Interactive computer graphics displays for hierarchical data structures. [Description of THESGRAF, in FORTRAN IV for CDC and IBM computers] Page: 4 of 10
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a term group composed of a primary descriptor (main term (MT)) and its
relations. In present form, our system displays hierarchical (broader
term (BT) and narrower term (NT)) and associative (related term (RT))
relations only, since these are the most appropriate to navigation
through the thesaurus space. Completeness suggests addition of the
other common thesaurus relations (SEE ALSO, USED FOR and USE) as well
as 'scope notes' and 'definitions', and these will most likely be
added in the future.
Figure 1 shows a typical thesaurus paragraph represented in the
traditional tabular form and in tree form on our color monitor. In
our representation, the main term appears at center screen and is con-
nected by vectors to its nearest hierarchical and associative rela-
tions (BT1, NT1, RT). Secondary neighbors (BT2, NT2) are linked to
the nearest neighbors, and, within the five levels depicted, parenting
and neighbor links are readily apparent.
Depth in the hierarchy increases from left to right, a concession
to the character representation of common computer terminals. (It
would have been more natural to increase depth downwards, and Indeed
we considered this first, but ultimately we rotated the display side-
ways in order to fit a convenient number of terms on the screen.
Color, case, and character size, keyed to relation type and dis-
tance, are utilized to facilitate visualization of term relationships.
The specific display enhancements used are not critical, and other
commonly available display enhancements (such as inverse video or half
intensity) would be just as appropriate. It is useful, though, to
provide some form of consistent visual cues to the user, so that his
segmentation of successive display frames into components does not
interfere with his perspective of the thesaurus.
In Figures 2 and 3, the effects of successive refinement of the
search are shown. In Figure 2, the user has selected one of the NT2
terms of Figure 1 as a candidate search term; the display shows him
the thesaurus neighborhood from this term's perspective and allows him
easily to assess whether this more specific term captures his intent
better than its broader neighbor. In Figure 3, a sibling of t.he Fig-
ure 2 term is expanded.
Movements of the focal point through a thesaurus neighborhood are
extremely simple for the user: he need merely designate the next term
to be displayed either by typing it into the terminal's keyboard, or,
with more advanced terminals, by aiming a light pen at the screen
position at which it is currently displayed. Focal point movements
are unrestricted to the user: he can move higher or lower in the
hierarchy or to any related term with equal ease, skipping intervening
levels as desired. He can move, in fact, to any point in the
thesaurus in a single step, although for movements beyond the current
screen bounds, he must obviously use the keyboard rather than the
light pen, and must know a specific term to which to transfer. Once
in the new neighborhood, he can once again make use of the light pen
for local movements. By contrast to the ease of movement provided in
the computer graphic display's direct associative link representation,
the user of a tabular alphabetic representation (whether computer
accessed or manual) must transform his internal concepts of his search
space to fit the alphabetic domain of the thesaurus. In most cases,
-3-
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Cahn, D.F. & Murano, C.V. Interactive computer graphics displays for hierarchical data structures. [Description of THESGRAF, in FORTRAN IV for CDC and IBM computers], article, May 1, 1980; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc1064427/m1/4/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.