Your Wish is My Command

1.3 Theoretical Foundations 11

FIGURE

1.1

Define

Drag

Drop

Defining a rule by demonstration.

If the engine is on a piece of straight track and there is straight track to its

right, then move the engine to the right.

Notice that programming is kept in domain terms, such as

engines

and

track,

rather than in computer terms, such as

arrays and vectors.

Also, in-

stead of dealing with objects indirectly through coordinates, users program

them by manipulating them directly; that is PBD (see Table 1.1).

Since a rule in Creator may not show all the steps involved, just their be-

ginning and ending states, it is not a representation ...