Incorporating Latent Meanings of Morphological Compositions to Enhance Word Embeddings. Yang Xu, Jiawei Liu, Wei Yang, and Liusheng Huang

Transcription

1 Incorporating Latent Meanings of Morphological Compositions to Enhance Word Embeddings Yang Xu, Jiawei Liu, Wei Yang, and Liusheng Huang School of Computer Science and Technology, University of Science and Technology of China, Hefei, , China July 17 th 2018

2 01 Introduction OUTLINE 02 Latent Meaning Models 03 Experimental Setup 04 Experimental Results 05 Conclusion!2

3 01 Introduction 3

4 Word-level Word Embedding 01 Neural Network-Based e.g., GloVe (Pennington et al.) INPUT PROJECTION OUTPUT w(t-2) INPUT PROJECTION OUTPUT w(t-2) w(t-1) SUM w(t) w(t) SUM w(t-1) word-word co-occurrence matrix w(t+1) w(t+1) w(t+2) w(t+2) CBOW Skip-gram e.g., CBOW, Skip-gram (Mikolov et al.) 02 Matrix Factorization-Based ( Spectral Methods ) 4

5 Morphology-based Word Embedding Morpheme Embeddings 01 Prefix Root Suffix in cred ible Word Embeddings Word incredible Training Model Generated Word Vectors Generated Word Generative Model Morpheme Embeddings Prefix Root Suffix!5 02

6 Our Original Intention Word-level models: InputWords; Output Word Embeddings Morphology-based models: Input Words + Morphemes Output Word Embeddings + Morpheme Embeddings Our Latent Meaning Models: InputWords + Latent Meanings of Morphemes Output Word Embeddings ( no by-product, e.g., morpheme embedding) PURPOSE: to not only encode morphological properties into words, but also enhance the semantic similarities among word embeddings!6

7 Explicit Models & Our Models Corpus sentence i : Explicit models directly use morphemes in cred ible it is an incredible in not believe able thing capable Lookup table Prefix Latent Meaning in un in, not not Root Latent Meaning sentence j : un believ able it is unbelievable that not believe able capable believ cred believe believe Suffix Latent Meaning Our models employ the latent meanings of morphemes *Note: The lookup table can be derived from morphological lexicons.!7 able ible able, capale able, capale

8 02 Latent Meaning Models!8

9 CBOW with Negative Sampling Sequence of tokens INPUT PROJECTION OUTPUT t i-2 Objective Function: L = 1 n n i=1 logp(t i Context(t i )) t i-1 SUM t i t i+1 (Target Word) Negative Sampling: t i+2 (Context Words)!9

10 Three Specific Models LMM-A (Latent Meaning Model-Average) 02 LMM-M (Latent Meaning Model-Max) LMM-S (Latent Meaning Model-Similarity)!10

11 Word Map incredible Lookup table Prefix Latent Meaning Word Map in cred ible in un in, not not Word Prefix Root Suffix unbelievable un believ able Root Latent Meaning believ cred believe believe Suffix Latent Meaning able ible able, capale able, capale incredible in not believe able capable unbelievable not believe able capable #rows = vocabulary *Note: The derivational morphemes, not the inflectional morphemes, are mainly concerned!11

12 Latent Meaning Model-Average (LMM-A) Sequence of tokens The latent meanings of s morphemes have equal contributions to A paradigm of LMM-A The modified embedding of : Latent Meaning in Prefix not Root believe 1/ 5 1/ 5 1/ 5 Context(t i) it is SUM t i an : a set of latent meanings of s morphemes : the length of Suffix capable able 1/ 5 1/ 5 incredible thing is utilized for training An item of the Word Map Word Prefix Root Suffix incredible in not believe able capable!12

13 Latent Meaning Model-Similarity (LMM-S) Sequence of tokens The latent meanings of s morphemes are assigned with different weights: ω <tj, w> = cos ( v tj, v w ) x Mj cos ( v tj, v x ) The modified embedding of :, w M j : a set of latent meanings of s morphemes Latent Meaning Prefix Root Suffix in not believe capable able it is incredible thing An item of the Word Map Word Prefix Root Suffix incredible A paradigm of LMM-S? in? not? believe? capable? able Context(t i) in not believe able capable SUM t i an!13

