Clustering Semantically Similar Words

Clustering SemanticallySimilar Words

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DSW Camp & JamDecember 4th, 2016

Bayu Aldi Yansyah

- Understand step-by-step how to cluster words based on their

semantic similarity

- Understand how Deep learning model is applied to Natural

Language Processing

Our GoalsOverview

- You understand the basic of Natural Language Processing and

Machine Learning

- You are familiar with Artificial neural networks

I assume …Overview

1. Introduction to Word Clustering

2. Introduction to Word Embedding

- Feed-forward Neural Net Language Model

- Continuous Bag-of-Words Model

- Continuous Skip-gram Model

3. Similarity metrics

- Cosine similarity

- Euclidean similarity

4. Clustering algorithm: Consensus clustering

OutlineOverview

1.WORD CLUSTERINGINTRODUCTION

- Word clustering is a technique for partitioning sets of words into

subsets of semantically similar words

- Suppose we have set of words W = w$,w&,… ,w( , n ∈ ℕ , our goal is

to find C = C$,C&,…, C. , k ∈ ℕ where

- w1 is a centroid of cluster C2- similarity w1,w is a function to measure the similarity score

- and 𝑡 is a threshold value where if 𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑦 𝑤D ,𝑤 ≥ 𝑡means that

𝑤D and 𝑤is semantically similar.

- For 𝑤$ ∈ 𝐶G and 𝑤& ∈ 𝐶H apply that 𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑦 𝑤$,𝑤& < 𝑡, so

𝐶J = 𝑤 ∀𝑤 ∈𝑊where𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑦 𝑤D, 𝑤 ≥ 𝑡}

𝐶G ∩𝐶H = ∅, ∀𝐶G,𝐶H ∈ 𝐶

1.WORD CLUSTERINGINTRODUCTION

In order to perform word clustering, we need to:

1. Represent word as vector semantics, so we can compute their

similarity and dissimilarity score.

2. Find the w1 for each cluster.

3. Choose the similarity metric 𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑦 𝑤D,𝑤 and the threshold

value 𝑡.

Semantic ≠ Synonym

“Words are similar semantically if they have the same thing, are

opposite of each other, used in the same way, used in the same

context and one is a type of another.” − Gomaa and Fahmy (2013)

2.WORD EMBEDDINGINTRODUCTION

- Word embedding is a technique to represent a word as a vector.

- The result of word embedding frequently referred as “word vector”

or “distributed representation of words”.

- There are 3 main approaches to word embedding:

1. Neural Networks model based

2. Dimensionality reduction based

3. Probabilistic model based

- We focus on (1)

- The idea of these approaches are to learn vector representations of

words in an unsupervised manner.

2.WORD EMBEDDINGINTRODUCTION

- Some Neural networks models that can learn representation of

words are:

1. Feed-forward Neural Net Language Model by

Bengio et al. (2003).

2. Continuous Bag-of-Words Model by Mikolov et al. (2013).

3. Continuous Skip-gram Model by Mikolov et al. (2013).

- We will compare these 3 models.

- Fun fact: the last two models is highly-inpired by no 1.

- Only Feed-forward Neural Net Language Model is considered as

deep learning model.

2.WORD EMBEDDINGCOMPARING NEURAL NETWORKS MODELS

- We will use notation from Collobert et al. (2011) to represent the

model. This help us to easily compare the models.

- Any feed-forward neural network with 𝐿 layers can be seen as a

composition of functions 𝑓TU(W), corresponding to each layer 𝑙:

- With parameter for each layer 𝑙:

- Usually each layer 𝑙 have weight 𝑊and bias 𝑏, 𝜃U = (𝑊U ,𝑏U).

𝑓T W = 𝑓T[(𝑓T[\$(… 𝑓T$(W)… ))

𝜃 = (𝜃$,𝜃&, …, 𝜃[)

2.1.FEED-FORWARD NEURAL NET LANGUAGE MODELBengio et al. (2003)

- The training data is a sequence of words 𝑤$,𝑤& ,… ,𝑤] for 𝑤^ ∈ 𝑉

- The model is trying predict the next word 𝑤^ based on the previous

context (previous 𝑛 words: 𝑤^\$,𝑤^\&,… ,𝑤^\a). (Figure 2.1.1)

- The model is consist of 4 layers: Input layer, Projection layer, Hidden

layer(s) and output layer. (Figure 2.1.2)

- Known as NNLM

𝑤^

Keren Sale Stock bisa dirumah... ...

