Artificial Intelligence and Expert System CSE - 351

Transcription

1 welcome

2 Artificial Intelligence and Expert System CSE - 351

3 Artificial Intelligence and Expert System (CSE 351) Course Teacher: Amit Kumar Nath Lecturer Department of Computer Science & Engineering Bangladesh University of Business & Technology (BUBT)

4 Natural Language Processing

5 Contents 5 Natural Language Understanding Communication Fundamental of Language A Formal Grammar for a Fragment of English Semantic Analysis (Parsing) Natural Language Processing

6 Natural Language Understanding 6 Natural Language Understanding is one of the subfields of AI. It draws on ideas from philosophy and linguistics, as well as on techniques of logical and probabilistic knowledge representation and reasoning Natural Language Understanding requires an empirical investigation of actual human behavior

7 Communication 7 Communication is the intentional exchange of information brought about by the production and perception of signs drawn from a shared system of conventional sign. Human-Human Communication Speech, Gesture, etc, Human-Animal Communication Training by gesture or sign Human-Machine Communication Text Command, Speech command, Gesture, etc.

8 Communication (Cont.) 8 Communication involves three steps by the speaker: The intention to convey the Idea The mental generation of words and Their Physical Synthesis The Listener then has four steps Perception: Speech Recognition, OCR, Etc. Analysis: Syntactic interpretation (Parsing), Semantic interpretation, Pragmatic interpretation. Disambiguation and (based on knowledge about environment, current situation, about language use) Incorporation of the meaning

9 Fundamental of Language 9 Complex system of structured messages known as language that enables us to communicate most of what we know about the word. The means of express feelings to others is known language Speaker, Hearer (Listener), and Utterance as generic terms referring to any mode of communication. Word & Sentence, etc. Query, Inform, Request, Order, Acknowledgement, Promise, etc.

10 Fundamental of Language (Cont.) 10 A Formal Language is defined as a set of strings. Each string is concatenation of terminal symbols (words). Natural Language such as English, Bengali, have no strict definition but are used by a community of speakers. A Grammar is a finite set of rules that specifies a language. Natural Language have no official grammar.

11 Fundamental of Language (Cont.) 11 Most grammar rule formalisms are based on the ideas of phrase structure-that strings are composed of substrings called phrases Noun Phrase=NP, VB=Verb Phrase Sentence = NP+VP= (Article+Noun)+(Verb+Adjective) Example: The pen is good. Humans appear to be the only animals that use grammar to produce an unbounded variety of structured messages

12 A Formal Grammar for a Fragment of English 12 Lexicon system o : List of allowable words for a specific The words are grouped into the categories or parts of speech familiar to dictionary users:nouns, pronouns, verb, adjective, adverb, preposition, conjunction o The Grammar of : Generate good English using specific sentence formation rule.

13 Semantic Analysis (Parsing) 13 Parsing is the process of building a parse tree for an input strings. s NP VP Article Noun Verb Adjective The Pen is good

14 Natural Language Processing 14 Aim: Developing programs that understand natural language Problems: Infinite number of different sentences Ambiguity in natural language (Same word with several meaning)

15 Natural Language Processing (Cont.) 15 A program can understand a natural language If it behaves by taking a correct or acceptable action in response to the input, Example: Child demonstrate understanding if it responds with the correct answer to a question

16 Natural Language Processing (Cont.) 16 Level of knowledge: Phonological: knowledge of sound (Phoneme is the unit) Morphological: Basic unit of word (morpheme) friendly Syntactic: How words are put together to form correct sent.. Semantic: Meaning of word and phrase and sentence meaning Pragmatic: Sentence in different context and how the context effect meaning World: Language must include an understanding of the other person s belief and goal

17 Recommended Textbooks 17 [Negnevitsky, 2001] M. Negnevitsky Artificial Intelligence: A guide to Intelligent Systems, Pearson Education Limited, England, [Russel, 2003] S. Russell and P. Norvig Artificial Intelligence: A Modern Approach Prentice Hall, 2003, Second Edition [Patterson, 1990] D. W. Patterson, Introduction to Artificial Intelligence and Expert Systems, Prentice-Hall Inc., Englewood Cliffs, N.J, USA, [Lindsay, 1997] P. H. Lindsay and D. A. Norman, Human Information Processing: An Introduction to Psychology, Academic Press, 1977.

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