1. Ch.11 Features and Unification Ling 538, 2006 Fall Jiyoung Kim

2. Content I. Feature Structures II. Unification of Feature Structures III. Discussion

3. I. Feature Structures - terms Feature Structure. Sets of feature-value pairs. Represented as - AVMs (Attribute-Value Matrix) - DAGs(Directed Acyclic Graphs) (  features can have feature structures as their values!) Feature path A list of features through a feature structure leading to a particular value Reentrant structures Shared feature structures

4. I. Feature Structures - ex CAT NP AGREEMENT NUMBER SG PERSON 3 AGREEMENT CAT NP NUMBER PERSON SG 3 Feature structure Feature path to SG:

5. I. Feature Structures - ex HEAD CAT S NUMBER PERSON SG 3 Shared Values AGREEMENT SUBJECT

6. II. Unification of Feature Structures - term Unification Merging the information content of two structures Rejecting the merger of structures that are incompatible - implemented as a binary operator

7. II. Unification of Feature Structures - ex U: Unification operator EX 1) [NUMBER SG] U [NUMBER SG] = [NUMBER SG] EX 2) [NUMBER SG] U [NUMBER PL] FAILS!

8. II. Unification of Feature Structures - ex EX 3) [NUMBER SG] U [PERSON 3] = NUMBER SG PERSON 3 EX 4) AGREEMENT  NUMBER SG PERSON 3 SUBJECT [AGREEMENT  ] U SUBJECT AGREEMENT PERSON 3 NUMBER SG = AGREEMENT  NUMBER SG PERSON 3 SUBJECT [AGREEMENT  ]

9. II. Unification of Feature Structures - ex EX 5) AGREEMENT  NUMBERSG PERSON3 SUBJECTAGREEMENT  UAGREEMENTNUMBERSG PERSON3 SUBJECTAGREEMENTNUMBERPL PERSON3 Fails!

10. III. Discussion [+N] Specific (Proper) HumanCount HumanWater MasAnim BoyGirlChickenSchool RoosterHen (Masc) MasLondon JohnJane + + + + + + + +- - - - - - - - Are features independent each other? (incomplete) classificatory tree - noun

11. III. Discussion What are the concepts? Why do we need those? –to express syntactic constraints that would be difficult to express using the mechanisms of context-free grammars only How are they implemented? –CopyDAG, Types and Inheritance,..

12. Thank you!