Natural Language Sections

What the Speaker Speaks §Intention l S wants H to believe P §Generation l S chooses the words, W to convey the concept §Synthesis l S utters the words, W to H

Speaker

What the Hearer Hears §Perception l H perceives W’ (if we are lucky W’=W) §Analysis l H infers that W’ has possible meanings P1…Pn words and phrases can have several meanings §Disambiguation l H infers that S intended to convey Pi §Incorporation l H decides to believe Pi (or not)

Hearer

Encoded Message Model §One theory assumes that the problems are most easily understood if we can split them up into: l Encoding problems, in which the speaker does not correctly convert the proposition into a message l Transmission problems like noise l Decoding problems, causing the hearer to believe an unintended message

Situated Language Model §A more modern approach believes that the meaning of a message depends on both the words and the situation in which the words are used. l A toaster is hot if it is warm to the touch, selling well, or stolen. l What if the speaker assumes that hearer is in a context he is not in?

Telepathic Communication §Skip over the nasty problems of noise and mispronunciation and incorrect encoding (for now) so we can understand 3 simpler problems: l Naming -- When I refer to “the monster” am I talking about the same one you are? l Correlation -- If I am seeing the head of an elephant is it the same elephant whose tail you see? l Independent Knowledgebases -- Communication might not be free and instantaneous

Telepathic Communication

In Wumpus World §Robot Slave l I feel a breeze l Nothing is at 2 1 l In 2 2, I feel a breeze l OK. I will stay here. l OK, I am facing 1 3 l In 1 3 I feel breeze and smell stench and see glitter l... §Master l Go to 2 1 l Go North l A pit is to the East l Turn left l Go forward l Grab the gold l...

What the robot had to do §kb.tell(percept.getPercept(), timenow); §words <= percept.speechPart(); §msg <= words.disambig(); §if (msg.isCommand()) msg.doAction(); §if (msg.isStatement()) { l kb.tell(msg); l action = kb.askNextAct(percept,timenow); §return(percept + action)

A Formal Subset of English §Lexicon: The universe of all words we will use and their categories §Grammar: Valid combinations of words into phrases and sentences

Lexicon §Noun  stench | breeze | glitter |... §Verb  is | see | smell | shoot |... §Adjective  right | left | east | smelly |... §Adverb  right | left | here | there | ahead |... §Pronoun  me | you | it |... §Name  Jim | Mark |... §Article  the | a | an |... §Preposition  to | in | on | near |... §Conjunction  and | or | but |... §Digit  0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

Grammar of pseudo-English in Backus-Naur Form (BNF) S  NP VPI + feel a breeze | S Conjunction SI feel a breeze + and + I smell a wumpus NP  PronounI | Nounpits | Article Nounthe + wumpus | Digit Digit3 4 | NP PPthe wumpus + to the east | NP RelClausethe wumpus + that is smelly

Grammar (cont.) VP  Verbstinks | VP NPfeel + a breeze | VP Adjectiveis + smelly | VP PPturn + to the east | VP Adverbgo + ahead PP  Preposition NPto + the east RelClause  that VPthat + is smelly

Railroad Diagram for S Noun PhraseVerb Phrase ConjunctionSS Notice that S is recursive

Parsing pseudo-English

Parse Tree

Conclusion §Natural language processing is hard l needs knowledge of a shared grammar l hard to integrate knowledge from another kb l hard to communicate goals, beliefs, plans §Speech is an attempt to get another agent to believe something or do something §Grammars are a useful tool for regularizing communications to avoid misunderstanding