%====================
\section{Error Codes}
%====================
\label{app:errors}

\hrule
\vspace{1em}

This appendix gives a list of all of the errors that were made in the
dialogues.  We have divided the errors into two groups, those that we
have attributed to the system, and those that we have attributed to
the user.  System errors include giving the wrong information (or
wrong interpretation) of the domain rules, and computing the wrong
amount of time it takes to complete the various tasks.  Even if the
error resulted from a user suggestion or comment, it is still
attributed to the system, since she is responsible for correcting such
mistakes.  User errors, on the other hand, include problems with
interpreting the task that was given; for instance, if part of the
task is forgetten, or if the task is incorrectly understood.  Even in
cases where the system made the incorrect interpretation, or suggested
a plan that didn't meet the user's task, the error is still attributed
to the user.

%-------------------------
\subsection{System Errors}
%-------------------------

The system errors that were observed in the dialogues have been listed
below.  These errors have been categorized into three groups.  The
first involves resource conflicts.  The second involves violations of
the properties of objects.  The third involves mistakes in computing
the duration of actions.  These errors are prefixed by {\bf R}, {\bf P}
and {\bf T}, respectively.

\begin{description}
\item [R1:] {\em Resource conflict.} Some piece of rolling stock
(i.e., an engine, boxcar, or tanker) was scheduled to be
used for two different tasks at the same time.

\item [R2:] {\em Train Crash.} Two trains are scheduled on the same
piece of track running towards each other.  Since the lines are single
tracks, they will collide.

\item [P1:] {\em Orange juice can not be transported in boxcars.}  Both 
the system and user instructions mention that tanker cars are to be
used for shipping orange juice.

\item [P2:] {\em Tankers can not move by themselves.}  The system must
have thought that a tanker car was not a piece of rolling stock, but
was a tanker truck.

\item [P3:] {\em Orange juice is not available at the orange juice
factory.}  Orange juice must be made.  The user must bring a boxcar of
oranges to the factory to make a tanker's worth of orange juice.

\item [P4:] {\em It is not the case that an engine can pull at most 
three boxcars or tankers.}  This should only be a restriction on
full boxcars or tankers.  The system map says ``Any engine can pull at
most three loaded boxcars or tankers cars, and any number of unloaded
cars.''

\item [P5:] {\em An action is missing.}  The plan is missing some action 
that is necessary.

\item [T1:] {\em It takes one hours to unload oranges, make OJ, 
and load the OJ into tankers, not three.} The system instructions are
not clear enough about this.  The system map reads ``One boxcar
oranges converts into one tanker load.  Any amount can be made in one
hour.''  The intended interpretation of ``Any amount can be made in
one hour'' is that it includes loading and unloading.

\item [T2:] {\em It takes an hour to load or unload any amount of cargo
on a train, not an hour for each boxcar or tanker.}  The system
instructions specify this clearly.

\item [T3:] System confused the time it takes to get from one city an
adjacent one.

\item [T4:] System forget to include the time it takes to complete
some task.

\item [T5:] Some error occurred in computing the amount of time
required.  However, from the dialogues, it is not possible to pinpoint
the exact error that was made.

\end{description}

One extra ``error'' that we noted involved scheduling trains going in
the same direction on a rail line connecting two cities.  The system
instructions are not clear whether this is to be allowed.  ``The rail
lines are single tracks, so two trains cannot simultaneously occupy
the same section of track.''  Due to the frequency of occurence, we
did not mark cases where the system scheduled the trains one hour
apart.  But we did mark occurences of the following, but did not view
them as makeing the proposed plan invalid.
%
\begin{description}
\item [R3:] {\em Two engines can not travel together or immediately
following each other.}  There should be at least an hour delay between
trains goig in the same direction on the same track.
\end{description}


%-----------------------
\subsection{User Errors}
%-----------------------

The errors that the user made are given below.  Some of the more
common errors have been classified, while all others are grouped into
{\bf U}.

\begin{description}
\item [U1:] User misunderstands what is meant by a ``round trip''.
\item [U2:] When asked to deliver a boxcar of some good, the user
unloads the boxcar at the destination instead of leaving it loaded.
We did not count such misinterpretations as making the plan invalid.
\item [U3:] The task called for the boxcar to be unloaded, which the
user forget to do.  We did not count such problems as making the plan
invalid, as long as there was enough time left over to do this.
\item [U4:] User mixed up a time constraint, or forgot one.
\item [U5:] User misunderstood the task, or didn't finish it, or
ignored part of it.
\end{description}









