Week 3 - Reading

Chapter 7

7.1

  • The agent maintains a knowledge base, KB, which may initially contain some background knowledge.
  • Then we can expect it to cross the Golden Gate Bridge because it knows that that will achieve its goal. Notice that this analysis is independent of how the taxi works at the implementation level.
  •  This is called the declarative approach to system building. In contrast, the procedural approach encodes desired behaviors directly as program code.

7.2

  • The wumpus world is a cave consisting of rooms connected by passageways. Lurking somewhere in the cave is the terrible wumpus, a beast that eats anyone who enters its room.

Chapter 8

  • Propositional logic has a third property that is desirable in representation languages, namely, compositionality.
  •  For nondeductive tasks such as learning from experience, outcomes are necessarily dependent on the form of the representations used. 
  • The language of first-order logic, whose syntax and semantics we define in the next section, is built around objects and relations.
  • A logic can also be characterized by its epistemological commitments—the possible states of knowledge that it allows with respect to each fact.
  • The basic syntactic elements of first-order logic are the symbols that stand for objects, relations, and functions. The symbols, therefore, come in three kinds: constant symbols, which stand for objects; predicate symbols, which stand for relations; and function symbols, which stand for functions. 
  • An atomic sentence is true in a given model if the relation referred to by the predicate symbol holds among the objects referred to by the arguments.
  • Quantifiers let us do this. First-order logic contains two standard quantifiers, called universal and existential.
  • First-order logic includes one more way to make atomic sentences, other than using a predicate and terms as described earlier. We can use the equality symbol to signify that two terms refer to the same object.
  • One proposal that is very popular in database systems works as follows. First, we insist that every constant symbol refer to a distinct object—the so-called unique-names assumption. Second, we assume that atomic sentences not known to be true are in fact false—the closed-world assumption. 
  •  The knowledge engineer might already be an expert in the domain, or might need to work with real experts to extract what they know—a process called knowledge acquisition. 
  • The falsehood of this sentence can be determined independently of the rest of the knowledge base.

Chapter 12

  • Representing these abstract concepts is sometimes called ontological engineering.
  •  The general framework of concepts is called an upper ontology because of the convention of drawing graphs with the general concepts at the top and the more specific concepts below them.
  • Although interaction with the world takes place at the level of individual objects, much reasoning takes place at the level of categories.
  • We say that two or more categories are disjoint if they have no members in common. 
  • The values that we assign for these properties are called measures. 
  • It also can’t describe two actions happening at the same time—such as brushing one’s teeth while waiting for the tub to fill. To handle such cases we introduce an alternative formalism known as event calculus, which is based on points of time rather than on situations
  • The agents we have constructed so far have beliefs and can deduce new beliefs. Yet none of them has any knowledge about beliefs or about deduction. 
  • We begin with the propositional attitudes that an agent can have toward mental objects: attitudes such as Believes, Knows, Wants, Intends, and Informs. 
  • The syntax of first-order logic is designed to make it easy to say things about objects. Description logics are notations that are designed to make it easier to describe definitions and properties of categories.
  • Circumscription can be seen as a more powerful and precise version of the closed world assumption.
  • Truth maintenance systems also provide a mechanism for generating explanations.Technically, an explanation of a sentence P is a set of sentences E such that E entails P.
  • This is an example of a general technique called procedural attachment,whereby particular predicates and functions can be handled by special-purpose methods.

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