CC 2007, 2011 attribution R.B. Allen Languages: Natural and Formal.
Transcript of CC 2007, 2011 attribution R.B. Allen Languages: Natural and Formal.
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CC 2007, 2011 attribution R.B. Allen
Languages: Natural and Formal
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CC 2007, 2011 attribution R.B. Allen
Language
• Definition– In math and computer science:
• A lexicon & rules for combining terms from the lexicon
– In common use:• Structured verbal interaction between people• Any structured interaction such as “The
Language of Film”
• Are computer languages a model for human natural language?
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CC 2007, 2011 attribution R.B. Allen
Wide Variability among Natural Languages
• Sentence Structure– SVO (Subject-Verb-Object) (English, Chinese)– OVS (Gaelic/Celtic)– SVO (Hindi, Japanese, Hopi)
• Written– Ideographic (Chinese), – Syllabic (Thai), – Alphabetic (English)
• Spoken– Tonal (Chinese) – Non-tonal (English)
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CC 2007, 2011 attribution R.B. Allen
Layers of Natural Language
• Words– Morphology, Orthography, Phonetics, Phonology
• Syntax – Phrase and sentence structure based on parts of speech
• Semantics – Literal meaning
• Pragmatics/Discourse – Uses beyond the literal meaning
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CC 2007, 2011 attribution R.B. Allen
Grammars
• Grammars are most often associated with modeling syntax though semantic grammars are also possible. In the broadest sense, grammars are rules for languages
• The most general grammars are “context-free”. That is, the structure does not depend of the context.
• The grammars used for natural language syntax are usually “constituent grammars”. That is they identify the relationship of the components (constituents) of the phrase.
• Grammars taught in grade school are “descriptive” grammars. Grammars in the formal analysis of language are “prescriptive” and usually “generative”.
• Grammars are usually defined by rules, but statistical transition networks are also used to model the structure of language.
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CC 2007, 2011 attribution R.B. Allen
Modeling Natural LanguageSyntax with Grammars
• Rewrite (or production) rules (phrase-structure grammar)
• A very simple example of rewrite rules
S NP+VPNP N, Adj+N,
VP V, V+NP
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CC 2007, 2011 attribution R.B. Allen
Parsing
• Can we identify the grammatical structure of a given statement? • Parsing is the basis of syntax checking for computer program
compilers.• A parse tree is structure of a given statement given
– a lexicon with parts-of-speech– a grammar
• A very simple sample parse tree shown at the right. This hasa Verb Phrase with a Direct Object.This Direct Object is itself a NounPhrase.
• Difficulties: Garden path sentences– “The man who hunts ducks out on weekends”
• Many algorithms have been developed for parsing,
SNP VP
N V
NP
Adj
Adj N
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CC 2007, 2011 attribution R.B. Allen
Psycholinguistics
• How do people process and learn language?• Chomsky’s claims for formal (discrete)
grammars:• All natural languages are context free• Children have grammatical rules wired in:
– “I goed to the store.”• Competence vs. performance
• People know what is grammatically correct even if they make errors.
• Transformational grammars describe rules for re-arranging of structure such as forming a question from a declarative sentence.
• An alternative to discrete (formal) grammars is statistical (approximate) grammars. These can be learned by association.
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CC 2007, 2011 attribution R.B. Allen
Modeling Syntax with Statistical Models
• While most grammars are a rule-based representation, a statistical representation of language may m capture structure more flexibly.
• In particular, Markov models can describe the transitions between different parts of speech. For instance, the Nouns are often followed by Verbs but Adjectives are rarely followed by Verbs.
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CC 2007, 2011 attribution R.B. Allen
Words
• What exactly is a word? (also matters for the design of search engines)– Sail-boat, Pennsylvania, 555-1212, F-16
• Definitions of words– Why aren’t the definitions of words in dictionaries all
the same?– Are exact definitions of words possible?
• Across time, across groups– How do words evolve in meaning?
