1. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6801 עיבוד שפות טבעיות - שיעור אחד עשר Unification (cont.) Semantics עידו דגן המחלקה למדעי המחשב אוניברסיטת בר אילן

2. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6802 Feature structures in the grammar CF grammar rules can be augmented with feature structures and with unification operations to express constraints on the constituents of a rule An example notation (the PATR-II formalism): β 0 β 1... β n {set of constraints} –Where the constraints have one of the following two forms: =(unify) atomic value =(unify) –e.g.S  NP VP =

3. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6803 Feature structures in the grammar S  NP VP {NP AGREEMENT} = {VP AGREEMENT} –This flight serves breakfast –These flights serve breakfast S  Aux NP VP {Aux AGREEMENT} = {NP AGREEMENT} –Does this flight serve breakfast? –Do these flights serve breakfast?

4. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6804 Feature structures in the grammar NP  Det Nominal = = –this flight vs. these flights

5. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6805 Feature structures in the grammar Lexical constituents receive their agreement features directly from the lexicon –Aux  does = sg = 3 –Det  this = sg –Det  these = pl

6. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6806 Feature structures in the grammar Verb  serve = pl Verb  serves = sg = 3 Non-lexical constituents(e.g. VPs) receive agreement values from their constituents VP  Verb NP =

7. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6807 Feature structures in the grammar Agreement (NP and Nominal) –Noun  flight = sg –Noun  flights = pl –Nominal  Noun =

8. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6808 Feature structures in the grammar For most grammatical categories, the features are copied from one child to the parent The child that provides the features is called the head of the phrase (the features are the head features) –VP  Verb NP = –NP  Det Nominal = = –Nominal  Noun =

9. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-6809 Subcategorization VP  Verb {VP SUBCAT} = INTRANS VP  Verb NP {VP SUBCAT} = TRANS VP  Verb NP NP {VP SUBCAT} = DITRANS

10. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68010

11. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68011 Semantics

12. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68012 Representing Meaning Up to now, we have not focussed 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.

13. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68013 Meaning Representations What can serve as a meaning representation... Anything that serves the core practical purposes of a program that is doing semantic processing: –Answering questions –Determining truth –Making inferences

14. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68014 semantic analysis הפעולה של השמת מבני משמעות לרכיבים לשוניים נקראת ניתוח סמנטי semantic analysis

15. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68015 The architecture Sentence Parsing Parse Tree Semantic Analysis Semantic Representation Syntactic Structure

16. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68016 Applications Ideally, applications would interact with the semantic representation of texts. Need a representation which is unambiguous, even though the text is ambiguous.

17. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68017 Problem of Ambiguity אין התאמה חח“ע בין משפט ובין הייצוג הסמנטי שלו (רב משמעות) וגם לא להפך:

18. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68018 Canonical Form Inputs that mean the same thing should have the same meaning representation! ייצוג משמעות אחיד לקלטים שונים נקרא canonical form מאפשר פישוט של תהליך ההסקה, אם המערכת צריכה להתמודד רק עם ייצוג יחיד.

19. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68019 Canonical Form John gave a car to Mary Mary was given a car by John give(John, Mary, a car) ∃ x ∃ y : give(x) ∧ agent(x, John) ∧ recipient(x,Mary) ∧ object(x,y) ∧ car(y)

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

21. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68021 FOPC – First Order Predicate Logic Meaning Structure of Language 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

22. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68022 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.

23. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68023 Predicate Argument Structure Predicate-like elements: –Verbs, VPs, prepositions, adjectives, some nouns. Argument-like elements: –Nouns, Nominals, NPs, etc

24. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68024 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)

25. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68025 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

26. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68026 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}

27. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68027

28. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68028

29. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68029 Determiners

30. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68030 Issues How to represent tense and aspect? Idioms (are not compositional)! Pragmatics (extra-syntactic)! Inference And much more…

31. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68031 Ambiguity Resolution Still have problem of ambiguity resolution: –Word sense disambiguation –Attachment ambiguity resolution

32. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68032 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.

33. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68033 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)

34. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68034 Solution look at the words around an ambiguous word in a large context window. Each word contributes potentially useful information about which sense of the ambiguous word is likely to be used with it. Apply a supervised learning mechanism

35. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68035 WordNet on-line lexical reference system, linguistically motivated nouns, verbs, adjectives, adverbs are organized into synonym sets (lexical concepts), contains a taxonomy of about 100,000 words

36. Syllabus Text Books Classes Reading Material Assignments Grades Links Forum Text Books 88-68036 WordNet semantic 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