Character-based neural models have recently proven very useful for many NLP tasks. However, there is a gap of sophistication between methods for learning representations of sentences and words. While most character models for learning representations of sentences are deep and complex, models for learning representations of words are shallow and simple. Also, in spite of considerable research on learning character embeddings, it is still not clear which kind of architecture is the best for capturing character-to-word representations. To address these questions, we first investigate the gaps between methods for learning word and sentence representations. We conduct detailed experiments and comparisons of different state-of-the-art convolutional models, and also investigate the advantages and disadvantages of their constituents. Furthermore, we propose IntNet, a funnel-shaped wide convolutional neural architecture with no down-sampling for learning representations of the internal structure of words by composing their characters from limited, supervised training corpora. We evaluate our proposed model on six sequence labeling datasets, including named entity recognition, part-of-speech tagging, and syntactic chunking. Our in-depth analysis shows that IntNet significantly outperforms other character embedding models and obtains new state-of-the-art performance without relying on any external knowledge or resources.

Matching a seller listed item to an appropriate product has become a fundamental and one of the most significant step for e-commerce platforms for product based experience. It has a huge impact on making the search effective, search engine optimization, providing product reviews and product price estimation etc. along with many other advantages for a better user experience. As significant and vital it has become, the challenge to tackle the complexity has become huge with the exponential growth of individual and business sellers trading millions of products everyday. We explored two approaches; classification based on shallow neural network and similarity based on deep siamese network. These models outperform the baseline by more than 5% in term of accuracy and are capable of extremely efficient training and inference.

Hierarchical classification is a challenging problem yet bears a broad application in real-world tasks. Item categorization in the ecommerce domain is such an example. In a largescale industrial setting such as eBay, a vast amount of items need to be categorized into a large number of leaf categories, on top of which a complex topic hierarchy is defined. Other than the scale challenges, item data is extremely sparse and skewed distributed over categories, and exhibits heterogeneous characteristics across categories. A common strategy for hierarchical classification is the "gates-and-experts" methods, where a high-level classification is made first (the gates), followed by a low-level distinction (the experts). In this paper, we propose to leverage domain-specific feature generation and modeling techniques to greatly enhance the classification accuracy of the experts. In particular, we innovatively derive features to encode various rich domain knowledge and linguistic hints, and then adapt a SVM-based model to distinguish several very confusing category groups appeared as the performance bottleneck of a currently deployed live system at eBay. We use illustrative examples and empirical results to demonstrate the effectiveness of our approach, particularly the merit of smartly designed domainspecific features.

Unsupervised models can provide supplementary soft constraints to help classify new target data under the assumption that similar objects in the target set are more likely to share the same class label. Such models can also help detect possible differences between training and target distributions, which is useful in applications where concept drift may take place. This paper describes a Bayesian framework that takes as input class labels from existing classifiers (designed based on labeled data from the source domain), as well as cluster labels from a cluster ensemble operating solely on the target data to be classified, and yields a consensus labeling of the target data. This framework is particularly useful when the statistics of the target data drift or change from those of the training data. We also show that the proposed framework is privacy-aware and allows performing distributed learning when data/models have sharing restrictions. Experiments show that our framework can yield superior results to those provided by applying classifier ensembles only.