The step of forming one interactive document out of a collection of several interactive documents is an important issue. Usually a book is divided in several chapters, or a report consists of a couple of individual articles. Such a heterogeneous collection of documents can each reside in a different location (directory). Ideally this directory contains the whole environment (text, figures, programs and command scripts) for reproducing and defining interactions for the entire interactive document. Such an object-oriented philosophy (OOP), as described by Jon Claerbout in this report, requires that while including objects, such as articles or chapters, their interactivity is maintained. This requirement is not trivial, since an interactive document object usually consists of a directory or structured subdirectory tree.
We solved this problem in LATEX by creating a new 
include{path}{file}
command, which has two arguments. The first is the directory path name, indicating the location of the object-oriented document; the second is the name of the file that contains the actual text. This new command differs from the regular
one in that it automatically specifies the current working directory to be that of
the included document. In practice, this means when then reader views a heterogeneous
document, the current working directory associated with the interactivity
changes from chapter to chapter or from article to article.
The reader himself does not notice the change of environment, as he presses
buttons to start up some action.
It is not readily apparent what the best granularity of a heterogeneous document will be. As a starting point we have chosen an object-oriented document to be a self-contained article or book chapter. For other applications a different granularity may be more suitable.