Investigating Bi-LSTM and CRF with POS Tag Embedding for Indonesian Named Entity Tagger
This work addresses named entity recognition for Indonesian language processing, but it is incremental as it applies existing deep learning methods to a new dataset.
The authors tackled the problem of Indonesian named entity tagging by investigating Bi-LSTM with POS tag embeddings and CRF vs. Softmax output layers, finding that POS tag embeddings improved performance, but both output layers had weaknesses in classifying tags.
Researches on Indonesian named entity (NE) tagger have been conducted since years ago. However, most did not use deep learning and instead employed traditional machine learning algorithms such as association rule, support vector machine, random forest, naïve bayes, etc. In those researches, word lists as gazetteers or clue words were provided to enhance the accuracy. Here, we attempt to employ deep learning in our Indonesian NE tagger. We use long short-term memory (LSTM) as the topology since it is the state-of-the-art of NE tagger. By using LSTM, we do not need a word list in order to enhance the accuracy. Basically, there are two main things that we investigate. The first is the output layer of the network: Softmax vs conditional random field (CRF). The second is the usage of part of speech (POS) tag embedding input layer. Using 8400 sentences as the training data and 97 sentences as the evaluation data, we find that using POS tag embedding as additional input improves the performance of our Indonesian NE tagger. As for the comparison between Softmax and CRF, we find that both architectures have a weakness in classifying an NE tag.