𝑤^\$𝑤^\&𝑤^\b𝑤^\c

Figure 2.1.1

2.1.FEED-FORWARD NEURAL NET LANGUAGE MODELCOMPOSITION OF FUNCTIONS: INPUT LAYER

- 𝑥^\$,𝑥^\&,… , 𝑥^\a is a 1-of-|𝑉| vector or one-hot-encoded vector of

𝑤^\$,𝑤^\&,… ,𝑤^\a- 𝑛 is the number of previous words

- The input layer is just acting like placeholder here

𝑥′^ = 𝑓T 𝑥^\$,… , 𝑥^\a

Output layer : 𝑓Tc J= 𝑥′^ = 𝜎 𝑊c] 𝑓Tb J +𝑏

c

Hidden layer : 𝑓Tb J= tanh 𝑊b] 𝑓T& J +𝑏

b

Projection layer : 𝑓T& J = 𝑊&] 𝑓T$ J

Input layer for i-th example : 𝑓T$ J = 𝑥^\$, 𝑥^\&,… , 𝑥^\a

2.1.FEED-FORWARD NEURAL NET LANGUAGE MODELCOMPOSITION OF FUNCTIONS: PROJECTION LAYER

- The idea of this layer is to project the |𝑉|-dimension vector to

smaller dimension.

- 𝑊& is the |𝑉|×𝑚 matrix, also known as embedding matrix, where

each row is a word vector

- Unlike hidden layer, there is no non-linearity here

- This layer also known as “The shared word features layer”

𝑥′^ = 𝑓T 𝑥^\$,… , 𝑥^\a


c


b



2.1.FEED-FORWARD NEURAL NET LANGUAGE MODELCOMPOSITION OF FUNCTIONS: HIDDEN LAYER

- 𝑊b is the ℎ×𝑛𝑚 matrix where ℎ is the number of hidden units.

- 𝑏b is a ℎ −dimensional vector.

- The activation function is hyperbolic tangent.

𝑥′^ = 𝑓T 𝑥^\$,… , 𝑥^\a


c


b



2.1.FEED-FORWARD NEURAL NET LANGUAGE MODELCOMPOSITION OF FUNCTIONS: OUPTUT LAYER

- 𝑊c is the ℎ×|𝑉| matrix.

- 𝑏c is a |𝑉|-dimensional vector.

- The activation function is softmax.

- 𝑥′^ is a |𝑉|-dimensional vector.

𝑥′^ = 𝑓T 𝑥^\$,… , 𝑥^\a


c


b



2.1.FEED-FORWARD NEURAL NET LANGUAGE MODELLOSS FUNCTION

- Where 𝑁 is the number of training data

- The goal is to maximize this loss function.

- The neural networks are trained using stochastic gradient ascent.

𝐿 =1𝑁nlog 𝑓T 𝑥^\$,…, 𝑥^\a; 𝜃 J

r

Js$

Figure 2.1.2 Flow of the tensor of Feed-forward Neural Net Language Model

with vocabulary size |𝑉| and hyperparameter 𝑛 = 4,𝑚 = 2

and ℎ = 5.

𝑥^\$𝑥^\&𝑥^\b𝑥^\c

𝑣^\$𝑣^\&𝑣^\b𝑣^\c

𝑥′^

2.2.CONTINUOUS BAG-OF-WORDS MODELMikolov et al. (2013)


- The model is trying predict the word 𝑤^ based on the surrounding

context (𝑛words from left: 𝑤^\$,𝑤^\& and 𝑛 words from the right:

𝑤^\$,𝑤^\&). (Figure 2.2.1)

- There are no hidden layer in this model.

- Projection layer is averaged across input words.

𝑤^x&

Keren Sale bisa bayar dirumah... ...

𝑤^x$𝑤^𝑤^\$𝑤^\&

Figure 2.2.1

2.2.CONTINUOUS BAG-OF-WORDS MODELCOMPOSITION OF FUNCTIONS: INPUT LAYER

- 𝑥^\y is a 1-of-|𝑉| vector or one-hot-encoded vector of 𝑤^\y .

- 𝑛 is the number of words on the left and the right.

𝑥′^ = 𝑓T 𝑥^\a,… , 𝑥^\$,𝑥^x$,…, 𝑥^xa

Output layer : 𝑓Tb J= 𝑥′^ = 𝜎 𝑊b] 𝑓T& J +𝑏

b

Projection layer : 𝑓T& J = 𝑣 =12𝑛

n 𝑊&] 𝑓T$(𝑗) J

\a{y{a,y|}

y

Input layer for i-th example : 𝑓T$(𝑗) J = 𝑥^\y ,−𝑛 ≤ 𝑗 ≤ 𝑛, 𝑗 ≠ 0

2.2.CONTINUOUS BAG-OF-WORDS MODELCOMPOSITION OF FUNCTIONS: PROJECTION LAYER

- The difference from previous model is this model project all the

inputs to one 𝑚-dimensional vector 𝑣.


each row is a word vector.

𝑥′^ = 𝑓T 𝑥^\a,… , 𝑥^\$,𝑥^x$,…, 𝑥^xa


b



\a{y{a,y|}

y


2.2.CONTINUOUS BAG-OF-WORDS MODELCOMPOSITION OF FUNCTIONS: OUPTUT LAYER

- 𝑊b is the m×|𝑉| matrix.

- 𝑏b is a |𝑉|-dimensional vector.


- 𝑥′^ is a |𝑉|-dimensional vector.

