Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca HPSGs How its done, Examples, Examples, Examples Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca HPSG Feature Structure Descriptions – recall for pizza’s Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) A type hierarchy.... • ... states what kinds of objects we claim exist (the types) • ... organizes the objects hierarchically into classes with shared properties (the type hierarchy) • ... states what general properties each kind of object has (the feature and feature value declarations). Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Pizza Descriptions and Pizza Models How many pizza models (by definition, fully resolved) satisfy this description? Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Answer: 2 {<CRUST , thick> , <TOPPINGS , { <OLIVES , + > , <ONIONS, +> , <MUSHROOMS, −>}>} + > , <ONIONS, +> , <MUSHROOMS, +>}>} Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Pizza Descriptions and Pizza Models How many pizzas-in-the-world do the pizza models correspond to? Answer: A large, constantly-changing number. Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) ‘type’/‘token’ distinction applies to sentences as well Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Combining Constraints Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Combining Constraints Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Combining Constraints Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Combining Constraints Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Combining Constraints Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) A new theory of pizzas Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Combining Constraints Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Identity Constraints (tags) Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Combining Constraints Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Note Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Combining Constraints Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Why combine constraints? • The pizza example illustrates how unification can be used to combine information from different sources. • In our grammar, information will come from lexical entries, grammar rules, and general principles. Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Linguistic Application of Feature Structures: Making the Mnemonic Meaningful What do these CFG categories have in common? NP & VP: are both phrases N & V: are both words NP & N: are both ‘nouny’ VP & V: are both ‘verby’ Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) The Beginnings of our type hierarchy Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) A Feature for Part of Speech Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Type Hierarchy for Parts of Speech I Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Type Hierarchy for Parts of Speech II Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) A Feature for Valence Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Underspecification Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Another Valence Feature Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) SPR and Verbs Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) S and NP • We created a monster • our creation of a monster Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Type Hierarchy So Far Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Reformulating Grammar Rules 1 Which rules do these correspond to? Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Reformulating Grammar Rules 2 Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Reformulating the Grammar Rules 3 Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Advantages of the New Formulation • Subject-verb agreement is stipulated only once (where?) • Common properties of verbs with different valences are expressed by common features • Parallelisms across phrase types are captured Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Disadvantages of the New Formulation • We still have three head complement rules • We still have two head specifier rules • We only deal with three verb valences (which ones? what are some others?) • The non-branching rule does not really account for any empirical work • Others? Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Heads Intuitive idea: A phrase typically contains a word that determines its most essential properties, including – where it occurs in larger phrases, and – what is its internal structure This is called the head The term “head” is used both for the head word in a phrase and for all the intermediate phrases containing that word • NB: Not all phrases have heads Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Formalizing the Notion of Head • Expressions have a feature HEAD • HEAD’s values are of type pos • For HEAD values of type agr-cat, HEAD’s value also includes the feature AGR • Well-formed trees are subject to the Head Feature Principle Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) The Head Feature Principle • Intuitive idea: Key properties of phrases are shared with their heads • The HFP: In any headed phrase, the HEAD value of the mother and the head daughter must be identical. • Sometimes described in terms of properties “percolating up” or “filtering down”, but this is just metaphorical talk Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) A Tree is Well-Formed if … • It and each subtree are licensed by a grammar rule or lexical entry • All general principles (like the HFP) are satisfied. • NB: Trees are part of our model of the language, so all their features have values (even though we will often be lazy and leave out the values irrelevant to our current point). Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Question: Do phrases that are not headed have HEAD features? Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Reminder: Where We Are • Attempting to model English with CFG led to problems with the granularity of categories, e.g. – Need to distinguish various subtypes of verbs – Need to identify properties common to all verbs • So we broke categories down into feature structures and began constructing a hierarchy of types of feature structures. • This allows us to schematize rules and state crosscategorial generalizations, while still making fine distinctions. Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) But it’s still not quite right… • There’s still too much redundancy in the rules. • The rules and features encode the same information in different ways. Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Solution: More Elaborate Valence Feature Values • The rules just say that heads combine with whatever their lexical entries say they can (or must) combine with. • The information about what a word can or must combine with is encoded in list-valued valence features. – The elements of the lists are themselves feature structures – The elements are “cancelled” off the lists once heads combine with their complements and specifiers. Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Complements • This allows for arbitrary numbers of complements, but only applies when there is at least one. – Heads in English probably never have more than 3 or 4 complements – This doesn’t apply where Head-Complement Rule 1 would. • This covers lots of cases not covered by the old Head-Complement Rules 1-3. Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Question: What would the grammar change if English had postpositions instead of prepositions? Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Specifiers - Head Specifier Rule (version 1) Combines the rules expanding S and NP. In principle also generalizes to other categories. Question: Why is SPR list-valued? Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) QUESTION: Why are these rightbranching? That is, what formal property of our grammar forces the COMPS to be lower inthe tree than the SPR? Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Another Question… What determines the VAL value of phrasal nodes? ANSWER: The Valence Principle Unless the rule says otherwise, the mother’s values for the VAL features (SPR and COMPS) are identical to those of the head daughter. Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) More on the Valence Principle • Intuitively, the VAL features list the contextual requirements that haven’t yet been found. • This way of thinking about it (like talk of “cancellation”) is bottom-up and procedural. • But formally, the Valence Principle (like the rest of our grammar) is just a well-formedness constraint on trees, without inherent directionality Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) So far, we have: • Replaced atomic-valued VAL features with list-valued ones. • Generalized Head-Complement and Head-Specifier rules, to say that heads combine with whatever their lexical entries say they should combine with. • Introduced the Valence Principle to “cancel” things off the COMPS and SPR lists. Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) The Parallelism between S and NP • Motivation: – pairs like Chris lectured about syntax and Chris’s lecture about syntax. – both S and NP exhibit agreement The bird sings/*sing vs. The birds sing/*sings this/*these bird vs. these/*this birds • So we treat NP as the saturated category of type noun and S as the saturated category of type verb. Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Head Driven Phrase Structure Grammars (HPSGs) Question: Is there any other reason to treat V as the head of S? • In standard English, sentences must have verbs. (How about non-standard English or other languages?) • Verbs taking S complements can influence the form of the verb in the complement: I insist/*recall (that) you be here on time. • Making V the head of S helps us state such restrictions formally Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca
Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca Concluding Remarks NAÏVE Naive you are if you believe life favours those who aren't naive. Instructor: Nick Cercone - 3050 CSEB - nick@cse.yorku.ca