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

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

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

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.

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

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. 13 classes, 52% accuracy Probabilistic Lauer (1995): probabilistic model, 8 classes, 47% accuracy Lapata (2000) classifies nominalizations into subject/object. 2 classes, 80% accuracy

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

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…

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

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

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]

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]

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]

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] ….

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] ….

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

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

Mapping Nouns to MeSH Concepts headache recurrence C23.888.592.612.441 C23.550.291.937 headache pain C23.888.592.612.441 G11.561.796.444 breast cancer cells A01.236 C04 A11

Levels of Description headache pain Level 0: C.23 G.11 … Original: C23.888.592.612.441 G11.561.796.444

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

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

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…

Distribution of Category Pairs

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

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

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

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?

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

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

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

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

Using the CPs for classification CP: C04 M01 (Neoplasm, Person) leukemia survivor, lymphoma patients, cancer physician, cancer nurses…  Too different! CP: C04 M01.643 (Neoplasms, Patients) leukemia survivor, lymphoma patients Person afflicted by Disease CP: C04 M01.526 (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

Classification Decisions A02 C04 B06 B06 C04 M01 C04 M01.643 C04 M01.526 A01 H01 A01 H01.770 A01 H01.671 A01 H01.671.538 A01 H01.671.868 A01 M01 A01 M01.643 A01 M01.526 A01 M01.898

Classification Decisions + Relations (future work) A02 C04  Location of Disease B06 B06  Kind of Plants C04 M01 C04 M01.643  Person afflicted by Disease C04 M01.526  Person who treats Disease A01 H01 A01 H01.770 A01 H01.671 A01 H01.671.538 A01 H01.671.868 A01 M01 A01 M01.643 A01 M01.526 A01 M01.898

Classification Decisions + Relations (future work) A02 C04  Location of Disease B06 B06  Kind of Plants C04 M01 C04 M01.643  Person afflicted by Disease C04 M01.526  Person who treats Disease A01 H01 A01 H01.770 A01 H01.671 A01 H01.671.538 A01 H01.671.868 A01 M01 A01 M01.643  Person afflicted by Disease A01 M01.526 A01 M01.898

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

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

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

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

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

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

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!

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

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)?

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

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