1. The Descent of Hierarchy, and Selection in Relational Semantics*
Barbara Rosario, Marti Hearst, Charles Fillmore
UC Berkeley
*with apologies to Charles Darwin

2. Noun Compounds (NCs) Technical text is rich with NCs
Open-labeled long-term study of the subcutaneous sumatriptan efficacy and tolerability in acute migraine treatment.
Any sequence of nouns that itself functions as a noun
asthma hospitalizations
health care personnel hand wash

3. NCs: 3 computational tasks
Identification
Syntactic analysis (attachments)
[Baseline [headache frequency]]
[[Tension headache] patient]
Our Goal: Semantic analysis
Headache treatment  treatment for headache
Corticosteroid treatment  treatment that uses corticosteroid

4. Descent of Hierarchy Idea: Hypothesis:
Use the top levels of a lexical hierarchy to identify semantic relations
Hypothesis:
A particular semantic relation holds between all 2-word NCs that can be categorized by a lexical category pair.

5. Outline Related work Linguistic motivation Lexical Hierarchy: MeSH
Labeling NC relations
Method and results
Discussion of ambiguity

6. Related work (Semantic analysis of NCs)
Rule-based
Finin (1980)
Detailed AI analysis, hand-coded
Vanderwende (1994)
automatically extracts semantic information from an on-line dictionary, manipulates a set of handwritten rules classes, 52% accuracy
Probabilistic
Lauer (1995):
probabilistic model, 8 classes, 47% accuracy
Lapata (2000)
classifies nominalizations into subject/object classes, 80% accuracy

7. Related work (Semantic analysis of NCs)
Lexical Hierarchy
Barrett et al. (2001)
WordNet, heuristics to classify a NC given the similarity to a known NC
Rosario and Hearst (2001)
MeSH, Neural Network. 18 classes, 60% accuracy
Relations pre-defined

8. Linguistic Motivation
Semantics of the NCs: head-modifier relationship
Head noun has argument structure
Meaning of the head noun determines what kinds of things can be done to it, what it is made of, what it is a part of…

9. Linguistic Motivation (cont.)
Material + Cutlery  Made of
steel knife, plastic fork, wooden spoon  
Food + Cutlery  Used on
meat knife, dessert spoon, salad fork 
Profession + Cutlery  Used by
chef's knife, butcher's knife

10. Outline Related work Linguistic motivation Lexical Hierarchy: MeSH
Labeling NC relations
Method and results
Discussion of ambiguity

11. The lexical Hierarchy: MeSH
Tree Structures
1. Anatomy [A]
2. Organisms [B]
3. Diseases [C]
4. Chemicals and Drugs [D]
5. Analytical, Diagnostic and Therapeutic Techniques and Equipment [E]
6. Psychiatry and Psychology [F]
7. Biological Sciences [G]
8. Physical Sciences [H]
9. Anthropology, Education, Sociology and Social Phenomena [I]
10. Technology and Food and Beverages [J]
11. Humanities [K]
12. Information Science [L]
13. Persons [M]
14. Health Care [N]
15. Geographic Locations [Z]

12. The lexical Hierarchy: MeSH
1. Anatomy [A] Body Regions [A01]
2. [B] Musculoskeletal System [A02]
3. [C] Digestive System [A03]
4. [D] Respiratory System [A04]
5. [E] Urogenital System [A05]
6. [F] ……
7. [G]
8. Physical Sciences [H]
9. [I]
10. [J]
11. [K]
12. [L]
13. [M]

13. Descending the Hierarchy
1. Anatomy [A] Body Regions [A01] Abdomen [A01.047]
2. [B] Musculoskeletal System [A02] Back [A01.176]
3. [C] Digestive System [A03] Breast [A01.236]
4. [D] Respiratory System [A04] Extremities [A01.378]
5. [E] Urogenital System [A05] Head [A01.456]
6. [F] …… Neck [A01.598]
7. [G] ….
8. Physical Sciences [H]
9. [I]
10. [J]
11. [K]
12. [L]
13. [M]

14. Descending the Hierarchy
1. Anatomy [A] Body Regions [A01] Abdomen [A01.047]
2. [B] Musculoskeletal System [A02] Back [A01.176]
3. [C] Digestive System [A03] Breast [A01.236]
4. [D] Respiratory System [A04] Extremities [A01.378]
5. [E] Urogenital System [A05] Head [A01.456]
6. [F] …… Neck [A01.598]
7. [G] ….
8. Physical Sciences [H] Electronics
9. [I] Astronomy
10. [J] Nature
11. [K] Time
12. [L] Weights and Measures
13. [M] ….

