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\begin{center}
\smash{\parbox[b]{\textwidth}{\small Notes prepared for ARPI Ontology
Kickoff Meeting, held October 12, 1994.  $\copyright$ Copyright 1994
by Jon Doyle.\\[.5in]}}{\huge\bf Critique of KRSL 2.0.2}\\[1pc]
{\large\bf Jon Doyle}\\
MIT Lab for Computer Science\\
{\tt doyle@lcs.mit.edu}\\
October 11, 1994
\end{center}

\begin{abstract}
  The current KRSL plan specification language treats information
  traditionally contained in plans reasonably well, but does not
  provide good means for representing economic information about how
  agents consume, produce, and choose among resources, and provides
  essentially no means for representing information about the
  rationales (reasons, decisions, and explanations) underlying
  plans.  In consequence, planning agents cannot use KRSL to
  cooperatively make decisions and evaluate and repair plans, as
  they cannot use KRSL to communicate useful information about their
  needs (in order to evaluate plans) and reasons (in order to modify
  plans).
\end{abstract}

The KRSL plan-representation language is intended to provide a common
language to ARPI groups for specifying information about plans and
communicating such information among modules.  The clear benefit of
such a common language is that it simplifies the task of integrating
modules by getting them all to speak the same language, rather than
having to design a large numbers of point-to-point translators of
idiosyncratic representations.  Unfortunately, the current version
KRSL facilitates communication of only a portion of the information
needed by mixed-initiative planning systems.  It focuses on
describing the overt structures of objects and actions in a way
completely appropriate to traditional AI planning systems.  But it
provides flawed means for specifying economic properties of agents and
resources, and provides no standard means for communicating plan
rationales.

In the original ARPI vision of human-computer cooperative planning,
human planners would work with automated systems to present commanders
with a short list of primary, qualitatively different options, the
idea being to give the commanders a good idea of the range of
possibilities seen as reasonable by the planners.  To allow the
commander(s) to choose wisely, these options must be accompanied by at
least a sketch of their underlying rationales if the options are not
absolutely transparent (as is rarely the case).  These rationales
indicate the primary planning assumptions and decisions making the
options plausible; the underlying assumptions about conditions and
responses, the underlying assumptions about the relative importance of
different strategic and tactical aims and principles, and the
principal choices among equally good alternatives (equivalently, the
dimensions of simple variability).  One plan might presume that some
position will hold without fail, or might chance greater risks than
another, or might sacrifice one goal to accomplish another.
Commanders need to know these things about the options to decide among
them.  For similar reasons, replanning systems designed to repair or
revise large-scale plans in light of changed information also need the
rationales of plans if they are to do anything other than replanning
from scratch.

The current KRSL specification provides no standard means for
communicating useful plan rationales.  One can state that a plan
achieves a specific goal in KRSL; but one cannot say much about
underlying assumptions about conditions, or the alternatives
considered in selecting this plan over others that achieve the goal,
or about the preferences that lead to this selection, or about the
importance of this goal to others.  Accordingly, KRSL should be
improved to permit convenient specification of plan rationales and the
information contained in them.  Past work on reason maintenance
\cite{Doyle79a,Doyle-Wellman90} and reasoned deliberation
\cite{Doyle80} provides suggestions for some elements of rationales,
namely argument fragments and descriptions of decisions.

Improving KRSL's language of plan rationales in these ways will
directly benefit the designers of intermediate-level planning system
components (as in the ACP task), who will use this portion of KRSL to
communicate rationale information crucial in revising plans.  Plan
rationales indicate which parts of a plan are separate from each
other, or more generally, the dependence of parts on others, and thus
provide the basic information needed to minimize the portion of a plan
needing repair.  But rationales also include the preferential
judgments or decisions used in choosing one alternative part over
others, and thus provide both immediate alternatives to consider in
revisions, as well as providing strategic information about what
revisions are more important than others.  The current KRSL, in
focusing on communicating only plans but not rationales, provides only
plans which modules may take or leave as wholes, with no indication of
component interdependence or importance.

One key element of plan rationales present in KRSL but treated
inadequately is preferential and utility information.  The language
includes a construct for specifying preferences among things, but
without any clear meaning given to the things so related.  The
descriptive text seems to indicate that preferences relate
propositions (sets of possible worlds) or descriptions of such, and
mean that every world satisfying one proposition or description is
preferred (perhaps weakly) to every world satisfying the other.  This
semantics is pretty useless in practice, for it forbids distinguishing
tradeoffs preferentially---that is, all outcomes trading off mutually
unsatisfiable conditions must be indifferent.  The language includes
means for stating utility functions, but provides no structure for
stating the standard constructs of multiattribute utility theory
\cite{Keeney-Raiffa}.  Accordingly, KRSL should be corrected to
provide a library of standard constructs from multiattribute utility
theory making convenient specification and composition of subutility
functions \cite{Wellman-Doyle92}, and to draw on recent work on
stating propositional preferences correctly
\cite{Boutilier93,DSW91,Doyle-Wellman94,Mantha94,Tan-Pearl94,Wellman91d}.  It
should also incorporate standard constructs relating planning goals to
preference and utility measures, including both the theoretical
constructs just mentioned, and libraries like those of Haddawy and
Hanks \cite{Haddawy-Hanks90,Haddawy-Hanks92} identifying specific
utility functions approximating common types of planning and
problem-solving goals.

