Information Retrieval With Deep Autoencoders

Adam GibsonBlix.io

Zipfian Academy

Big Data Science 5-17-14

Overview

● Overview of IR and Question Answering Systems

● Overview of Deep Learning

● Tying the 2 together

Information Retrieval (IR) Overview

Components of an IR QA System

Data Ingestion and Indexing Types of Answers Relevance Measure Search Queries Types of Information Retrieval Answer Disambiguation

Data Ingestion and Indexing

Solr/Elastic Search/Lucene Focus on text: typically a custom process

for inputting data Indexing can be done on a per token

(per word) basis Typical preprocessing:

Named-entity recognition Relation extraction

Augment the index with certain kinds of information

Relevance Measure

Cosine similarity measures how “close” a document is to a query.

The query is vectorized via bag-of-words and compared to each document, also vectorized. This is done in light of TF-IDF.

Different Kinds of QA

Definition (Several relevant paragraphs concatenated in to one)

Direct Answer (Watson)

Interactive (Siri, voice assistants)

Question Answering Systems

Are a step beyond search engines…

Have several data sources from which a question can be answered

A classifier for the question type is used on the query

Several data sources can answer different kinds of questions

This is used to compile a list of question-answering candidates, or “documents most likely to succeed”.

Question Answering Systems (cont.)

Take the input text and classify it, to determine the type of question

Use different answer sources (search engines, triple stores/graph databases and computational engines such as Wolfram Alpha)

Compile a list of answer candidates from each source

Rank each answer candidate by relevance

Deep Learning with DBNs

Use Cases:● Any NLP (collobert and Weston 2011)● Sound with phonetics (asamir,gdahl,hinton)● Computer Vision (Lee, Grosse, Ng)● Watson (DeepQA)● Image search via object recogition (Google)● Recommendation Engines (Netflix)

Restricted Boltzmann Machines

● Units – Binary,Gaussian,Rectified Linear,Softmax,Multinomial● Hidden/Visible Units – Visible learns data – Hidden is partition

function● Contrastive Divergence is used for learning the weights● Positive phase: Learn inputs (Visible) Negative: Balance out

wrt partition function (Hidden)

Real Valued Inputs:

Binary Inputs:

Results – Feature Learning

More Results – Feature Learning

General Architecture

● Stacked Restricted Boltzmann Machines – Compose to learn higher level ● correlations in the data● Creates feature extractors

Use any sort of output layer with different objective functions to do different tasks:

● Logisitic/Softmax Regression – Negative Log likelihood classification● Mean Squared Error – Regression● Cross Entropy - Reconstructions

Deep Learning and QA Systems

Part of the problem with answer-candidate searches is speed: They’re slow.

Each question to be answered is computationally intensive.

Deep learning allows for fast lookup of various kinds of answer candidates by encoding them.

Deep autoencoders allow for the encoding and decoding of images as well as text.

Deep Autoencoders

Deep autoencoders are two deep-belief networks:

The first is a series of RBMs that encode the input into a very tiny set of numbers, also called the codes.

The codes are what’s indexed and stored in search.

The second DBN is the decoder, which reconstructs the results from the codes.

Architecture Visualization

The Encoding Layer: A How-To

Take the input, and make the parameters of the first hidden layer slightly bigger than that input. That allows for more information representation on the first layer.

Progressively decrease the hidden-layer sizes at each layer until you get to the final, coding, layer,

which is a small number (10-30 figures).

Make the final hidden-layer output be linear (i.e. real numbers). Linear is pass-through.

Decoding Layer

Transpose the matrices of the encoder and reverse the order of its layers.

Each parameter, after training the encoder, is used to create the decoding net.

The decoder’s hidden layers are the exact opposite of the encoder.

The output layer of the decoder is then trained to reconstruct the input.

Connecting the Dots

Deep autoencoders can assist in creating answer candidates for information-retrieval systems.

This works for image or text search.

This technique is called semantic hashing.

PCA Results

Some Results