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Authored by Francisco Coelho
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... ... @@ -129,10 +129,10 @@ citecolor=blue,
129 129 \Acf{ASP} is a logic programming paradigm based on the \ac{SM} semantics of \acp{NP} that can be implemented using the latest advances in SAT solving technology. Unlike ProLog, \ac{ASP} is a truly declarative language that supports language constructs such as disjunction in the head of a clause, choice rules, and hard and weak constraints.
130 130  
131 131 \todo{references}
132   -The \ac{DS} is a key approach to extend logical representations with probabilistic reasoning. \Acp{PF} are the most basic \ac{DS} stochastic primitives and take the form of logical facts, $a$, labelled with probabilities, $p$, such as $\probfact{p}{a}$; Each \ac{PF} represents a boolean random variable that is true with probability $p$ and false with probability $\co{p} = 1 - p$. A (consistent) combination of the \acp{PF} defines a \acf{TC} $c = \set{\probfact{p}{a}, \ldots}$ such that
  132 +The \ac{DS} is a key approach to extend logical representations with probabilistic reasoning. \Acp{PF} are the most basic \ac{DS} stochastic primitives and take the form of logical facts, $a$, labelled with probabilities, $p$, such as $\probfact{p}{a}$; Each \ac{PF} represents a boolean random variable that is true with probability $p$ and false with probability $\co{p} = 1 - p$. A (consistent) combination of the \acp{PF} defines a \acf{TC} $t = \set{\probfact{p}{a}, \ldots}$ such that \franc{changed \acl{TC} $c$ to $t$ everywhere.}
133 133  
134 134 \begin{equation}
135   - \pr{C = c} = \prod_{a\in c} p \prod_{a \not\in c} \co{p}.
  135 + \pr{T = t} = \prod_{a\in t} p \prod_{a \not\in t} \co{p}.
136 136 \label{eq:prob.total.choice}
137 137 \end{equation}
138 138  
... ... @@ -379,7 +379,7 @@ The diagram in \cref{fig:running.example} illustrates the problem of extending p
379 379  
380 380 Given an ASP specification,
381 381 \remark{{\bruno Introduce also the sets mentioned below}}{how?}
382   - we consider the \emph{atoms} $a \in \fml{A}$ and \emph{literals}, $z \in \fml{L}$, \emph{events} $e \in \fml{E} \iff e \subseteq \fml{L}$ and \emph{worlds} $w \in \fml{W}$ (consistent events), \emph{\aclp{TC} } $c \in \fml{C} \iff c = a \vee \neg a$ and \emph{\aclp{SM} } $s \in \fml{S}\subset\fml{W}$.
  382 + we consider the \emph{atoms} $a \in \fml{A}$ and \emph{literals}, $z \in \fml{L}$, \emph{events} $e \in \fml{E} \iff e \subseteq \fml{L}$ and \emph{worlds} $w \in \fml{W}$ (consistent events), \emph{\aclp{TC} } $t \in \fml{T} \iff t = a \vee \neg a$ and \emph{\aclp{SM} } $s \in \fml{S}\subset\fml{W}$.
383 383  
384 384 Our path starts with a perspective of \aclp{SM} as playing a role similar to \emph{prime} factors. The \aclp{SM} of a specification are the irreducible events entailed from that specification and any event must be \replace{interpreted}{considered} under its relation with the \aclp{SM}.
385 385  
... ... @@ -515,48 +515,48 @@ where $\indepclass$ denotes both the class of \emph{independent} events $e$ such
515 515 \item Normalization of the weights.
516 516 \end{enumerate}
517 517  
518   -The ``extension'' phase, traced by equations (\ref{eq:prob.total.choice}) and (\ref{eq:weight.tchoice} --- \ref{eq:weight.events}), starts with the weight (probability) of \aclp{TC}, $\pw{c} = \pr{C = c}$, expands it to \aclp{SM}, $\pw{s}$, and then, within the equivalence relation from \cref{eq:equiv.rel}, to (general) events, $\pw{e}$, including (consistent) worlds.
