One aim
of artificial intelligence is to duplicate commonsense reasoning.
p.14"The
aim of artificial intelligence is to provide a computational model of intelligent behavior, most importantly, commonsense
reasoning."
We should not be afraid to look at events with probability in mind - it is probability after all that forms the structure
of reasoning.
p.15"this
book will try to communicate the idea that 'probability is not really about numbers; it is about the structure of reasoning,'
as Glenn Shafer recently wrote."
One way to plan in an uncertain environment is to use a fast but
efficient heuristic to generate possible outcomes of a model of the world. The influence diagram offers a compact
and agile model from which combinatorial searching can be performed. This activity, if properly focused on
relevant events that are likely to occur (goals, influences and constraints properly modeled), can serve as the foundation
of a modest but effective strategic plan.
p.306"Clearly, the only practical way of doing planning in an uncertain
domain is to generate portions of the decision tree on the fly from more economical forms of knowledge... The difficulty with
such a scheme is that the construction of any decision tree requires three diverse sources of knowledge, each organized by
a different set of principles:
1. Causal knowledge about how events influence each other in the
domain.
2. Knowledge about what action sequences are feasible in any given
set of circumstances.
3. Normative knowledge about how desirable the consequences are.
... Influence diagrams are an attempt to capture all three knowledge
sources in one graphical representation."
Information is used to make decisions, but clearly all sources of information are not alike. Deciding
which source to use (and which not to use) has a strong impart on the actual decision:
p.313"6.3.1 Information Sources and Their Values: It is generally
accepted that information is a useful commodity, that acting in an informed fashion is preferable to acting under ignorance.
This is why people accumulate information when it is available and purchase information when it is scarce. People also possess
strong intuition about whether one information source is more valuable (more reliable and pertinent) than another... The value
of any information source is defined as the difference between the utilities of two optimal strategies, one providing the
freedom of choosing different actions for different source outcomes, the other providing no such freedom. This criterion can
be used to rate the usefulness of various information sources and to decide whether a piece of information is worth acquiring."
Focusing attention is a way of acquiring information that is useful. The information we
acquire should be diagnostic in nature - just like an x-ray in terms of its ability to penetrate and show in high-contrast
terms what lies under the surface.
p.318"6.4.1 Focusing Attention: Control is the process
of scheduling the activation of information sources, both external (e.g., acquiring new input) and internal (e.g., invoking
rules or updating beliefs). Decision analysis provides a framework for scheduling all computational activities so as to focus
on specific goals - updating the belief in a target set of hypotheses, shifting attention to a new set, and terminating the
activity once we reach an acceptable level of confidence in a hypothesis.
The main reason for focusing attention on a select set of target hypotheses is to economize
the acquisition of new data. Let us imagine a subset S of the nodes (normally the leaves) that are known to be sensory or
observable nodes for a given problem domain (e.g., laboratory tests in medical diagnosis). In general, the instantiation of
any of these sensory nodes incurs a positive cost, and the utility of the information they convey might be insufficient to
justify this cost. Thus, it is important to decide which node in S should be instantiated first, based on the information
it contributes to the decision at hand, i.e., the target node. If utility information is available, then the value node naturally
is the target. If we lack utility information, we assign priorities to pending information sources based on their degree of
informativeness."
We might have to use decision theory to find the best technique. Where knowledge is missing we might
have to proceed towards secondary goals.
p.326"The task of controlling reasoning activities was formulated as that of finding an optimal
schedule for activating information sources. Decision theory provides a framework for assessing the knowledge and computations
needed to perform this optimization precisely. It turns out that the knowledge required is often unavailable... Subgoaling
strategies emerge as a reasonable compromise; they are computationally tractable... they still provide a focused way of acquiring
information."
