CLASSIFYING ENTITIES INTO AN INCOMPLETE ONTOLOGY Bhavana Dalvi, William W. Cohen, Jamie Callan School of Computer Science, Carnegie Mellon University
Motivation Existing Techniques Semi-supervised Hierarchical Classification: Carlson WSDM’10 Extending knowledge bases: Finding new relations or attributes of existing concepts Mohamed et al. EMNLP’11 Unsupervised ontology discovery: Adams et al. NIPS’10, Blei et al. JACM’10, Reisinger et al. ACL’09 Evolving Web-scale datasets Billions of entities and hundreds of thousands of concepts Difficult to create a complete ontology Hierarchical classification of entities into incomplete ontologies is needed
Contributions Hierarchical Exploratory EM Adds new instances to the existing classes Discovers new classes and adds them at appropriate places in the ontology Class constraints: Inclusion: Every entity that is “Mammal” is also an “Animal” Mutual Exclusion: If an entity is “Electronic Device” then its not “Mammal”
Problem Definition
Review: Exploratory EM [Dalvi et al. ECML 2013] Initialize model with few seeds per class Iterate till convergence (Data likelihood and # classes) E step: Predict labels for unlabeled points If P(Cj | Xi) is nearly-uniform for a data-point Xi, j=1 to k Create a new class C k+1, assign Xi to it M step: Recompute model parameters using seeds + predicted labels for unlabeled points Number of classes might increase in each iteration Check if model selection criterion is satisfied If not, revert to model in Iteration `t-1’ Classification/clustering KMeans, NBayes, VMF … Max/Min ratio JS Divergence AIC, BIC, AICc …
Hierarchical Exploratory EM
Divide-And-Conquer Exploratory EM Mutual ExcIusion Root Food Location Country State Vegetable Condiment Inclusion E.g. Spinach, Potato, Pepper… Level 1 Level 2 Level 3 Assumptions: Classes are arranged in a tree- structured hierarchy. Classes at any level of the hierarchy are mutually exclusive.
Divide-And-Conquer Exploratory EM Root Food Location Country State Vegetable Condiment 1.0 California
Divide-And-Conquer Exploratory EM Root Food Location Country State Vegetable Condiment 1.0 California
Divide-And-Conquer Exploratory EM Root Food Location Country State Vegetable Condiment 1.0 California
Divide-And-Conquer Exploratory EM Root Food Location Country State Vegetable Condiment 1.0 Coke
Divide-And-Conquer Exploratory EM Root Food Location Country State Vegetable Condiment 1.0 Coke
Divide-And-Conquer Exploratory EM Root Food Location Country State Vegetable Condiment 1.0 Coke
Divide-And-Conquer Exploratory EM Root Food Location Country State Vegetable Condiment 1.0 Coke C8 Coke
Divide-And-Conquer Exploratory EM Root Food Location Country State Vegetable Condiment 1.0 Coke Coke
Divide-And-Conquer Exploratory EM Root Food Location Country State Vegetable Condiment 1.0 Cat C8 C Cat
What are we trying to optimize? Objective Function : Maximize { Log Data Likelihood – Model Penalty } m: #clusters, Params{C1… Cm} subject to Class constraints: Z m
Datasets Ontology 1 Ontology 2 Dataset#Classes#Levels#NELL entities #Contexts DS K3.4M DS K6.7M Clueweb09 Corpus + Subsets of NELL
Results Dataset#Train /Test Points DS-1335/ 2.2K DS-21.5K/ 11.4K
Results Dataset#Train /Test Points Level#Seed/ #Ideal Classes DS-1335/ 2.2K 22/3 34/7 DS-21.5K/ 11.4K 23.9/4 39.4/ /10
Results Dataset#Train /Test Points Level#Seed/ #Ideal Classes Macro-averaged Seed Class F1 FLAT SemisupEMExploratoryEM DS-1335/ 2.2K 22/ * 34/ * DS-21.5K/ 11.4K 23.9/ / * 42.4/ *
Results Dataset#Train /Test Points Level#Seed/ #Ideal Classes Macro-averaged Seed Class F1 FLATDAC SemisupEMExploratoryEMSemisupEMExploratoryEM DS-1335/ 2.2K 22/ * * 34/ * * DS-21.5K/ 11.4K 23.9/ * 39.4/ * * 42.4/ *
Conclusions
Thank You Questions?
Extra Slides
Class Creation Criterion
Model Selection Extended Akaike Information Criterion AICc(g) = -2*L(g) + 2*v + 2*v*(v+1)/(n – v -1) Here g: model being evaluated, L(g): log-likelihood of data given g, v: number of free parameters of the model, n: number of data-points.