Castanet: Using WordNet to Build Facet Hierarchies

1. Castanet:Using WordNet to Build Facet Hierarchies Emilia Stoica and Marti HearstSchool of Information, Berkeley

2. Motivation Want to assign labels from multiple hierarchies

3. Fruit Apricot Flavor gingerroot Vegetables pepper Motivation Hot and Sweet Chicken: 1 pepper, 2 apricots, 1 pound chicken breast, 1 Tbsp gingerroot Meat Chicken

4. Castanet • Carves out a structure from the hypernym(IS-A) relations within WordNet • Produces surprisingly good results for a wide range of subjects • e.g., arts, medicine, recipes, math, news, bibliographical records

5. #1 cactus tuna food fish #2 fish bony fish WordNet Challenges • A word may have more than one sense -Fine granularity of word sense distinctions e.g., newspaper (#1) - daily publication on folded sheets newspaper (#3) - physical object - Ambiguity for the same sense

6. WordNet Challenges (cont.) • The hypernym path may be quite long (e.g., sense #3 of tuna has 14 nodes) • Sparse coverage of proper names and noun phrases (not addressed)

7. Algorithm Goals • Build a set of facet hierarchies • Balance depth and breadth • Avoid “skinny” paths • Don’t go too deep or too broad • Choose understandable labels • Disambiguate words • Currently a word can take on only one sense

8. Build core tree Augment core tree Select terms WordNet Divide into facets Remove top level categories Compress Tree Our Approach Documents

9. Select well-distributed terms from the collection Eliminate stopwords Retain only those terms with a distribution higher than a threshold (default: top 10%) 1. Select Terms Build core tree Augm. core tree Documents Select terms Comp. tree Remove top level categ. WordNet

10. Get hypernym path if term: - has only one sense, or - matches a pre-selected WordNet domain Adding a new term increases a count at each node on its path by # of docs with the term. Build core tree Augm. core tree Documents Select terms Comp. tree Remove top level categ. WordNet entity entity substance,matter substance,matter nutriment nutriment dessert dessert frozen dessert frozen dessert ice cream sundae sherbet,sorbet sherbet sundae 2. Build Core Tree • Build a “backbone” • Create paths from unambiguous terms only • Bias the structure towards appropriate senses of words

11. Merge hypernym paths to build a tree entity entity entity substance,matter substance,matter substance,matter nutriment nutriment nutriment frozen dessert dessert dessert dessert frozen dessert frozen dessert ice cream sundae sherbet,sorbet ice cream sundae sherbet,sorbet sherbet sundae sundae sherbet 2. Build Core Tree (cont.)

12. Build core tree Augm. core tree Documents Select terms Comp. tree Remove top level categ. WordNet 3. Augment Core Tree • Attach to Core tree the terms with more than one sense • Favor the more common path over other alternatives

13. Date (p1) Date (p2) entity abstraction substance,matter measure, quantity food, nutrient fundamental quality nutriment time period food calendar day (18) edible fruit (78) date date Choose this path since it has more items assigned Augment Core Tree (cont.)

14. Optional Step: Domains • To disambiguate, use Domains • Wordnet has 212 Domains • medicine, mathematics, biology, chemistry, linguistics, soccer, etc. • A better collection has been developed by Magnini 2000 • Assigns a domain to every noun synset • Automatically scan the collection to see which domains apply • The user selects which of the suggested domains to use or may add own • Paths for terms that match the selected domains are added to the core tree

15. Using Domains dip glosses: Sense 1: A depression in an otherwise level surface Sense 2: The angle that a magnet needle makes with horizon Sense 3: Tasty mixture into which bite-size foods are dipped dip hypernyms Sense 1 Sense 2 Sense 3 solid shape, form food => concave shape => space => ingredient, fixings => depression => angle => flavorer Given domain “food”, choose sense 3

16. Build core tree Augm. core tree Documents Select terms Comp. tree Remove top level categ. WordNet abstraction dessert frozen dessert sundae parfait sherbet 4. Compress Tree • Rule 1: • Eliminate a parent with fewer than kchildren unless it is the root or its distribution is larger than 0.1*maxdist dessert frozen dessert ice cream sundae parfait sherbet,sorbet sundae sherbet

17. Build core tree Augm. core tree Documents Select terms Comp. tree Remove top level categ. WordNet abstraction dessert sundae parfait sherbet 4. Compress Tree (cont.) • Rule 2: • Eliminate a child whose name appears within the parent’s name dessert frozen dessert sundae parfait sherbet

18. Divide into facets 5. Divide into Facets

19. entity substance,matter food,nutriment food stuff,food product ingredient,fixings flavorer flavorer herb herb sweetening sweetening parsley oregano sugar syrup parsley oregano sugar syrup Divide into facets 5. Divide into Facets(Remove top levels) Rule 1: Eliminate very general categories (e.g., entity, abstraction). If no paths are longer than threshold t, then done. Else: Rule 2: Undo first step. Then eliminate all top levels until the maximum length of any path in the resulting hierarchy is t.

20. Example: Recipes (3500 docs)

21. Castanet Output(shown in Flamenco)

22. Castanet Output

23. Castanet Output

24. Castanet Output

25. Castanet Output

27. Castanet Evaluation • This is a tool for information architects, so people of this type did the evaluation • We compared output on • Recipes • Biomedical journal titles • We compared to two state-of-the-art algorithms • LDA (Blei et al. 04) • Subsumption (Sanderson & Croft ’99)

28. Subsumption Output

29. Subsumption Output

30. Subsumption Output

31. Subsumption Output

32. LDA Output

33. LDA Output

34. LDA Output

35. Evaluation Method • Information architects assessed the category systems • For each of 2 systems’ output: • Examined and commented on top-level • Examined and commented on two sub-levels • Then comment on overall properties • Meaningful? • Systematic? • Likely to use in your work?

36. Evaluation (cont.) Sample questions for top level categories: - Would you add/remove/rename any category ? - Did this category match your expectations ? Sample questions for a specific category: - Would you add/move/remove any sub-categories ? - Would you promote any sub-category to top level ? General questions: - Would you use Castanet ? - Would you use LDA ? - Would you use Subsumption ? - Would you use list of most frequent terms ?

37. Evaluation Results • Results on recipes collection for “Would you use this system in your work?” • # “Yes in some cases” or “yes, definitely”: • Castanet: 29/34 • LDA: 0/18 • Subsumption: 6/16 • Baseline: 25/34 • Average response to questions about quality(4 = “strongly agree”)

38. Evaluation Results • Average responses for top-level categories • 4= no changes, 1 = change many • Average responses for 2 subcategories

39. Needed Improvements • Take spelling variations and morphological variants into account • Use verbs and adjectives, not just nouns • Normalize noun phrases • Allow terms to have more than one sense • Improve algorithm for assigning documents to categories.

40. Opportunities for Tagging • New opportunity: Tagging, folksonomies • (flickr, de.lici.ous) • People are created facets in a decentralized manner • They are assigning multiple facets to items • This is done on a massive scale • This leads naturally to meaningful associations

41. Conclusions • Castanet builds a set of faceted hierarchies by finding IS-A relations between terms using WordNet. • The method has been tested on various domains: • medicine, recipes, math, news, arts, bibliographical records • Usability study shows: • Castanet is preferred to other state-of-the art solutions. • Information architects want to use the tool in their work.

42. Learn More • Funding • This work supported in part by NSF (IIS-9984741) • For more information: • Stoica, E., Hearst, M., and Richardson, M., Automating Creation of Hierarchical Faceted Metadata Structures, NAACL/HLT 2007 • See http://flamenco.berkeley.edu