The definition of word embedding:
https://en.wikipedia.org/wiki/Word_embedding. 

University of Michigan - Ann Arbor

Rather than representing words as discrete variables, word embeddings map words into low-dimensional real-valued vectors. This continuous representation space makes it possible to compute the meanings of words and word $$n$$-grams. As a result of this distributed representation, language models are no longer burdened with the curse of dimensionality, allowing them to represent exponentially many $$n$$-grams via a compact and dense neural model.

Word embedding

Qiu, X., Sun, T., Xu, Y., Shao, Y., Dai, N., & Huang, X. (2020). Pre-trained models for natural language processing: A survey. Science China Technological Sciences, 63(10), 1872-1897.

https://arxiv.org/abs/2003.08271. 

Pre-trained Models for Natural Language Processing: A Survey

Word embedding (NLP) definition

Most of the encoders can be categorized as sequence and non-sequence models.

- Sequence models: Capture a word's local context in sequential order. Examples: convolutional models (capture the meaning of words by aggregating information from neighbors), recurrent models (capture contextual representations with short memory). They learn the contextual representation of the word with locality bias, but are easy to train.
- Non-sequence models: Learn the contextual representation with a pre-defined tree or graph structure between words. Example: Fully-connected self-attention model (Use a fully-connected graph to model the relation of every two words and let the model learn the structure by itself).


Neural contextual encoders

- Non-contextual embeddings: Word representations learned by neural network language models are able to capture linguistic regularities in language, and the relationship between words can be characterized by a relation specific vector offset.

Model analysis: Knowledge captured by PTMs

The concept of learning word representations from neural language models, while inspiring, was not immediately adopted for building NLP systems. A pivotal change occurred around 2012 with the emergence of efficient techniques like Word2Vec. These methods enabled the learning of word embeddings from massive text corpora through simple word prediction tasks, leading to their successful and widespread integration into a variety of NLP applications.

Evolution of Word Embedding Techniques

Building on the success of representing individual words as vectors, the research focus in NLP expanded to learning representations for entire sequences of text. This progression was enabled by more powerful language models, such as those using LSTM architectures. The subsequent introduction of the Transformer model dramatically accelerated this trend, causing a surge in research and development of sequence representation techniques.

Shift from Word to Sequence Representations

Although the concept of learning word representations from neural language models was influential and inspired further research, it was not widely adopted in practical NLP systems for several years. A major turning point occurred around 2012 with the advent of efficient methods like Word2Vec. These techniques facilitated learning embeddings from massive text corpora through simple word prediction tasks, leading to their successful and widespread application across the field.

Evolution and Adoption of Word Embeddings

An engineer is developing a language model for a vocabulary of 100,000 unique words. They are considering two approaches for representing words as input to the model: a one-hot encoding scheme (where each word is a 100,000-dimensional vector with a single '1' and the rest '0's) and a pre-trained 300-dimensional word embedding scheme. Which of the following statements provides the most accurate analysis of the primary advantage of using the word embedding approach in this scenario?

A simple method for representing words numerically is to assign a unique integer to each word in a vocabulary (e.g., 'cat' = 1, 'kitten' = 2, 'dog' = 3, 'puppy' = 4). Analyze the fundamental limitation of this integer-based approach for a model trying to understand relationships between words. Then, explain how representing words as multi-dimensional vectors addresses this limitation.

Analyzing Word Representation Methods

Based on the scenario below, propose a fundamental change to how words are represented as input to the model to solve the described problem. Justify your proposal by explaining why the current method fails and how your proposed method would lead to better performance.

Improving Model Generalization

The initial idea of learning word representations through neural language models inspired research into representation learning in NLP, though it did not attract significant interest at first. However, starting around 2012, advances were made in learning word embeddings from large-scale text via simple word prediction tasks. Several methods, such as Word2Vec, were proposed to effectively learn such embeddings, which were subsequently applied with great success across various NLP systems.

Learning Word Embeddings via Word Prediction Tasks

Following the successful application of word embeddings via simple prediction tasks, researchers began to explore learning representations of entire sequences using more powerful language models, such as LSTM-based models. Further progress and immense interest in sequence representation exploded after the Transformer architecture was proposed.

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