15. Descending the Hierarchy
1. Anatomy [A] Body Regions [A01] Abdomen [A01.047]
2. [B] Musculoskeletal System [A02] Back [A01.176]
3. [C] Digestive System [A03] Breast [A01.236]
4. [D] Respiratory System [A04] Extremities [A01.378]
5. [E] Urogenital System [A05] Head [A01.456]
6. [F] …… Neck [A01.598]
7. [G] ….
8. Physical Sciences [H] Electronics Amplifiers
9. [I] Astronomy Electronics, Medical
10. [J] Nature Transducers
11. [K] Time
12. [L] Weights and Measures
13. [M] ….

16. Descending the Hierarchy
1. Anatomy [A] Body Regions [A01] Abdomen [A01.047]
2. [B] Musculoskeletal System [A02] Back [A01.176]
3. [C] Digestive System [A03] Breast [A01.236]
4. [D] Respiratory System [A04] Extremities [A01.378]
5. [E] Urogenital System [A05] Head [A01.456]
6. [F] …… Neck [A01.598]
7. [G] ….
8. Physical Sciences [H] Electronics Amplifiers
9. [I] Astronomy Electronics, Medical
10. [J] Nature Transducers
11. [K] Time
12. [L] Weights and Measures Calibration
13. [M] … Metric System
Reference Standard

17. Descending the Hierarchy
1. Anatomy [A] Body Regions [A01] Abdomen [A01.047]
2. [B] Musculoskeletal System [A02] Back [A01.176]
3. [C] Digestive System [A03] Breast [A01.236]
4. [D] Respiratory System [A04] Extremities [A01.378]
5. [E] Urogenital System [A05] Head [A01.456]
6. [F] …… Neck [A01.598]
7. [G] ….
8. Physical Sciences [H] Electronics Amplifiers
9. [I] Astronomy Electronics, Medical
10. [J] Nature Transducers
11. [K] Time
12. [L] Weights and Measures Calibration
13. [M] … Metric System
Reference Standard
Homogeneous
Heterogeneous

18. Mapping Nouns to MeSH Concepts
headache recurrence
C C
headache pain
C G
breast cancer cells
A C A11

19. Levels of Description headache pain Level 0: C.23 G.11…
Original: C G

20. Outline Related work Linguistic motivation Lexical Hierarchy: MeSH
Labeling NC relations
Method and results
Discussion of ambiguity

21. Descent of Hierarchy Idea: Hypothesis:
Words falling in homogeneous MeSH subhierarchies behave “similarly” with respect to relation assignment
Hypothesis:
A particular semantic relation holds between all 2-word NCs that can be categorized by a MeSH category pairs

22. Grouping the NCs CP: A02 C04 (Musculoskeletal System, Neoplasms)
skull tumors, bone cysts, bone metastases, skull osteosarcoma…
CP: C04 M01 (Neoplasms, Person)
leukemia survivor, lymphoma patients, cancer physician, cancer nurses…

23. Distribution of Category Pairs

24. Collection ~70,000 NCs extracted from titles and abstracts of Medline
2,627 CPs at level 0 (with at least 10 unique NCs)
We analyzed
250 CPs with Anatomy (A)
21 CPs with Natural Science (H01)
3 CPs with Neoplasm (C04)
This represents 10% of total CPs and 20% of total NCs

25. Classification Method
For each CP
Divide its NCs into “training-testing” sets
“Training”: inspect NCs by hand
Start from level 0 0
While NCs are not all similar
descend one level of the hierarchy
Repeat until all NCs for that CP are similar

26. Using the CPs for classification
CP: A02 C04 (Musculoskeletal System, Neoplasms)
skull tumors, bone cysts, bone metastases, skull osteosarcoma

27. Using the CPs for classification
CP: A02 C04 (Musculoskeletal System, Neoplasms)
skull tumors, bone cysts, bone metastases, skull osteosarcoma
Similar NCs
All NCs under the CP A02 C04 have the same semantic relationship
Location of disease? Disease in Anatomy?

28. Using the CPs for classification
CP: A02 C04 (Musculoskeletal System, Neoplasms)
skull tumors, bone cysts, bone metastases, skull osteosarcoma
Similar NCs
All NCs under the CP A02 C04 have the same semantic relationship
Location of disease? Disease in Anatomy?
Add CP: A02 C04 to the list of classification decisions
Classification decisions
A02 C04

29. Using the CPs for classification
CP: B06 B06 (Plants, Plants)
eucalyptus trees, apple fruits, rice grains, potato plants
Classification decisions
A02 C04

30. Using the CPs for classification
CP: B06 B06 (Plants, Plants)
eucalyptus trees, apple fruits, rice grains, potato plants
Similar
Same relationship
Add CP B06 B06
Classification decisions
A02 C04
B06 B06