• Sometimes by radial categories (that is, often by metaphor)
• What is the relationship between concepts and words?
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CC 2007, 2011 attribution R.B. Allen
Beyond Traditional Dictionaries:WordNet and FrameNet
• WordNet http://wordnet.princeton.edu/
– Shows hierarchical relationships for dictionary terms. Very loosely, this can be thought of as an ontology.
• FrameNet http://framenet.icsi.berkeley.edu/
– Shows the elements usually associated with a concept.
– For verbs show the relationship among concepts. For instance “to give” implies that there is a gift, a gifter, and a giftee.
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CC 2007, 2011 attribution R.B. Allen
Semantics
• Very different surface structures can have similar semantics.
• The semantics of natural language is often judged by the meaning and relationship of the components. Subjective and contextualized meaning is considered as pragmatics which we will discuss later.
• The semantics of statements in a computer programming language (i.e., a program) can be determined from its behavior.
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CC 2007, 2011 attribution R.B. Allen
Representing Semantics
• Semantic grammars– Even with different surface structure, can
we develop a standard representation for the meaning.
• Interlingua– A common representation for meaning
across languages. This could be useful for translation.
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CC 2007, 2011 attribution R.B. Allen
Pragmatics: Social Uses of Language
• Pragmatics extends the literal semantics to consider other ways language is used.– Referential
• Conveys information about some real phenomenon • This is what we think about as normal language use
– Expressive• describes feelings of the speaker
– Conative• attempts to elicit some behavior from the addressee
– Phatic• builds a relationship between both parties in a conversation
– Meta-lingual• self-references
– Poetic• focuses on the text independent of reference
from R. Jakobson
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CC 2007, 2011 attribution R.B. Allen
Discourse
• Sentences form macro-structures or super-structures of meaning. This includes structured language such as argumentation, negotiation, news, narrative, and explanations.
• What are the components (elements) and structure of discourse. For instance, structuring messages to make it clear for listeners.
• Given-New Bill (a person you know) went to the store (is in a new location)
• Theme-RhemeWhen in Rome (theme), do as the Romans do (rheme)
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CC 2007, 2011 attribution R.B. Allen
Argumentation
• Toulmin has proposed a general structure for arguments
• There are a lot of complex structured verbal interactions– Legal arguments– Design rationale– Negotiations
ClaimGrounds
RebuttalEvidence
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CC 2007, 2011 attribution R.B. Allen
Explanations and Causation
• An explanation consists of– Two types of phenomena being explained
• Causal antecedents– How do we explain the American Civil War?
• Sub-processes– How does a gasoline engine work?
– Background for the person receiving the explanation needs to be considered.
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CC 2007, 2011 attribution R.B. Allen
Stories and Narrative
• (Goals + Events + Resolution) + Characters• Many stories seem highly structured
– Some stories seem so structured that they have been described as “story grammars”. This is most notably true of Russian Fairy Tales
• Many stories also reflect familiar human quandaries– “Romeo and Juliet”
• Interactive and dynamic narrative (useful in games)– Could we become a player in an interactive
“Romeo and Juliet”?
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CC 2007, 2011 attribution R.B. Allen
Conversation
• Conversation adds a social and interactive component to language
• Conversational norms (Maxims) • Truthful, informative, relevant, clear• But these are routinely violated.
• e.g. shaggy dog stories.
• Managing conversations– Opening / Closing– Turn taking
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How close to Passing the Turing Test?
Chatterbots
IBM “Watson” plays Jeopardy.
CC 2007, 2011 attribution - R.B. Allen
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CC 2007, 2011 attribution R.B. Allen
Natural Language Processing (NLP)
We will revisit natural language in a few weeks when we look at the use of natural language in information systems.
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Formal Languages
• Programming languages• High-level languages (e.g., C++) are
built to simplify the use of low-level machine language
• Debugging tools typically check syntax but not semantics
CC 2007, 2011 attribution - R.B. Allen