Question: What motivates the authors' work?
Evidence: Our work is motivated by three major threads of research in machine learning and natural language processing: semantic-parsing for open-domain question answering, character-level language modeling, and encoder-decoder methods.
Semantic parsing for open-domain question answering, which translates a question into a structured KB query, is a key component in question answering with a KB. While early approaches relied on building high-quality lexicons for domain-specific databases such as GeoQuery BIBREF7 , recent work has focused on building semantic parsing frameworks for general knowledge bases such as Freebase BIBREF1 , BIBREF8 , BIBREF0 , BIBREF9 , BIBREF2 .
Semantic parsing frameworks for large-scale knowledge bases have to be able to successfully generate queries for the millions of entities and thousands of predicates in the KB, many of which are unseen during training. To address this issue, recent work relies on producing embeddings for predicates and entities in a KB based on their textual descriptions BIBREF8 , BIBREF0 , BIBREF1 , BIBREF10 . A general interaction function can then be used to measure the semantic relevance of these embedded KB entries to the question and determine the most likely KB query.
Most of these approaches use word-level embeddings to encode entities and predicates, and therefore might suffer from the out-of-vocabulary (OOV) problem when they encounter unseen words during test time. Consequently, they often rely on significant data augmentation from sources such as Paralex BIBREF2 , which contains 18 million question-paraphrase pairs scraped from WikiAnswers, to have sufficient examples for each word they encounter BIBREF11 , BIBREF1 , BIBREF0 .
As opposed to word-level modeling, character-level modeling can be used to handle the OOV issue. While character-level modeling has not been applied to factoid question answering before, it has been successfully applied to information retrieval, machine translation, sentiment analysis, classification, and named entity recognition BIBREF12 , BIBREF13 , BIBREF6 , BIBREF14 , BIBREF15 , BIBREF16 , BIBREF17 , BIBREF18 , BIBREF19 . Moreover, gflstm demonstrate that gated-feedback LSTMs on top of character-level embeddings can capture long-term dependencies in language modeling.
Lastly, encoder-decoder networks have been applied to many structured machine learning tasks. First introduced in sutskever2014sequence, in an encoder-decoder network, a source sequence is first encoded with a recurrent neural network (RNN) into a fixed-length vector which intuitively captures its meaning, and then decoded into a desired target sequence. This approach and related memory-based or attention-based approaches have been successfully applied in diverse domains such as speech recognition, machine translation, image captioning, parsing, executing programs, and conversational dialogues BIBREF20 , BIBREF21 , BIBREF22 , BIBREF23 , BIBREF24 , BIBREF25 , BIBREF26 .
Unlike previous work, we formulate question answering as a problem of decoding the KB query given the question and KB entries which are encoded in embedding spaces. We therefore integrate the learning of question and KB embeddings in a unified encoder-decoder framework, where the whole system is optimized end-to-end.
Our work is motivated by three major threads of research in machine learning and natural language processing: semantic-parsing for open domain question answering, character-level language modeling, and encoder-decoder methods.
Answer: Three major threads of research in machine learning and natural language processing: semantic-parsing for open domain question answering, character-level language modeling, and encoder-decoder methods.