Interactive Fiction and the Colossal Cave Adventure

Interactive Fiction

In recent years, a collection of stories has arisen referred to as
interactive fiction. At various places in the tale, the reader is
confronted with choices:

    Shall Elizabeth accept Darcy's invitation or not?

The story plot proceeds on different paths according to the reader's
wishes.

In such cases, the story DAG will contain nodes and dependencies to
cover all the variants. In place of the narrative thread, however, we
now have a narrative DAG, in which the points of bifurcation correspond
to the reader's choices. Possibly, the choices should be noted within
the narrative DAG. The narrative DAG may, of course, degenerate to a
tree if the alternatives do not eventually recombine to common sections.
Clearly, the author must not generalize the narrative DAG to contain
cycles, otherwise the reader, while reading only a single variant, may
see sections of the narrative repeated.


The World of Zork

At the extreme end of the interactive fiction scale is the class of
textual computer games such as The Colossal Cave Adventure, The Great
Underground Empire of Zork, and the like, which became popular in the
late 1970s. There is a parallel between the story of Phil in the film
Groundhog Day and that of the adventurer in these games.

In the latter, the adventurer, under the interactive control of the
player, explores a set of underground caves. In each cave, he/she has a
choice of passages for leaving it. These are not necessarily "good" or
"bad" -- they merely convey the adventurer to another cave, perhaps a
new one, perhaps one visited earlier. Simplifying for the moment, the
goal is to explore the underground world and build a map. On revisiting
an old cave, the player may make an alternative choice. He/she may also
restart the entire program, in effect "reliving" the day, learning from
the knowledge gained on previous visits.

We may think of the details of cave system as the semantic content of
the cave story; while each exploratory visit, or indeed the totality of
such visits, amounts to a threading created interactively. A "perfect
narrative" -- there may be more than one -- visits all the caves without
unnecessarily retracing steps[1].

    Footnote 1. A perfect narrative for one variant of The
    Colossal Cave Adventure can be found at

        http://rickadams.org/adventure/walk550.txt

    This is, of course, a spoiler for anyone who may wish to
    play the game.

Can the semantic content of the cave world be represented by the DAGs we
have proposed? There appear to be two alternatives. First of all, it is
clear that a map of the cave system takes the form of a graph, where the
nodes represent caves and the paths passages. A directed graph?
Apparently not, since most --though not necessarily all -- of the
passages can be traversed in either direction. It is an easy matter to
get around this by having the two-way passages represented by two
separate unidirectional ones. More seriously, however, the directed
graph is no longer acyclic.

What "stories" are told by the game? If a "narrative" is to tell only
of the steps taken by the adventurer exploring the caves (that is, a
transcript of the commands entered by the player and the responses
produced by the computer), then the map itself describes the semantic
content, and narrative threads must follow the directed paths.

If the "story" is to involve a description of the underground world
rather than a tour, however, the passages themselves become entities in
their own right, and must be represented by nodes. (Thus the description
will be able to note that a low small passage leads south from the Slab
room to the west end of the Twopit room.) Since the paths no longer
represent the passages, there may be no reason for the directed graph to
contain cycles[2]. Furthermore, the threading becomes once again a matter
for the story's creator.

    Footnote 2. But this writer has not yet convinced himself!

Let us revisit our earlier simplification. In actual fact, the Zorkian
world has other features: treasures which must be collected, puzzles
which must be solved, beings who help, or attempt to kill, the
adventurer, and so on. At one point in the Adventure world, one must
pick up a cage; later it will be used to catch a small bird; and in
time, when a huge green snake bars the way, the bird must be released to
frighten it off. Elsewhere there is a bottle, which can subsequently
be filled with oil, eventually to lubricate and free a door with rusty
hinges. Obviously, the DAGs or graphs which elaborate the cave nodes
contain many nodes of their own, with dependency paths across the cave
system.

We must conclude, then, while there are many similarities between the
structure of Groundhog story and the Zork narratives, the graphical
representation of the cave world calls for some generalization of our
DAG structures.