Densely Connected Bidirectional LSTM

Tensorflow implementation of Densely Connected Bidirectional LSTM with Applications to Sentence Classification, [arXiv:1802.00889].

Densely Connected Bidirectional LSTM (DC-Bi-LSTM) Overview

The architecture of DC-Bi-LSTM. The first-layer reading memory is obtained based on original input sequence, and second-layer reading memory based on the position-aligned concatenation of original input sequence and first-layer reading memory, and so on. Finally, get the n-th-layer reading memory and take it as the final feature representation for classification.

Illustration of (a) Deep Stacked Bi-LSTM and (b) DC-Bi-LSTM. Each black node denotes an input layer. Purple, green, and yellow nodes denote hidden layers. Orange nodes denote average pooling of forward or backward hidden layers. Each red node denotes a class. Ellipse represents the concatenation of its internal nodes. Solid lines denote the connections of two layers. Finally, dotted lines indicate the operation of copying.

Dataset Overview

More details of datasets are shown here: [dataset/raw/README.md]

Dataset	Classes	Average sentence length	Dataset size	Vocab size	Number of words present in word2vec	Test size
MR	2	20	10662	18765	16448	CV
SST1	5	18	11855	17836	16262	2210
SST2	2	19	9613	16185	14838	1821
Subj	2	23	10000	21323	17913	CV
TREC	6	10	5952	9592	9125	500
CR	2	19	3775	5340	5046	CV
MPQA	2	3	10606	6246	6083	CV

CV means cross validation

Usage

Configuration: all parameters and configurations are stored in models/config.py.
The first step is to prepare the required data (pre-trained word embeddings and raw datasets). The raw datasets are already included in this repository, which are located at dataset/raw/, word embeddings used in the paper, the 300-dimensional Glove vectors that were trained on 42 billion words, can be obtained by

$ cd dataset
$ ./download_emb.sh

After downloading the pre-trained word embeddings, run following to build training, development and testing dataset among all raw datasets, the built datasets will be stored in dataset/data/ directory.

$ cd dataset
$ python3 prepro.py

Then training model on a specific dataset via

$ python3 train_model.py --task <str> --resume_training <bool> --has_devset <bool>
# eg:
$ python3 train_model.py --task subj --resume_training True --has_devset False

If everything goes properly, then the training process will be launched

...
word embedding shape: [None, None, 350]
dense bi-lstm outputs shape: [None, None, 200]
average pooling outputs shape: [None, 200]
logits shape: [None, 2]
params number: 1443400
No checkpoint found in directory ./ckpt/subj/, cannot resume training. Do you want to start a new training session?
(y)es | (n)o: y
Start training...
Epoch  1/30:
45/45 [==============================] - 567s - train loss: 0.5043     
Testing model over TEST dataset: accuracy - 91.100
 -- new BEST score on TEST dataset: 91.100
...
Epoch  4/30:
45/45 [==============================] - 519s - train loss: 0.1998     
Testing model over TEST dataset: accuracy - 94.200
 -- new BEST score on TEST dataset: 94.200
Epoch  6/30:
45/45 [==============================] - 505s - train loss: 0.1534     
Testing model over TEST dataset: accuracy - 94.500
 -- new BEST score on TEST dataset: 94.500
Epoch  7/30:
45/45 [==============================] - 530s - train loss: 0.1415     
Testing model over TEST dataset: accuracy - 94.000
...

Results

Here only test the model on several datasets with some epochs to validate if the model works properly.

experiments on MacBook Pro (13-inch, 2017) with 3.1GHz Intel Core i5 CPU and 16GB 2133MHz LPDDR3 RAM

Dataset	Train Epochs	Batch Size	Dev	Test
MR	11 (w/o cross-validation)	200	N.A.	82.4
SST1	20	200	50.9	51.2
SST2	13	200	84.7	88.1
Subj	6 (w/o cross-validation)	200	N.A.	94.5
TREC	15	128	N.A.	94.7
CR	10 (w/o cross-validation)	64	N.A.	82.9
MPQA	5 (w/o cross-validation)	64	N.A.	87.3

the evaluation results on some datasets are slightly lower than those proposed in the paper may caused by data processing, different parameter settings (like, batch size, learning rate, learning rate decay, grad clip, char emb and etc.) or without applying cross-validation.