14 Latent Meaning Model-Max (LMM-M) Sequence of tokens Keep the latent meanings that have maximum similarities to : Pmax j = argmax cos w ( v tj, v w ), w P j cos ( v tj, v w ), w R j R j max = argmax w S j max = argmax w cos ( v tj, v w ), w S j The modified embedding of : M j max = {P j max, Rj max, Sj max} Latent Meaning Prefix Root Suffix in not believe capable able it is incredible thing An item of the Word Map Word Prefix Root Suffix incredible A paradigm of LMM-M? not? believe? able Context(t i) in not believe able capable SUM t i an!14

15 Update Rules for LMMs New Objective Function (After modifying the input layer of CBOW): ^ L = 1 n n i=1 logp(v ti ^v tj ) t j Context(t i) All parameters introduced by our models can be directly derived using the word map and word embeddings Update not just but the embeddings of the latent meanings with the same weights as they are assigned in the forward propagation period!15

16 03 Experimental Setup!16

17 Corpus & Word Map Corpus Word Map News corpus of 2009 (2013 ACL Eighth Workshop) Size: 1.7GB ~500 million tokens ~600,000 words Digits & punctuation marks are filtered Morpheme segmentation using Morefessor (Creutz & Lagus, 2007) Assign latent meanings Lookup table derived from the resources provided by Michigan State University* 90 prefixes, 382 roots, 67 suffixes *Resources web link:

18 Baselines & Parameter Settings Baselines:! Word-level models: CBOW, Skip-gram, GloVe! Explicitly Morpheme-related Model (EMM) A paradigm of EMM Morphemes it Super-parameter Settings:! Equal settings to all models! Vector Dimension: 200 Prefix Root in cred is incredible SUM an! Context window size: 5 Suffix ible thing! #Negative_Samples: 20!18

19 Evaluation Benchmarks (1/2) Word Similarity: Dataset Name #Pairs Name #Pairs Name #Pairs RG Rare-Word 2034 Men-3k 3000 Wordsim SCWS 2003 WS-353-Related 252 Gold Standard Datasets Widely-used Datasets Syntactic Analogy:! a b as c? (d) e.g., Queen King as Woman (Man)! Microsoft Research Syntactic Analogies dataset (8000 items)!19

20 Evaluation Benchmarks (2/2) Text Classification:! 20 Newsgroups dataset (19000 documents of 20 different topics)! 4 text classification tasks, each involves 10 topics! Training/Validation/Test subsets (6:2:2)! Feature vector: average word embedding of words in each document! L2-regularized logistic regression classifier!20

21 04 Experimental Results!21

22 The Results on Word Similarity CBOW Skip-gram GloVe EMM LMM-A LMM-S LMM-M Wordsim Rare-Word RG SCWS Men-3k WS-353-Related (Given different models) Spearman s rank correlation (%) on different datasets!22

23 The Results on Syntactic Analogy Question: a b as c (d) Answer: CBOW Skip-gram GloVe EMM LMM-A LMM-S LMM-M Syntactic Analogy Syntactic analogy performance (%)!23

24 The Results on Text Classification CBOW Skip-gram GloVe EMM LMM-A LMM-S LMM-M Text Classification Average text classification accuracy across the 4 tasks (%)!24

25 The Impact of Corpus Size Results on Wordsim-353 task with different corpus size!25

26 The Impact of Context Window Size Results on Wordsim-353 task with different context window size!26

27 Word Embedding Visualization latent meanings of morphemes Visualization of word embeddings based on PCA!27

28 05 Conclusions!28

29 Conclusions Employ latent meanings of morphemes rather than the internal compositions themselves to train word embeddings By modifying the input layer and update rules of CBOW, we proposed three latent meaning models (LMM-A, LMM-S, LMM-M) The comprehensive quality of word embedings are enhanced by incorporating latent meanings of morphemes In the future, we intend to evaluate our models for some morpheme-rich languages like Russian, German, etc.!29

30 Thank you! Questions?