  518 +The ``extension'' phase, traced by equations (\ref{eq:prob.total.choice}) and (\ref{eq:weight.tchoice} --- \ref{eq:weight.events}), starts with the weight (probability) of \aclp{TC}, $\pw{t} = \pr{T = t}$, expands it to \aclp{SM}, $\pw{s}$, and then, within the equivalence relation from \cref{eq:equiv.rel}, to (general) events, $\pw{e}$, including (consistent) worlds.
519 519  
520 520 \begin{description}
521 521 %
522 522 \item[Total Choices.] Using \eqref{eq:prob.total.choice}, this case is given by
523 523 \begin{equation}
524   - \pw{c} := \pr{C = c}= \prod_{a\in c} p \prod_{a \not\in c} \co{p}
  524 + \pw{t} := \pr{T = t}= \prod_{a\in t} p \prod_{a \not\in t} \co{p}
525 525 \label{eq:weight.tchoice}
526 526 \end{equation}
527 527 %
528   - \item[Stable Models.] Each \acl{TC} $c$, together with the rules and the other facts of a specification, defines a set of \aclp{SM} associated with that choice, that \remark{we denote by $\tcgen{c}$}{put this in the introduction, where core concepts are presented}.
  528 + \item[Stable Models.] Each \acl{TC} $t$, together with the rules and the other facts of a specification, defines a set of \aclp{SM} associated with that choice, that \remark{we denote by $\tcgen{t}$}{put this in the introduction, where core concepts are presented}.
529 529  
530   - Given a \acl{SM} $s \in \fml{S}$, a \acl{TC} $c$, and variables/values $\theta_{s,c} \in \intcc{0, 1}$,
  530 + Given a \acl{SM} $s \in \fml{S}$, a \acl{TC} $t$, and variables/values $\theta_{s,t} \in \intcc{0, 1}$,
531 531 \begin{equation}
532   - \pw{s, c} := \begin{cases}
533   - \theta_{s,c} & \text{if~} s \in \tcgen{c}\cr
  532 + \pw{s, t} := \begin{cases}
  533 + \theta_{s,t} & \text{if~} s \in \tcgen{t}\cr
534 534 0&\text{otherwise}
535 535 \end{cases}
536 536 \label{eq:weight.stablemodel}
537 537 \end{equation}
538   - such that $\sum_{s\in \tcgen{c}} \theta_{s,c} = 1$.
  538 + such that $\sum_{s\in \tcgen{t}} \theta_{s,t} = 1$.
539 539 %
540 540 \item[Classes.] \label{item:class.cases} Each class is either the inconsistent class, $\inconsistent$, or is represented by some set of \aclp{SM}.
541 541 \begin{description}
542 542 \item[Inconsistent Class.] The inconsistent class contains events that are logically inconsistent, thus should never be observed:
543 543 \begin{equation}
544   - \pw{\inconsistent, c} := 0.
  544 + \pw{\inconsistent, t} := 0.
545 545 \label{eq:weight.class.inconsistent}
546 546 \end{equation}
547 547 \item[Independent Class.] A world that neither contains nor is contained in a \acl{SM} describes a case that, according to the specification, shouldn't exist. So the respective weight is set to zero:
548 548 \begin{equation}
549   - \pw{\indepclass, c} := 0.
  549 + \pw{\indepclass, t} := 0.
550 550 \label{eq:weight.class.independent}
551 551 \end{equation}
552 552 \item[Other Classes.] The extension must be constant within a class, its value should result from the elements in the \acl{SC}, and respect the assumption \ref{assumption:smodels.independence} (\aclp{SM} independence):
553 553 \begin{equation}
554   - \pw{\class{e}, c} := \sum_{k=1}^{n}\pw{s_k, c},~\text{if}~\stablecore{e} = \set{s_1, \ldots, s_n}.
  554 + \pw{\class{e}, t} := \sum_{k=1}^{n}\pw{s_k, t},~\text{if}~\stablecore{e} = \set{s_1, \ldots, s_n}.
555 555 \label{eq:weight.class.other}
556 556 \end{equation}
557 557 and
558 558 \begin{equation}
559   - \pw{\class{e}} := \sum_{c \in \fml{C}} \pw{\class{e}, c}\pw{c}.
