Named Entity Recognition by Neural Prediction

International audienceNamed entity recognition (NER) remains a very challenging problem essentially when the document, where we perform it, is handwritten and ancient. Traditional methods using regular expressions or those based on syntactic rules, work but are not generic because they require, for each dataset, additional work of adaptation. We propose here a recognition method by context exploitation and tag prediction. We use a pipeline model composed of two consecutive BLSTMs (Bidirectional Long-Short Term Memory). The first one is a BLSTM-CTC coupling to recognize the words in a text line using a sliding window and HOG features. The second BLSTM serves as a language model. It cleverly exploits the gates of the BLSTM memory cell by deploying some syntactic rules in order to store the content around the proper nouns. This operation allows it to predict the tag of the next word, depending on its context, which is followed gradually until the discovery of the named entity (NE). All the words of the context are used to help the prediction. We have tested this system on a private dataset of Philharmonie de Paris, for the extraction of proper nouns within sale music transactions as well as on the public IAM dataset. The results are satisfactory, compared to what exists in the literature

Spotting Keywords in Offline Handwritten Documents Using Hausdorff Edit Distance

Keyword spotting has become a crucial topic in handwritten document recognition, by enabling content-based retrieval of scanned documents using search terms. With a query keyword, one can search and index the digitized handwriting which in turn facilitates understanding of manuscripts. Common automated techniques address the keyword spotting problem through statistical representations. Structural representations such as graphs apprehend the complex structure of handwriting. However, they are rarely used, particularly for keyword spotting techniques, due to high computational costs. The graph edit distance, a powerful and versatile method for matching any type of labeled graph, has exponential time complexity to calculate the similarities of graphs. Hence, the use of graph edit distance is constrained to small size graphs. The recently developed Hausdorff edit distance algorithm approximates the graph edit distance with quadratic time complexity by efficiently matching local substructures. This dissertation speculates using Hausdorff edit distance could be a promising alternative to other template-based keyword spotting approaches in term of computational time and accuracy. Accordingly, the core contribution of this thesis is investigation and development of a graph-based keyword spotting technique based on the Hausdorff edit distance algorithm. The high representational power of graphs combined with the efficiency of the Hausdorff edit distance for graph matching achieves remarkable speedup as well as accuracy. In a comprehensive experimental evaluation, we demonstrate the solid performance of the proposed graph-based method when compared with state of the art, both, concerning precision and speed. The second contribution of this thesis is a keyword spotting technique which incorporates dynamic time warping and Hausdorff edit distance approaches. The structural representation of graph-based approach combined with statistical geometric features representation compliments each other in order to provide a more accurate system. The proposed system has been extensively evaluated with four types of handwriting graphs and geometric features vectors on benchmark datasets. The experiments demonstrate a performance boost in which outperforms individual systems