A Panorama of Natural Language Processing

A Panorama ofNatural Language

Processing

Ted Xiao

Overview• Background

• Grammars

• Word Representation

• Modern NLP

• Future Directions

• NLP in Industry

• Demos

What is Natural Language Processing?

NLP!

Artificial Languages: Java, C++, Binary…


NLP!


Natural Language: Language spoken by people.


NLP!



Motivation: Sophisticated linguistic analysis for human-likesophistication for a range of tasks or applications.


NLP!

Goal: have computers understand natural language in order to perform useful tasks



Motivation: Sophisticated linguistic analysis for human-likesophistication for a range of tasks or applications.

Task Types● Syntax

○ Parsing○ Stemming○ Part of speech tagging

● Discourse○ Parsing○ Stemming○ Part of speech tagging

Task Types● Syntax

○ Parsing○ Stemming○ Part of speech tagging

● Semantics○ Machine Translation○ Natural Language

Understanding, Generation○ OCR○ QA, Sentiment Analysis○ Coreference

● Discourse○ Parsing○ Stemming○ Part of speech tagging

● Speech○ Speech Recognition○ Text-to-Speech○ Speech-to-Text

Task Examples

Task Examples

NLP in Industry

What Makes NLP Difficult?• We don’t understand language ourselves

• Language encodes meaning

• Language is learned intuitively - easy for children, hard for computers

or

What Makes NLP Difficult?• We don’t understand language ourselves

• Language encodes meaning

• Language is learned intuitively - easy for children, hard for computers

• Ambiguity

• Language is symbolic

• Subtleties: sarcasm, wordplay, idioms...

or

NLP vs. PLPProgramming Language Processing is easier than Natural Language Processing

● The Pope’s baby steps on gays

● Scientists study whales from space

● Juvenile court to try shooting defendant

● Boy paralyzed after tumor fights back to gain black belt

Examples of ambiguity: news headlines

An NLP Disaster

An NLP Disaster: Microsoft Tay (March 2016)

...again?! Microsoft Zo (December 2016)


• Linguistics


• Modern NLP


• NLP in Industry

• Demos

Grammars● Grammars are the formal description of the structure of a

language● Skeleton of any language

Basic Linguistics

Context

Form

Meaning

Structure

Audio

Levels of NLP


• Grammars


• Modern NLP


• NLP in Industry

• Demos

Digitalizing Natural Language

• Need to have some measure of similarity and differences between words• Vectors can do this!

Digitalizing Natural Language

• Need to have some measure of similarity and differences between words• Vectors can do this!• We can use vector operations to gauge similarity between words

Word Vectors• 13 million tokens in the English language

• Many words are similar (cat and feline, man and woman, etc…)

• A nice idea: encode word tokens into a vector that is a point in some

word space with dimension << 13 million

One-Hot Vectors

• Express each word as an |V| dimensional vector with one 1 and

the rest 0s, where |V| is the size of our vocabulary

• One-hot vectors for a dictionary would look like:

What’s Wrong?• One hot vectors are independent (orthogonal)

• But some words are similar!

• A nicer idea: reduce the size of the space from |V| to a smaller-

dimensional subspace that encodes relationships between words

Quick Aside: Singular Value Decomposition (SVD)

(mxm) matrix of left singular vectors

(nxn) matrix of right singular vectors

(mxn) matrix with the singular values of X on its diagonals

(mxn)

Take away point: The SVD of X is the best rank-k approximation

X = USVT

Illustration of the SVD as a Rank-k Approximation

SVD-Based Methods: Window-based Co-occurrence Matrix

• Only count the number of times a word appears inside a window of a particular size around the word of interest

• Consider the following three documents:• I enjoy flying• I like NLP• I like deep learning window size = 1

Applying the SVD to the co-occurrence matrix

• X = USVT

• Truncate S at some index k based on the amount of variance captured:

• Take the sub-matrix Ui:V,1:k to be our word embeddings

• Now have a k-dimensional representation of every word in our

vocabulary!

Downfalls of SVD-based Methods

• Co-occurrence matrix is high dimensional and sparse

• SVDs are computationally expensive (quadratic cost)

• Dimensions of the co-occurrence matrix are constantly

changing as new words are added

Downfalls of SVD-based Methods

• Co-occurrence matrix is high dimensional and sparse

• SVDs are computationally expensive (quadratic cost)

• Dimensions of the co-occurrence matrix are constantly

changing as new words are added

• Solution: iteration-based methods!

Iteration-based Methods

• Word Vectors and Word Embeddings: Used to Find similarity

Compute and store representative information about a huge dataset

• Iteration-based Methods: create a model that learns one iteration at a time that

will eventually be able to encode the probability of a word given its context

• These include basic language models as well as the more advanced word2vec

Basic Language Models

• Bag of Words

• Just count the frequencies of words.

• Issues: High dimension, and order and

relations are lost


• Bag of Words



relations are lost

• Term Frequency-inverse Document Frequency

• AKA TF-IDF

• How important a word is in a document

• Used in search engines!


