1. INTRODUCTION TO ARTIFICIAL INTELLIGENCE Massimo Poesio LECTURE 6 The Cognitive Perspective: Generative Lexicon

2. 2 Sense Enumeration Lexicon (SEL) WordNet and similar resources are examples of SENSE ENUMERATION LEXICA Direct approach to handle polysemy is to allow the lexicon to have multiple listing of words, each annotated with a separate meaning or lexical sense. Widely accepted in both computational and theoretical linguistics.

3. 3 Sense Enumeration Lexicon (SEL) Example of Contrastive Senses bank 1 CAT= count-noun GENUS= financial-institution bank 2 CAT= count-noun GENUS= shore

4. Syntactic polysemy deals with polivalency (I), object deletion (II) and the general properties of argument expression (III). (I) a. Mary began to read the novel. b. Mary began reading the novel. c. Mary began the novel. (II) a. Mary ate (her meal) quickly. b. Mary devoured *(her meal) quickly. (III) a. John carved a doll (out of the wood). b. John carved the wood (into a doll). Verbal polysemy in sense enumeration lexica

5. (1)a. Mary doesn’t believe the book. b. John sold his books to Mary. (2)a. Eno the cat is sitting on yesterday’s newspaper. b. Yesterday’s newspaper really got me upset. (3)a. Mary is in Harvard Square looking for the Bach sonatas. b. We won’t get to the concert until after the Bach sonatas. (4)a. I have my lunch in the backpack. b. Your lunch was no longer today than it was yesterday. (5)a. The phone rang during my appointment. b. My next appointment is John. Nominal polysemy

6. 6 Nominal polysemy in sense enumeration lexica Newspaper Newspaper 2 CAT= count-noun GENUS= information Newspaper 1 CAT= count-noun GENUS= artefact

7. GENERATIVE LEXICON THEORY (Pustejovsky, 1991, 1995) Claim: the concepts associated with a word in a context are GENERATED by a process starting from lexical entries structured into QUALIA STRUCTUREs and involving GENERATIVE DEVICES such as TYPE COERCION and CO- COMPOSITION

8. 8 Generative lexicon theory: lexical entries A lexical entry in the generative lexicon consists of the following elements at least: Argument Structure  True Arguments  Default Arguments  Shadow Arguments  True Adjuncts Event Structure Qualia Structure  Formal  Constitutive  Telic  Agentive

9. Word meaning is structured on the basis of four generative factors, called qualia roles, that capture how humans understand objects and relations in the world and provide the minimal explanation for the linguistic behavior of lexical items. FORMAL : the basic category that distinguishes an object within a larger domain CONSTITUTIVE : the relation between an object and its constituent parts TELIC : the object’s purpose and function AGENTIVE : factors involved in the object’s origin or ‘coming to being’ QUALIA ROLES

10. 10 Qualia structures and argument polysemy Qualia Structure for novel novel const = narrative formal = book telic = reading agent = writing Qualia

11. 11 A generative device: type coercion Type Coercion  a lexical item or phrase is coerced to a semantic interpretation by a governing item in the phrase, without changing its syntactic type Mary began to read the novel Mary began reading the novel Mary began the novel Function Application with Coercion  different complement type of the verb  different interpretations of the verb that arise for the different complements

12. 12 Other generative devices Selective Binding  a lexical item or a phrase operates specifically on the substructure of a phrase, without changing the overall type in the composition a good knife: a knife that cuts well Co-composition  multiple elements within a phrase behave as functors, generating new non- lexicalized senses for the words in composition John baked the potato John baked the cake

13. (i) The Generative Lexicon Theory proposes to separate the characteristic property ( FORMAL role ) from the functional aspect ( TELIC role ) of the notion of food. Food is a concept making reference to distinct and orthogonal facets of knowledge, each expressing a different explanation of this concept. We can represent our analytic knowledge associated with food by conjoining or unifying ‘orthogonal’ values from and qualia roles. Such a structure is called a unified type. This method permits a general strategy for creating increasingly specific concepts with conjunctive properties. (Unified types can be seen as structured by orthogonal dimensions or perspectives, rather than as inheriting properties from multiple parents in a homogeneous property structure.) EXAMPLE: FOOD

14. A schematic description of a lexical item a: a ARGSTR = ARG1= x ……… QUALIA = CONST = what x is made of FORMAL = what x is TELIC = function of x AGENTIVE = how x came into being QUALIA ROLES

15. Schematic Representation food ARGSTR = [ ARG 1 = x:substance ] QUALIA = FORMAL = x TELIC = eat ( e,y,x ) Let P F and Q T be the values associated with the FORMAL and TELIC qualia respectively and analyze the orthogonal values of the qualia roles as logical conjunction: λx[P F (x)  Q T (x)]. For the interpretation of the noun food, this would give the expression: λx[substance F (x)  λyλe [eat T (e,y,x)]]

16. A dot object is a deeper structure relating the apparently contradictory senses of the word. For each sense pair there is a relation that ‘connects’ the senses in a well-defined way. The dot object is characterized as: - a Cartesian type product of n types (the product τ 1 x τ 2, of types τ 1 and τ 2, each denoting sets, is the ordered pair, where t 1 ε τ 1, t 2 ε τ 2 ) -with some additional constraints: there exists a relation R between the elements of τ 1 and τ 2, namely, R(t 1, t 2 ). This relation must be seen as part of the definition of the semantics for the dot object. NOMINAL POLYSEMY

17. Type combinations included in the broad range of complex types encountered in natural language: a. phys_obj  info : e.g., book, record b. event  event : e.g., construction, examination c. event  question : e.g., exam d. event  food : e.g., lunch, dinner e. event  human : e.g., appointment For each of these type products, there is a unique relation, R i, that structures the types. For example, nouns such as book or record, are structured by a containment relation R (container-like concepts). This containment relation -hold(x,y)- must be encoded directly into the semantics of the concept as the FORMAL quale value.

18. The lexical structure for newspaper as a dot object is represented as follows: newspaper ARGSTR = ARG1 = y:information ARG2 = x:phys_obj QUALIA = information  phys_obj FORM = hold(x,y) TELIC = read(e,w,x  y) AGENT = write(e,v,x  y) This translates to the following logical expression: λx  y  e   v [newspaper (x: physobj  y : info )  hold(x,y)  λwλe [read (e,w,x  y)  [write(e;v,x  y)]]

19. The lexical structure for book as a dot object is represented as follows: book ARGSTR = ARG1 = y:information ARG2 = x:phys_obj QUALIA = information  phys_obj FORM = hold(x,y) TELIC = read(e,w,x  y) AGENT = write(e,v,x  y) This translates to the following logical expression: λx  y  e   v [book (x: physobj  y : info )  hold(x,y)  λwλe [read (e,w,x  y)  [write(e;v,x  y)]]

20. REFERENCES Pustejovsky, J. (1995). The generative Lexicon. Cambridge, MA: MIT Press.