𝑥′^ = 𝑓T 𝑥^\a,… , 𝑥^\$,𝑥^x$,…, 𝑥^xa


b



\a{y{a,y|}

y


2.2.CONTINOUS BAG-OF-WORDS MODELLOSS FUNCTION




𝐿 =1𝑁nlog 𝑓T 𝑥^\a ,… , 𝑥^\$, 𝑥^x$,… , 𝑥^xa J

r

Js$

𝑥^x&𝑥^x$𝑥^\$𝑥^\&

𝑥′^

𝑣

Figure 2.2.2 Flow of the tensor of Continuous Bag-of-Words Model with

vocabulary size |𝑉| and hyperparameter 𝑛 = 2,𝑚 = 2.

2.3.CONTINUOUS SKIP-GRAM MODELMikolov et al. (2013)


- The model is trying predict the surrounding context (𝑛words from

left: 𝑤^\$,𝑤^\& and 𝑛 words from the right: 𝑤^\$,𝑤^\&) based on the

word 𝑤^ . (Figure 2.3.1)

𝑤^x&

Keren bisa... ...

𝑤^x$𝑤^𝑤^\$𝑤^\&

Figure 2.3.1

2.3.CONTINUOUS SKIP-GRAM MODELCOMPOSITION OF FUNCTIONS: INPUT LAYER

- 𝑥^ is a 1-of-|𝑉| vector or one-hot-encoded vector of 𝑤^ .

𝑋′ = 𝑓T 𝑥^

Output layer : 𝑓Tb J= 𝑋′ = 𝜎 𝑊b] 𝑓T& J +𝑏

b


Input layer for i-th example : 𝑓T$ J = 𝑥^

2.3.CONTINUOUS SKIP-GRAM MODELCOMPOSITION OF FUNCTIONS: PROJECTION LAYER


each row is a word vector.

- Same as Continuous Bag-of-Words model



b



2.3.CONTINUOUS SKIP-GRAM MODELCOMPOSITION OF FUNCTIONS: OUTPUT LAYER

- 𝑊b is the m×2𝑛|𝑉| matrix.

- 𝑏b is a 2n|𝑉|-dimensional vector.


- 𝑋� is a 2n|𝑉|-dimensional vector can be written as



b



𝑋� = (𝑝(𝑤^\a|𝑤^),… , 𝑝(𝑤^\$|𝑤^), 𝑝(𝑤^x$|𝑤^ ),… , 𝑝(𝑤^xa|𝑤^))

2.3.CONTINOUS SKIP-GRAM MODELLOSS FUNCTION




𝐿 =1𝑁nlog n 𝑝(𝑤^\y|𝑤^ )

\a{y{a,y|}

y J

r

Js$

𝑥^x&𝑥^x$𝑥^\$𝑥^\&

𝑥^

𝑣

Figure 2.3.2 The flow of tensor of Continuous Skip-gram Model with

vocabulary size |𝑉| and hyperparameter 𝑛 = 2,𝑚 = 2.

3.SIMILARITY METRICSINTRODUCTION

- Recall 𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑦 𝑤D ,𝑤 ≥ 𝑡

- Similarity metrics of words: Character-Based Similarity Measures

and Term-based Similarity Measures. (Gomaa and Fahmy 2013)

- We focus on Term-based Similarity Measures

3.SIMILARITY METRICSINTRODUCTION

- Recall 𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑦 𝑤D ,𝑤 ≥ 𝑡

- Similarity metrics of words: Character-Based Similarity Measures

and Term-based Similarity Measures. (Gomaa and Fahmy 2013)

- We focus on Term-based Similarity Measures: Cosine & Euclidean.

3.1.SIMILARITY METRICSCOSINE

- Where 𝑣J is our word vector

- Range value: −1 ≤ 𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑦 𝑣$,𝑣& ≤ 1

- Recommended threshold value : 𝑡 ≥ 0.5

𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑦 𝑣$, 𝑣& = 𝑣$ W 𝑣&𝑣$ 𝑣&

3.2.SIMILARITY METRICSEUCLIDEAN

- Where 𝑣J is our word vector

- Range value: 0 ≤ 𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑦 𝑣$, 𝑣& ≤ 1

- Recommended threshold value : 𝑡 ≥ 0.75

𝑠𝑖𝑚𝑖𝑙𝑎𝑟𝑖𝑡𝑦 𝑣$,𝑣& =1

1 −𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (𝑣$,𝑣&)

𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑣$,𝑣& = n(𝑣$J − 𝑣&J)&a

Js$

4.CONSENSUS CLUSTERINGINTRODUCTION

- The basic idea here is we want to find the 𝑤D based on the

consensus

- There are 3 approaches for Consensus clustering: Iterative Voting

Consensus, Iterative Probabilistic Voting Consensus and Iterative

Pairwise Consensus. (Nguyen and Caruana 2007)

- We use slightly modified version of Iterative Voting Consensus

4.1.CONSENSUS CLUSTERINGTHE ALGORITHM

Figure 4.1.1 Iterative Voting Consensus with slightly modification

5.CASE STUDYOR DEMO

- Let’s do this

thanks! | @bayualsyah

Notes available here: https://github.com/pyk/talks

Clustering Semantically Similar Words

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