Preferences constitute only one form of economic information treated
inadequately by KRSL.  The current language provides rudimentary means
for specifying production and consumption of resources, but little is
expressible beyond the simple fact of production or consumption.
Standard economic theory provides additional concepts for
systematizing specifications of economic behaviors through its general
and special notions of production functions, which indicate how
consumption depends on production and vice versa.  In addition,
standard economic theory provides a taxonomy of different types of
consumers, producers, resources, and auction methods useful in
describing market and choice mechanism, as well as descriptors of the
structure of production functions, such as ``complementarities''
(necessary coordinations among resources, e.g., guns aren't much use
without bullets and vice versa).

Put together, these improvements to KRSL's economic language should
prove very useful to communicating plans and their rationales.
Planning experts working to codify planning problems will find the
improved and expanded language significantly more useful in accurately
characterizing planning situations, resources, and tasks, as the
language will finally be able to express in convenient and standard
ways both the ordinary production/consumption relationships among
actors and resources and the strategic importance among different
resources and activities within a plan.  For example, the current KRSL
provides only indirect ways of saying that tanks need ammunition and
vice versa, or that transporting more fighter pilots is more important
than transporting more press officers.  The improved language should
make accurate expression of such information possible, and will
facilitate the sharing and communication of this information among a
wide range of systems, both human and machine.

Some other problems include the following.
\begin{itemize}

\item There is no way to refer to the context in which statements are
  valid except temporal contexts.

\item Resource usage records just seem to indicate current usages.
  Can they also indicate schedules of usages under different conditions?

\item Can quantities be schedules?  (Mappings?)  Mappings from
  contexts to quantities?

\item There are no assumptions (nonmonotonic) apart from defaults in
  objects.  Do concepts have no default values?

\item There are no handles on representations themselves.

\end{itemize}

\newpage
%\bibliography{abbrevs,bib,general,crossref}
%\bibliographystyle{abbrv}

\newcommand{\noopsort}[1]{}
\begin{thebibliography}{10}

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C.~Boutilier.
\newblock A modal characterization of defeasible deontic conditionals and
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\newblock In {\em AAAI Spring Symposium on Reasoning about Mental States},
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\bibitem{Doyle79a}
J.~Doyle.
\newblock A truth maintenance system.
\newblock {\em Artificial Intelligence}, 12(2):231--272, 1979.

\bibitem{Doyle80}
J.~Doyle.
\newblock A model for deliberation, action, and introspection.
\newblock AI-TR 581, Massachusetts Institute of Technology, Artificial
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\bibitem{DSW91}
J.~Doyle, Y.~Shoham, and M.~P. Wellman.
\newblock A logic of relative desire (preliminary report).
\newblock In Z.~W. Ras and M.~Zemankova, editors, {\em Methodologies for
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\bibitem{Doyle-Wellman90}
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\newblock Rational distributed reason maintenance for planning and replanning
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\newblock In K.~Sycara, editor, {\em Proceedings of the DARPA Workshop on
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\bibitem{Doyle-Wellman94}
J.~Doyle and M.~P. Wellman.
\newblock Representing preferences as {\em ceteris paribus} comparatives.
\newblock In S.~Hanks, S.~Russell, and M.~P. Wellman, editors, {\em Proceedings
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\bibitem{Haddawy-Hanks90}
P.~Haddawy and S.~Hanks.
\newblock Issues in decision-theoretic planning: Symbolic goals and numeric
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\newblock In {\em Proceedings of the DARPA Workshop on Innovative Approaches to
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\bibitem{Haddawy-Hanks92}
P.~Haddawy and S.~Hanks.
\newblock Representations for decision-theoretic planning: Utility functions
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\newblock In B.~Nebel, C.~Rich, and W.~Swartout, editors, {\em Proceedings of
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\bibitem{Keeney-Raiffa}
R.~L. Keeney and H.~Raiffa.
\newblock {\em Decisions with Multiple Objectives: Preferences and Value
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\newblock John Wiley and Sons, New York, 1976.

\bibitem{Mantha94}
S.~Mantha.
\newblock Towards a logical foundation for qualitative decision theory.
\newblock In S.~Hanks, S.~Russell, and M.~P. Wellman, editors, {\em Working
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\bibitem{Tan-Pearl94}
S.-W. Tan and J.~Pearl.
\newblock Specification and evaluation of preferences for planning under
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\newblock In J.~Doyle, E.~Sandewall, and P.~Torasso, editors, {\em Principles
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\bibitem{Wellman91d}
M.~P. Wellman and J.~Doyle.
\newblock Preferential semantics for goals.
\newblock In {\em Proceedings of the National Conference on Artificial
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\bibitem{Wellman-Doyle92}
M.~P. Wellman and J.~Doyle.
\newblock Modular utility representation for decision-theoretic planning.
\newblock In {\em Proceedings of the First International Conference on AI
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\end{thebibliography}

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