31. Using the CPs for classification
CP: C04 M01 (Neoplasms, Person)
leukemia survivor, lymphoma patients, cancer physician, cancer nurses…
Person afflicted by Disease? Person who treat Disease?
Too different!
Second noun needs to be more specific: Descend one level for the second noun Person
Classification decisions
A02 C04
B06 B06

32. Using the CPs for classification
CP: C04 M01 (Neoplasm, Person)
leukemia survivor, lymphoma patients, cancer physician, cancer nurses…
 Too different!
CP: C04 M (Neoplasms, Patients)
leukemia survivor, lymphoma patients
Person afflicted by Disease
CP: C04 M (Neoplasms, Occupational Groups)
cancer physician, cancer nurses…
Person who treat Disease OK
Classification decisions
A02 C04
B06 B06
C04 M01 
C04 M01.643
C04 M01.526

33. Classification Decisions
A02 C04
B06 B06
C04 M01
C04 M01.643
C04 M01.526
A01 H01
A01 H01.770
A01 H01.671
A01 H
A01 H
A01 M01
A01 M01.643
A01 M01.526
A01 M01.898

34. Classification Decisions + Relations (future work)
A02 C04  Location of Disease
B06 B06  Kind of Plants
C04 M01
C04 M  Person afflicted by Disease
C04 M  Person who treats Disease
A01 H01
A01 H01.770
A01 H01.671
A01 H
A01 H
A01 M01
A01 M01.643
A01 M01.526
A01 M01.898

35. Classification Decisions + Relations (future work)
A02 C04  Location of Disease
B06 B06  Kind of Plants
C04 M01
C04 M  Person afflicted by Disease
C04 M  Person who treats Disease
A01 H01
A01 H01.770
A01 H01.671
A01 H
A01 H
A01 M01
A01 M  Person afflicted by Disease
A01 M01.526
A01 M01.898

36. Classification Decision Levels
Anatomy: 250 CPs
187 (75%) remain first level
56 (22%) descend one level
7 (3%) descend two levels
Natural Science (H01): 21 CPs
1 (4%) remain first level
8 (39%) descend one level
12 (57%) descend two levels
Neoplasms (C04) 3 CPs:
3 (100%) descend one level

37. Evaluation Test the decisions on “testing” set
Count how many NCs that fall in the groups defined in the classification decisions are similar to each other
Accuracy:
Anatomy: 91% accurate
Natural Science: 79%
Neoplasm: 100%
Total Accuracy : 90.8%
Generalization: our 415 classification decisions cover ~ 46,000 possible CP pairs

38. Outline Related work Linguistic motivation Lexical Hierarchy: MeSH
Labeling NC relations
Method and results
Discussion of ambiguity

39. Ambiguity – Two Types Lexical ambiguity: Relationship ambiguity:
mortality
state of being mortal
death rate
Relationship ambiguity:
bacteria mortality
death of bacteria
death caused by bacteria

40. Lexical Ambiguity vs. Multiple MeSH Senses
Lexical ambiguity different from multiple MeSH senses
Ex: Mortality has 4 senses
Public Health (G)  Data Collection  Vital Statistics   Mortality
Investigative Techniques (E)  Data Collection  Vital Statistics   Mortality
Information Science (L)  Data Collection  Vital Statistics   Mortality
Population Characteristics (N)  Demography  Vital Statistics   Mortality
On average, there are 1.5 MeSH senses per word for the nouns in our collection

41. Four Cases Single MeSH senses Multiple MeSH senses Ambiguity of
Only one possible relationship: abdomen radiography, aciclovir treatment
Only one possible relationship: alcoholism treatment
Multiple relationships: hospital databases, education efforts, kidney metabolism
Multiple relationships bacteria mortality
Ambiguity of
relationship

42. Four Cases Single MeSH senses Multiple MeSH senses
Only one possible relationship: abdomen radiography, aciclovir treatment
Only one possible relationship: alcoholism treatment
Multiple relationships: hospital databases, education efforts, kidney metabolism
Multiple relationships bacteria mortality
Most problematic cases
Ambiguity of
relationship
… but rare!

43. Conclusions
Very simple method for assigning semantic relations to two-word technical NCs
90.8% accuracy
Grouping the NCs with respect to their semantic descriptors
Lexical resource (MeSH) useful for this task
Use the upper levels of the lexical hierarchy for an accurate classification, reducing therefore the space of the problem

44. Future work Analyze full spectrum of hierarchy NCs with > 2 terms
[[growth hormone] deficiency]
Other syntactic structures
Non-biomedical words
Other ontologies (e.g.,WordNet)?

45. And given enough data… skull character jaw depression
nose resuscitation
cadaver motion

46. Thanks! For more information: http://bailando.sims.berkeley.edu/lindi/