• Question: Are there ways we can maintain

information about word order and meaning?

• Bag of Words



relations are lost

• Term Frequency-inverse Document Frequency

• AKA TF-IDF

• How important a word is in a document

• Used in search engines!

Language Models• Goal: assign a probability to a sequence of tokens

• Consider the two sentences:

• “The dog wagged his tail”

• “Puffer fish bank ladder”

• Which should have a higher probability?

• If we assume that word occurrences are independent, the

probability of any given sequence of words is:

(Unigram model)

What if Word Occurrences Are Not Independent?

• Assume the probability of a sequence depends on the pairwise

probability of a word in the sequence and a word next to it (bigrams)

• A bigram model is of the form:

• The general N-gram model is given by:

Approaches So Far● Simple models trained on huge amounts of data outperform complex

models trained on small amounts of data

● Unigrams:

● Bigrams:

● N-grams:

Continuous Bag of Words(CBOW)

• Consider part of the sequence of words as context, and try to predict the center words• Sentence: “The dog wagged his tail”• Context: {“The”, “dog”, “his”, “tail}• Center words: “wagged”

• Our known parameters are the sentence in question represented by one-hot vectors• Let x(c) denote the context words• Lets y(c) denote the target word (output)

Continuous Bag of Words

Skip-grams• Now, consider the center word as context and try to predict

surrounding words

• Sentence: “The dog wagged his tail”

• Context: “wagged”

• Surrounding words: {“The”, “dog”, “his”, “tail”}

• Nearly identical set-up to CBOW, except we switch our x and y

• Input: one-hot vector (context word)

• Output: vectors describing the surrounding words

Skip-grams

Recap● We first tried condensing language into word vectors

○ We want to keep meaning in a lower dimension

○ One-hot Vectors, SVD… These are expensive!




● We then tried iteration based methods

○ Language Models: Bag of Words, TF IDF… no context!






● We add in context with N-gram models






● We add in context with N-gram models

● We extended these with CBOW and Skip-grams

○ CBOW: Predict center word

○ Skip-grams: Predict surrounding words

• So far, we have an expression for the chance that a sequence of

words appears as products of conditional probabilities

• Now, we’d like models that can learn the probabilities of word-

sequences

• Solution: Word2vec (Mikolov et al, 2013)

Learning word-sequence probabilities

Word2vec• A neural network implementation that learns distributed representations

for words

• 2 algorithms

• Continuous bag of words

• Skip-grams

• 2 training methods

• Negative sampling

• Hierarchical softmax

• Best part: DOES NOT NEED LABELED DATA!

Word2vec

• Many of those steps are complicated...

• Luckily, someone made software that does this for us

• Gensim is a python package that can do all of this complicating

word2vec stuff in a few lines of code

• Results: Training high dimensional word vectors on a large amount of

data captures “Subtle semantic relationships between words”

Reflecting on word2vec• Words with similar meanings occur in clusters

• Clusters are spaced such that some word relationships (such as

analogies) can be reproduced with vector math

• Famous example (with highly trained word vectors)

• “king” - “man” + “woman” = “queen”

• Useful feature: word2vec does not require labeled data

• Most data in the world is unlabeled!

• Word embeddings are very useful for prediction and translation tasks, as

well as sentiment analysis


• Grammars


• Modern NLP


• NLP in Industry

• Demos

Modern NLP• Advances in NLP were largely driven by

• A vast increase in computing power• A better understanding of human language• Development of successful ML algorithms• Big data

• Much of current work involves:• Machine translation• Spoken dialogue and conversational agents• Machine reading• Mining social media• Analysis and generation of speaker state

Forms of NLP DataUser data Corpora

Dictionaries

Ontologies and databases

NLP Data Sources• Wikimedia

• APIs: Twitter, Wordnik, …

• Common crawl

• Wordnet

• Linguistic data consortium (www.ldc.upenn.edu)

• University sites and the academic community

• Stanford, Oxford, CMU

• Create your own!

• Web-scrape, crowd-source, linguists

http://www.ldc.upenn.edu

Deep Learning vs Non-deep Learning Methods

• Bag of words may outperform deep learning models in

modest sized datasets

• Word2vec sees a drastic improvement with a LOT of text

• In literature, distributed word vector techniques outperform

bag of words models

Deep learning tries to capture the recursive nature of natural language

Deep Learning for NLP• Deep learning attempts to learn multiple levels of representation of increasing

complexity and abstraction

• Want computers to be able to understand the recursive nature of human

language

• Recursive/recurrent neural networks!

• DL models can be fast ways to solve NLP tasks

Recurrent Neural Network● Recurrent Neural Network

○ Connections between units

form are directed cycles

○ Internal state of the network

allows it to exhibit dynamic

temporal behavior

○ Success in speech recognition,

natural language, translation,

etc.

● Long Short-term Memory: LSTM

Recurrent Neural Network

seq2seq● Applied RNNs to Sequences

○ Generate a response based on meaningful input

○ For example, translate from English to French

● Two RNNs: an encoder that processes the input and a decoder that generates the

output.

