Book Image

Natural Language Processing with Flair

By : Tadej Magajna
Book Image

Natural Language Processing with Flair

By: Tadej Magajna

Overview of this book

Flair is an easy-to-understand natural language processing (NLP) framework designed to facilitate training and distribution of state-of-the-art NLP models for named entity recognition, part-of-speech tagging, and text classification. Flair is also a text embedding library for combining different types of embeddings, such as document embeddings, Transformer embeddings, and the proposed Flair embeddings. Natural Language Processing with Flair takes a hands-on approach to explaining and solving real-world NLP problems. You'll begin by installing Flair and learning about the basic NLP concepts and terminology. You will explore Flair's extensive features, such as sequence tagging, text classification, and word embeddings, through practical exercises. As you advance, you will train your own sequence labeling and text classification models and learn how to use hyperparameter tuning in order to choose the right training parameters. You will learn about the idea behind one-shot and few-shot learning through a novel text classification technique TARS. Finally, you will solve several real-world NLP problems through hands-on exercises, as well as learn how to deploy Flair models to production. By the end of this Flair book, you'll have developed a thorough understanding of typical NLP problems and you’ll be able to solve them with Flair.
Table of Contents (15 chapters)
1
Part 1: Understanding and Solving NLP with Flair
6
Part 2: Deep Dive into Flair – Training Custom Models
11
Part 3: Real-World Applications with Flair

Sequence labeling metrics

When comparing one sequence tagger to another, we can't simply try them out by hand and take a wild guess about which one performs better. Their performance needs to be evaluated using the same dataset and computed using the same predefined metric. The most common metrics used in sequence labeling are accuracy and F1 score.

Measuring accuracy for sequence labeling tasks

Accuracy is a measure ranging from 0 to 1 that simply computes the proportion of correctly tagged tokens.

Assuming correctly_tagged_tokens is the number of correctly tagged tokens and all_tokens is the total number of all tokens, accuracy can be defined as:

The preceding formula is simple and provides an easily interpretable result, but the metric can be misleading when dealing with imbalanced datasets (datasets where classes/tag names are not represented equally). This is particularly noticeable with NER where the majority of tokens belongs to a single class. For example...