Task 5:

Aspect Based Sentiment Analysis (ABSA)

We focus on subtask1 first

Subtask 1: Sentence-level ABSA

Given a review text about a target entity (laptop, restaurant, etc.),

identify the following information:

• Slot 1: Aspect Category
  • ​ex. ''It is extremely portable and easily connects to WIFI at the library and elsewhere''
    ----->{LAPTOP#PORTABILITY}, {LAPTOP#CONNECTIVITY}
• Slot 2: Opinion Target Expression (OTE)
  • ​an expression used in the given text to refer to the reviewed E#A
  • ​ex. ''The fajitas were delicious, but expensive''
    ----->{FOOD#QUALITY, “fajitas”}, {FOOD#PRICES, “fajitas”}
• Slot 3: Sentiment Polarity
  • ​label: (positive, negative, or neutral) 

Paper Study

Latent Dirichlet Allocation
Topic Modeling

High input dimension seems not work...

1000 VS 3000

remove stopwords
stemming
tf-idf
simple word clustering...
not work  ... OTL

Find short descriptions of the members of a collection
whlie preserving the essential relationships

Introduction of Topic Modeling

Differ from tf-idf :

        tf-idf is is "indexing" (give proper weight to every unigram)

like normalization ... I think

Dimensionality Reduction

• Latent Semantic Indexing

use SVD to find subpace of tf-idf matrix that
capture most of the variance in the collection

• probablistic Latent Semantic Indexing

model each word as a sample of a mixture model

: hidden topic

Drawback of pLSI

• have no natural way to assign                for unseen documents

d is only a dummy label :p

• linear growth in params => overfitting issue

size grows in mixture(corpus)

We don't have generative model for portions of topic given arbitary document

Latent Dirichlet Allocation

Assumption : BOW (order of words can be neglected)

exchangeability

de Finetti's Theorem

Any collection of exchangeable RVs
has a representation as a mixture distribution

In our case , 
=>  word , topic is a mixture distrubution

And some hidden variable will determine those distribution

multinomial

Latent Dirichlet Allocation

(they are all "distribution over distributions")

Randomly choose corpus-level param
    for subsequent document-level param

decide topic dis.

use                to decide word probability conditioned on topic

Dirichlet is multi-nomimal version of beta distribution

Advantage : Avoid over-fitting issue in MLE (ref : CMU)

(conjugate to multinomial dis.)

Experiment in Slot1

After using PCA(SVD) to reduce dimension and get error ...
I found  I use sklearn's "fit_transform" incorrectly in previous ...

Experiment in Slot1 (Cross Validation)

Without LSI :

• With Tf-Idf indexing

restaurant : 61% (12 category)

laptop : 52% (81 category)

• Without Tf-Idf indexing

restaurant : 60% (12 category)

laptop : 50.05% (81 category)

Experiment in Slot1 (Cross Validation)

With LSI : (reduce dimension to 1000)

restaurant : 60% (12 category)

laptop : 52% (81 category)

Need more time...

Experiment in Slot1 (Cross Validation)

Bigram 

Trigram 

Experiment in Slot1 (Visualization of LSI)

Experiment in Slot1 (Visualization of LSI)

Experiment in Slot1 (Visualization of LSI)

Experiment in Slot1 (unsupervised LDA)

Experiment in Slot1 (supervised LDA)

Experiment in Slot1 (Summary)

Two kinds of classifier

• discriminative model : 

• generative model : 

use sample to classify directly

use sample to guess hidden model's param <learn a model>
use these models to predict unseen sample <classify>

Slot3 : Polarity Identification

Framework

Slot3 : 

Polarity Identification

Without using aspect information and removing conflicting polarities

Seems like we're on the right track...we hope so...

Problem we encountered

When modifying TreeLSTM code, the model can be trained on our dataset, but we can only feedforward data in the train and dev set, but not on the test set.

Our guess is that the dictionary was extracted from the train/dev data but not the test data, so some words in the test set cannot be encoded, causing the error