Recursive Deep Learning• Compositional vector grammars (parsing)

• Recursive autoencoders (paraphrase detection)

• Matrix-vector RNNs (relation classification)

• Recursive neural tensor networks (sentiment analysis)

What’s at UC Berkeley?• Berkeley NLP Research - Dan Klein

• Computer Vision - Alexei Efros, Jitendra Malik

CV + NLP: Visual Question Answer


• Grammars


• Modern NLP


• NLP in Industry

• Demos

What the (near) future holds

Bots!Think Siri, but actually functional instead of a toy

What the (near) future holdsSupporting invisible UI!

The concept of invisible or zero user interaction between user and machine

What the (near) future holdsSmarter search!

The same capabilities that allow a chatbox to understand a customer’s request can enable “search like you talk” functionality

What the (near) future holdsIntelligence from unstructured information!

Analysis that accurately understands the subtleties of natural language (choice of words, tone, etc) can provide useful knowledge and insight of

information


• Grammars


• Modern NLP


• NLP in Industry

• Demos

NLP in Industry

NLP Architectures• Layered Model

• Preprocessing• Low-level analysis• Semantic Analysis• Conversion to end products

• Input/Output as API Structure

NLP at Scale• Systems come before algorithms

• Objective functions are messy

• Everything is changing

• Understanding-optimization trade-off

NLP at Scale• Systems come before algorithms

• Objective functions are messy

• Everything is changing

• Understanding-optimization trade-off

Developing an NLP system

1. Exploration

a. Translate real-world requirements

into a measurable goal

b. Find an appropriate level and

representation

c. Find data for experiments


1. Exploration

a. Translate real-world requirements into

a measurable goal


representation


2. Development

a. Find and utilize existing tools and

frameworks

b. Set up and perform a series of

experiments


1. Exploration

a. Translate real-world requirements into

a measurable goal


representation


2. Development

a. Find and utilize existing tools and

frameworks

b. Set up and perform a series of

experiments

3. Production

a. CPU/GPU intensive

b. Most NLP frameworks

are not production-ready

c. Pre- and post-

processing is invaluable

d. Collect user feedback

I Have the Model… Now What?1. Specify Performance Requirements

2. Separate Prediction Algorithm From Model

Coefficients

a. Select or Implement The Prediction Algorithm

b. Serialize Your Model Coefficients

3. Develop Automated Tests For Your Model

4. Develop Back-Testing and Now-Testing

Infrastructure

5. Challenge Then Trial Model Updates

Tips for NLP• Proper preprocessing is VERY important

• Know your domain!

• Validate your models!

• Human judges

• Cross-validation


• Grammars


• Modern NLP


• NLP in Industry

• Demo

Programming Language Identification

Exploring code on GitHub

Goal is to figure out what language a file uses

Potential Methods?

Filename, keywords, comments

Whitespace, syntax

Must be scalable to handle large number of constantly updating repos

Existing Model

Linguist: Heuristics + Naive Bayes

Heuristics can be accurate but require updating and fine-tuning

Naive Bayes depends on word frequencies - predictions are linear to vocab size

Hard-coded rules do most of the work, leaving the Naive Bayes as a last resort

Heavily dependent on file extension classification

Selective Classification

With file extensions, only 87% of files are classified

Thank you!

[email protected]

Special thanks to Jordan Prosky

mailto:[email protected]

Appendix

Appendix• Language is meant to convey meaning, which we have a natural

way of encoding

• Children learn this very fast!

• Hard for computers to learn…

• Language is a symbolic signaling system

• Example: pen: or ?

• Other subtleties: sarcasm, expressive signaling, …

What makes NLP difficult?• Language is meant to convey meaning, which we have a natural

way of encoding

• Children learn this very fast!

• Hard for computers to learn…

• Language is a symbolic signaling system

• Example: pen: or ?

• Other subtleties: sarcasm, expressive signaling, …

Basics of NLP data preprocessing

• Domain specific!

• Tokenization

• Example: “This is a test that isn’t so simple”

• Tokens: “This”, “is”, “a”, “test”, “that”, “is”, “n’t”, “so”,

“simple”

• Regular expressions

• Stemming

• Lower-casing

• Removing/adding punctuation

• Other…

SVD-Based Methods• Loop over a massive dataset to accumulate word co-occurrence counts in

some matrix X

• Perform the SVD on X to get U, S, and V

• Use the rows of U as the word embeddings for all words in your dictionary

X = ?

SVD-Based Methods: Word-Document Matrix

• Assumption: related words often appear in the same document

• Loop over many documents and every time word i appears in

document j, add one to entry Xij

• Very high dimensional - let’s try something better

We are not quite done…• Need to find suitable U and V matrices!

• Two algorithms help us get what we want:

• Hierarchical softmax

• Negative sampling

• These are complicated!

• Luckily, someone made software that does this for us

• Gensim is a python package that can do all of this complicating

word2vec stuff in a few lines of code

Data & Analytics

A Panorama of Natural Language Processing