  559 + \pw{\class{e}} := \sum_{t \in \fml{T}} \pw{\class{e}, t}\pw{t}.
560 560 \label{eq:weight.class.unconditional}
561 561 \end{equation}
562 562 \remark{}{Changed from $\prod$ to $\sum$ to represent ``either'' instead of ``both'' since the later is not consistent with the ``only one stable model at a time'' assumption.}
... ... @@ -564,17 +564,17 @@ The ``extension'' phase, traced by equations (\ref{eq:prob.total.choice}) and (\
564 564 %
565 565 \item[Events.] \label{item:event.cases} Each (general) event $e$ is in the class defined by its \acl{SC}, $\stablecore{e}$. So, we set:
566 566 \begin{equation}
567   - \pw{e, c} := \frac{\pw{\class{e}, c}}{\# \class{e}} .
  567 + \pw{e, t} := \frac{\pw{\class{e}, t}}{\# \class{e}} .
568 568 \label{eq:weight.events}
569 569 \end{equation}
570 570 and
571 571 \begin{equation}
572   - \pw{e} := \sum_{c\in\fml{C}} \pw{e, c} \pw{c}.
  572 + \pw{e} := \sum_{t\in\fml{T}} \pw{e, t} \pw{t}.
573 573 \label{eq:weight.events.unconditional}
574 574 \end{equation}
575   - % \remark{instead of that equation}{if we set $\pw{s,c} := \theta_{s,c}$ in equation \eqref{eq:weight.stablemodel} here we do:
  575 + % \remark{instead of that equation}{if we set $\pw{s,t} := \theta_{s,t}$ in equation \eqref{eq:weight.stablemodel} here we do:
576 576 % $$
577   - % \pw{e} := \sum_{c\in\fml{C}} \pw{e, c}\pw{c}.
  577 + % \pw{e} := \sum_{t\in\fml{T}} \pw{e, t}\pw{t}.
578 578 % $$
579 579 % By the way, this is the \emph{marginalization + bayes theorem} in statistics:
580 580 % $$
... ... @@ -585,13 +585,13 @@ The ``extension'' phase, traced by equations (\ref{eq:prob.total.choice}) and (\
585 585  
586 586 % PARAMETERS FOR UNCERTAINTY
587 587 \begin{itemize}
588   - \item \todo{Remark that $\pw{\inconsistent, c} = 0$ is independent of the \acl{TC}.}
  588 + \item \todo{Remark that $\pw{\inconsistent, t} = 0$ is independent of the \acl{TC}.}
589 589 \item Consider the event $bc$. Since $\class{bc} = \indepclass$, from \cref{eq:weight.class.independent} we get $\mu\at{bc} = 0$.
590 590 \item \todo{Remark that equation \eqref{eq:weight.events.unconditional}, together with observations, can be used to learn about the \emph{initial} probabilities of the atoms, in the specification.}
591 591 \end{itemize}
592 592  
593 593  
594   -The $\theta_{s,c}$ parameters in equation \eqref{eq:weight.stablemodel} express the \emph{specification's} lack of knowledge about the weight assignment, when a single \acl{TC} entails more than one \acl{SM}. In that case, how to distribute the respective weights? Our proposal to address this problem consists in assigning an unknown weight, $\theta_{s,c}$, conditional on the \acl{TC}, $c$, to each \acl{SM} $s$. This approach allows the expression of an unknown quantity and future estimation, given observed data.
  594 +The $\theta_{s,t}$ parameters in equation \eqref{eq:weight.stablemodel} express the \emph{specification's} lack of knowledge about the weight assignment, when a single \acl{TC} entails more than one \acl{SM}. In that case, how to distribute the respective weights? Our proposal to address this problem consists in assigning an unknown weight, $\theta_{s,t}$, conditional on the \acl{TC}, $t$, to each \acl{SM} $s$. This approach allows the expression of an unknown quantity and future estimation, given observed data.
595 595  
596 596 % SUPERSET
597 597 Equation \eqref{eq:weight.class.other} results from conditional independence of \aclp{SM}.
