1. Lexicografie computationala Feb., 2012 Anca Dinu University of Bucharest

2. Intoducere Lexicologia computationala este utilizarea calculatoarealor in studiul lexiconului (teoretic). Lexicografia computationala inseamna crearea de machine readable dictionaries (MRD) (practic). Se folosesc uneori ca sinonime.

3. Introducere MRD sunt resurse esentiale pentru NLP (Summarization, question answering, inference, etc). Importanta lor este si mai mare pentru limbile cu o morfologie bogata. Au o componenta generativa care construieste formele inflectionale pornind de la leme si reguli de formare.

4. Directii in CL Adnotare de corpus (de obicei in XML): Markup Languages permit crearea de corpusuri adnotate standardizat din care apoi se pot extrage automat sau semi-automat (Corpus Pattern Analysis) date pentru crearea de lexicoane (structura argumentala, roluri tematice, etc.)

5. Directii in CL Creare Lexical Knowledge Bases (LKBs). Contin aceleasi informatii ca un dictionar printat, avand in plus informatii sintactice, semantice si relationale (ontologii)Lexical Knowledge Bases Ex: WordNet; FrameNetWordNetFrameNet

6. WordNet Nouns, verbs, adjectives and adverbs are grouped into sets of cognitive synonyms (synsets), each expressing a distinct concept. Synsets are interlinked by means of conceptual-semantic and lexical relations. The resulting network of meaningfully related words and concepts can be navigated with the browser.

7. Annotation: principii generale Annotation schemata should focus on a single coherent theme: Different linguistic phenomena should be annotated separately over the same corpus Annotations must be consistent with each other: Unification and merging of multiple annotation is necessary (standard XML)

8. Examples of Semantic Annotation Predicators and their named arguments: [The man] agent painted [the wall] patient. Anaphors and their antecedents: [The protein] inhibits growth in yeast. [It] blocks production... Acronyms and their long forms: [Platelet-derived growth factor] (known as [pdgf]) impacts... Semantic Typing of entities: [The man] human fired [the gun] firearm.

9. Probleme cu LKB existente Organizarea traditionala a lexicoanelor este statica, i.e. presupune ca intelesul unui cuvant pote fi definit exhaustiv printr-o enumerare a sensurilor (tip lista). In consecinta, cand o problema de interpretare a limbajului natural se loveste de ambiguitate lexicala, sistemul incearca sa selecteze cea mai apropiata definitie din lista oferita de lexicon

10. Probleme cu LKB existente 2 dezavantaje: Trebuie specificate a priori “toate” contextele posibile in care poate aparea un cuvant; in caz contrar, rezulta acoperire incompleta; Nu se poate explica/prezice utilizarea creativa a cuvintelor in contexte noi

11. Solutie : Generative Lexicon (GL) James Pustejovsky: 1995 (cartea Generative lexicon), 2001, 2005 De citit pt data viitoare articolul “Type Theory and Lexical Decomposition”

12. Language meaning is compositional. Compositionality is a desirable property of a semantic model. Many linguistic phenomena appear non- compositional. GL exploits richer representations and fixes the holes in the compositionality model. Assumptions for GL

13. Exemple de fapte lingvistice care par de natura non-compozitionala intensionality (think), binding (she), quantification (most), interrogatives (who), focus (only), and presuppositions (the king of France).

14. The meaning of a complex expression is determined by its structure and the meanings of its constituents. Questions... 1. What is the nature of the structure? 2. What is the meaning of a constituent? 3. What counts as a constituent? Compositionality

15. (1) a. Mary began [to eat her breakfast]. b. Mary began [eating her breakfast]. c. Mary began [her breakfast]. (2) a. Mary enjoyed her beer. b. John enjoys his coffee in the morning. c. Bill enjoyed the movie. Challenges to Simple Compositionality

16. (3)a. The woman baked a potato in the oven. b. The woman baked a cake in the oven. (4) a. John swept. b. John swept the floor. c. John swept the dirt into the corner. d. John swept the dirt off the sidewalk. e. John swept the floor clean. f. John swept the dirt into a pile.

17. Challenges to Simple Compositionality shovel, rake, shave, weed. (5) a. John whistled. b. John whistled at the dog. c. John whistled a tune. d. John whistled a warning. e. John whistled his appreciation. f. John whistled to the dog to come. yell, snap, whisper.

18. (6) Externally Caused Events: break, etc. a. The vase broke. b. Mary broke the vase. c. The storm broke the window. (7) Internally Caused Events (unacusatives): decay, bloom, etc. a. The flowers bloomed early. b. *The gardener bloomed the flowers. Challenges to Simple Compositionality

19. 1. What is the nature of the function? 2. What does it apply to; i.e., what can be an argument? 1. John loves Mary. 2. love(Arg1,Arg2) 3. Apply love(Arg1,Arg2) to Mary 4. love(Arg1,Mary) 5. Apply love(Arg1,Mary) to John 6. love(John,Mary) Compunere = aplicare de functii

20. Lambda Calcul (a) e is a type. (b) t is a type. (c) If a and b are types, then a -> b is a type. A simple type tree: t e e->t Function Application: If α is of type a, and β is of type a -> b, then β(α) is of type b.

21. Lambda calcul data viitoare