Agents - Embedded Intelligent Robotics - Lecture Slides, Slides of Robotics

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Agents that

Reason Logically

A knowledge-based agent

• A knowledge-based agent includes a knowledge base and an inference system.
• A knowledge base is a set of representations of facts of the world.
• Each individual representation is called a sentence.
• The sentences are expressed in a knowledge representation language.
• The agent operates as follows:
  1. It TELLs the knowledge base what it perceives.
  2. It ASKs the knowledge base what action it should perform.
  3. It performs the chosen action. 2

Examples of sentences The moon is made of green cheese If A is true then B is true A is false All humans are mortal Confucius is a human Docsity.com

• The Inference engine derives new sentences from the input and KB
• The inference mechanism depends on representation in KB
• The agent operates as follows:
  1. It receives percepts from environment
  2. It computes what action it should perform (by IE and KB)
  3. It performs the chosen action (some actions are simply inserting inferred new facts into KB).

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Knowledge Base

Inference Engine

Input from environment

Output (actions) Learning (KB update)

• Knowledge Level.
  • The most abstract level -- describe agent by saying what it knows.
  • Example: A taxi agent might know that the Golden Gate Bridge connects San Francisco with the Marin County.
• Logical Level.
  • The level at which the knowledge is encoded into sentences.
  • Example: Links(GoldenGateBridge, SanFrancisco, MarinCounty).
• Implementation Level.
  • The physical representation of the sentences in the logical level.
  • Example: “(Links GoldenGateBridge, SanFrancisco, MarinCounty)”

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KB can be viewed at different levels

review

Jargon file on “Hunt the Wumpus”

• WUMPUS /wuhm'p*s/ n. The central monster (and, in many versions, the name) of a famous family of very early computer games called “Hunt The Wumpus,” dating back at least to 1972
• The wumpus lived somewhere in a cave with the topology of a dodecahedron's edge/vertex graph
  • (later versions supported other topologies, including an icosahedron and Mobius strip).
• The player started somewhere at random in the cave with five “crooked arrows”;
  • these could be shot through up to three connected rooms, and would kill the wumpus on a hit - (later versions introduced the wounded wumpus, which got very angry).

Jargon file on “Hunt the Wumpus” (cont)

• Unfortunately for players, the movement necessary to map the maze was made hazardous not merely by the wumpus
  • (which would eat you if you stepped on him)
• There are also bottomless pits and colonies of super bats that would pick you up and drop you at a random location
  • (later versions added “anaerobic termites” that ate arrows, bat migrations, and earthquakes that randomly change pit locations).
• This game appears to have been the first to use a non-random graph-structured map (as opposed to a rectangular grid like the even older Star Trek games).
• In this respect, as in the dungeon-like setting and its terse, amusing messages, it prefigured ADVENT and Zork.
• It was directly ancestral to both.
  • (Zork acknowledged this heritage by including a super-bat colony.)
  • Today, a port is distributed with SunOS and as freeware for the Mac.
  • A C emulation of the original Basic game is in circulation as freeware on the net. (^8)

Agent in a Wumpus world: Percepts

• The agent perceives
  • a stench in the square containing the wumpus and in the adjacent squares (not diagonally)
  • a breeze in the squares adjacent to a pit
  • a glitter in the square where the gold is
  • a bump, if it walks into a wall
  • a woeful scream everywhere in the cave, if the wumpus is killed
• The percepts will be given as a five-symbol list:
  • If there is a stench, and a breeze, but no glitter, no bump, and no scream, the percept is [Stench, Breeze, None, None, None] (^) Docsity.com 10

The actions of the agent in Wumpus game are:

• go forward
• turn right 90 degrees
• turn left 90 degrees
• grab means pick up an object that is in the same square as the agent
• shoot means fire an arrow in a straight line in the direction the agent is looking. - The arrow continues until it either hits and kills the wumpus or hits the wall. - The agent has only one arrow. - Only the first shot has any effect. (^) Docsity.com 11

The Wumpus agent’s first step

Later

Representation, reasoning, and logic

• The object of knowledge representation is to express knowledge in a computer-tractable form , so that agents can perform well.
• A knowledge representation language is defined by: - its syntax, which defines all possible sequences of symbols that constitute sentences of the language. - Examples: Sentences in a book, bit patterns in computer memory. - its semantics , which determines the facts in the world to which the sentences refer. - Each sentence makes a claim about the world. - An agent is said to believe a sentence about the world.

The connection between

sentences and facts

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Semantics maps sentences in logic to facts in the world. The property of one fact following from another is mirrored by the property of one sentence being entailed by another.

Ontology and epistemology

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• Ontology is the study of what there is,
  • an inventory of what exists.
• An ontological commitment is a commitment to an existence claim.
• Epistemology is major branch of philosophy that concerns the forms, nature, and preconditions of knowledge.

Propositional logic

• Logical constants : true, false
• Propositional symbols : P, Q, S, ...
• Wrapping parentheses : ( … )
• Sentences are combined by connectives : ∧ ...and ∨ ...or ⇒...implies ⇔..is equivalent ¬ ...not (^) Docsity.com^20