spelling checker, 
and graphics editors for preparing the text 
fields or making good illustrations. Text 
files, graphics, and animation should also be 
easy to import from other applications. 
Multiple graphics formats should be 
recognized and supported. The multimedia 
system should also take advantage of the 
particular graphics hardware and it should be 
able to handle all the colors and resolutions of 
the hardware. It should also supply drivers 
for controlling external media such as laser 
disk players and other remote media 
peripherals. 
An authoring system should also provide for 
integrating the output of external applications 
into the system and to actively and 
dynamically interact with an expert system 
environment. NexpertObject, an expert 
system tool available from Neuron Data, 
377 
provides an integration module for 
Hypercard. HyperX (from Millennium 
Software) is an expert system tool written in 
HyperTalk that integrates with Hypercard as 
well. 
While one of the newest interactive 
multimedia tools is digitized sound, it does 
not appear that a hypermedia interpretation 
system will be greatly profited from digitized 
sound, especially if one takes in account the 
storage requirements. It should be mentioned 
though that all Macintosh II machines include 
a built-in sound chip that can play back 
digitized sound and there are external sound 
digitizers available from third parties. There 
are also boards and drivers for the MS- 
DOS/Windows machines as well. Single- 
screen interactive video, which implies 
showing motion video and computer 
information on the same screen is possible by 
obtaining a single-screen board from third 
party manufacturers. 
A special hardware concern in the design of 
hypermedia is the storage space needed for 
the multimedia in hypermedia, especially if 
digitized images, voice, and video are used. 
Some writable optical disks exist and can be 
used to store between 550 and 650 
megabytes of data. A variety of 
compression methods and formats are also 
being developed that could help alleviate the 
problem. Another hardware requirement is 
for larger screens (19-21 inches). Larger 
screens will allow students to see more 
hypermedia material at the same time and 
allow room for various extra user interface 
features such as permanently shown 
overview diagrams. 
An authoring system used for 
photointerpretation training should maintain 
records of students who participate in the 
course. The records might include such 
things as the number of correct answers a 
person made, or how long it took a particular 
person to finish a specific section. 
It should be easy to learn and use without the 
support of a full-time programmer or a 
hardware engineer. It should not require of 
an expert photointerpreter to learn and use a 
programming language to create a 
hypermedia application. However, it should 
either contain its own procedural language or 
offer a direct access to such a language for 
those who wish to program advanced or 
additional features. It should also offer 
context-sensitive help for both the developers 
and its users. 
AUTHORING HYPERMEDIA SYSTEMS 
Building a hypermedia system is often called 
authoring a hypermedia system. Authoring 
in hypermedia is different from regular text 
authoring in the sense that the author must 
provide opportunities and priorities for 
knowledge exploration instead of ordering 
users to read sequentially (Nielsen, 1990). 
This is accomplished by first establishing an