1. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6801 עיבוד שפות טבעיות - שיעור 11 Semantics אורן גליקמן המחלקה למדעי המחשב אוניברסיטת בר אילן

2. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6802 Representing Meaning Up to now, we have not focused at all on what things mean. How does one represent meaning? meaning representations: representations that bridge that gap from linguistic forms to knowledge of the world.

3. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6803 Meaning Representations What can serve as a meaning representation... Well anything that serves the core practical purposes of a program that is doing semantic processing: –Answering questions –Determining truth –Making inferences

4. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6804 semantic analysis הפעולה של השמת מבני משמעות לרכיבים לשוניים נקראת ניתוח סמנטי semantic analysis

5. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6805 The architecture Sentence Parsing Parse Tree Semantic Analysis Semantic Representation Syntactic Structure

6. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6806 Applications Applications will usually interact with the semantic representation level of texts. Need a representation which is unambiguous. הייצוג צריך להיות חד משמעי למרות שהקלט עצמו הוא רב משמעי.

7. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6807 Problem of Ambiguity אין התאמה חח“ע בין משפט ובין הייצוג הסמנטי שלו (רב משמעות) וגם לא להפך:

8. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6808 Canonical Form Inputs that mean the same thing should have the same meaning representation! המושג לקלטים שונים שלהם צריך להיות אותו ייצוג למשמעות נקרא canonical form המאפשר פישוט של תהליך ההסקה, אם המערכת צריכה להתמודד רק עם ייצוג יחיד.

9. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6809 Canonical Form John sold a car to Mary Mary was sold a car by John sell(John, Mary, a car) ∃ x,y : sell(x) ∧ agent(x, John), co- agent(x,Mary) ∧ object(x,y) ∧ car(y)

10. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68010 Problem of Many-to-Many Sentence in surface form Syntactic form Unambiguous Semantic Representation

11. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68011 Example Every bird lives on a tree Quantifier and word sense ambiguities. ∀ x bird(x) ∃ y : tree 1 (y) ∧ live_ on(x,y) ∃ y tree 1 (y): ∀ x bird(x)  live_on(x,y)

12. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68012 FOPC Meaning Structure of Language This choice of FOPC isn't completely arbitrary or driven by the needs of applications... Human languages: – display a basic predicate-argument structure –make use of variables –make use of quantifers –display a partially compositional semantics (sort of)

13. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68013 Predicate Argument Structure בכל השפות המדוברות מבנה הפרדיקט-ארגומנטים הוא הגרעין והיסוד של המשמעות בשפה. ההנחה הגסה הראשונה היא, אם כן, שבמשפט קיים יחס כלשהו בין המושגים המובעים במילים שבו וברכיביו השונים. אותו יחס הוא הבסיס לייצוג הסמנטי שיש למשפט. אחד התפקידים החשובים של התחביר הוא לתת מסגרת שתאפשר בנייה של אותו ייצוג, והייצוג צריך שיהיה לו קשר הדוק עם אותו מבנה תחבירי.

14. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68014 Predicate Argument Structure Predicate-like elements: –Verbs, VPs, prepositions, adjectives, some nouns. Argument-like elements: –Nouns, Nominals, NPs, etc

15. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68015 Example “John gave Mary the book” Giving(John, Mary, book) ∃ x,y: Giving (x) ∧ Giver(John,x) ∧ Givee(Mary,x) ∧ Given(y,x) ∧ Book(y)

16. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68016 Semantic Analysis Syntax driven semantics: –Most methods rely in some way on a prior or concurrent syntactic analysis (parse). Compositional Semantics: –at the core of most methods is the principle of compositionality which states that the meaning of the whole is based on the meaning of parts. –What are the parts? Words and syntactic constructs

17. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68017 Augmented CF Rules Verb  serves { x y ∃ e IsA(e, serving) ∧ server(e,y) ∧ served(e,x) } S  NP VP {VP.sem(NP.sem) } VP  Verb NP {Verb.sem(NP.sem)} MassNoun  Meat {Meat} ProperNoun  AyCaramba {AyCaramba}

18. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68018

19. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68019

20. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68020 Determiners

21. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68021 Issues How to represent tense and aspect? Idioms (are not compositional)! Pragmatics (extra-syntactic)! Inference And much more…

22. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68022 Ambiguity Resolution Still have problem of ambiguity resolution: –Word sense disambiguation –Attachment ambiguity resolution

23. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68023 WSD Problem: many words have different meanings or senses, i.e., there is ambiguity about how they are to be specifically interpreted (e.g., differentiate). Task: to determine which of the senses of an ambiguous word is invoked in a particular use of the word by looking at the context of its use.

24. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68024 Word Senses Bank –The rising ground bordering a lake, river, or sea –An establishment for the custody, loan exchange, or issue of money, for the extension of credit, and for facilitating the transmission of funds Title –Name/heading of a book, statue, work of art or music, etc. – Material at the start of a film –The right of legal ownership (of land) –The document that is evidence of the right –An appellation of respect attached to a person ’ s name –A written work (synecdoche: part stands for the whole)

25. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68025 Solution look at the words around an ambiguous word in a large context window. Each content word contributes potentially useful information about which sense of the ambiguous word is likely to be used with it. Apply a supervised learning mechanism

26. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68026 WordNet on-line lexical reference system, linguistically motivated nouns, verbs, adjectives, adjectives are organized into synonym sets (lexical concepts), contains a taxonomy of about 100,000 words

27. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68027 WordNet semantical relationships represented –Synonymy: similarity of work meaning, concepts as sets of words –Antonymy: dichotomy in meaning of words, used for organizing adjectives and adverbs –Hyponymy: IS-A relationships Superconcept to Subconcepts –Meronymy: Part-Of relationships between concepts –Morphological Relationships: used to reduce word forms