... ... @@ -608,14 +608,14 @@ We continue with the specification from Equation \eqref{eq:example.1}.
608 608 \item[\Aclp{TC}.] The \aclp{TC}, and respective \aclp{SM}, are
609 609 \begin{center}
610 610 \begin{tabular}{ll|r}
611   - \textbf{\Acl{TC}} & \textbf{\Aclp{SM}} & \textbf{$\pw{c}$}\
  611 + \textbf{\Acl{TC}} & \textbf{\Aclp{SM}} & \textbf{$\pw{t}$}\
612 612 \hline
613 613 $a$ & $ab, ac$ & $0.3$\\
614 614 $\co{a} = \neg a$ & $\co{a}$ & $\co{0.3} = 0.7$
615 615 \end{tabular}
616 616 \end{center}
617 617 %
618   - \item[\Aclp{SM}.] The $\theta_{s,c}$ parameters in this example are
  618 + \item[\Aclp{SM}.] The $\theta_{s,t}$ parameters in this example are
619 619 $$
620 620 \theta_{ab,\co{a}} = \theta_{ac,\co{a}} = \theta_{\co{a}, a} = 0
621 621 $$
... ... @@ -628,9 +628,9 @@ We continue with the specification from Equation \eqref{eq:example.1}.
628 628 \begin{equation*}
629 629 \begin{array}{l|ll|r}
630 630 \stablecore{e}
631   - & \pw{s_k, c= \co{a}}
632   - & \pw{s_k, c= a}
633   - & \pw{\class{e}}=\sum_{c}\pw{\class{e},c}\pw{c}
  631 + & \pw{s_k, t= \co{a}}
  632 + & \pw{s_k, t= a}
  633 + & \pw{\class{e}}=\sum_{t}\pw{\class{e},t}\pw{t}
634 634 \\
635 635 \hline
636 636 \co{a}
... ... @@ -675,16 +675,19 @@ We continue with the specification from Equation \eqref{eq:example.1}.
675 675 & 1
676 676 \end{array}
677 677 \end{equation*}
678   - \item[Normalization.] To get a weight that sums up to one, we compute the \emph{normalization factor}. Since $\pw{\cdot}$ is constant on classes we have
  678 + \item[Normalization.] To get a weight that sums up to one, we compute the \emph{normalization factor}. Since $\pw{\cdot}$ is constant on classes,
679 679 \begin{equation*}
680 680 Z := \sum_{e\in\fml{E}} \pw{e}
681   - = \sum_{\class{e} \in\fml{E}/\sim} \frac{\pw{\class{e}}}{\#\class{e}},
  681 + = \sum_{\class{e} \in\class{\fml{E}}} \frac{\pw{\class{e}}}{\#\class{e}},
682 682 \end{equation*}
683   - that divides the weight function into a normalized weight:
  683 + that divides the weight function into a normalized weight
684 684 \begin{equation*}
685 685 \pr{e} := \frac{\pw{e}}{Z}.
686 686 \end{equation*}
687   -
  687 + such that
  688 + $$
  689 + \sum_{e \in \fml{E}} \pr{e} = 1.
  690 + $$
688 691 For the SBF example,
689 692 \begin{equation*}
690 693 \begin{array}{lr|r|rr}
... ... @@ -969,7 +972,7 @@ Considering the probabilities given in \cref{Figure_Alarm} we obtain the followi
969 972 \item The physical system might have \emph{latent} variables, possibly also represented in the specification. These variables are never observed, so observations should be concentrated \emph{somewhere else}.
970 973 \item Comment on the possibility of extending equation \eqref{eq:weight.events.unconditional} with parameters expressing further uncertainties, enabling a tuning of the model's \aclp{TC}, given observations.
971 974 \begin{equation*}
972   - \pw{e} := \sum_{c\in\fml{C}} \pw{e, c}\theta_c.
  975 + \pw{e} := \sum_{c\in\fml{T}} \pw{e, c}\theta_c.
973 976 \end{equation*}
974 977 \end{itemize}
975 978  
... ...