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What is Word2Vec?

Word2Vec is an algorithm used in the field of natural language processing to convert words into numerical values. The aim is to ensure that the semantic meaning and content of the words are still captured in the vector so that the context of the paragraph is preserved. The idea behind this is based on the premise that words used in similar contexts also share a common meaning.

What is Word Embedding?

Word embedding describes various methods used in natural language processing (NLP) to convert words into numerical vectors that can be more easily processed by computers. The aim is to ensure that the numerical representation still contains essential information about the word, the context, and the meaning. These so-called word embeddings are an important starting point for the training of sentiment analysis, machine translation, or the recognition of entities in texts, such as location or time information.

The simplest approach to word embedding is known as one-hot encoding. This involves counting the number of unique words in a text and then filling a vector with this number of zeros. A word is then represented by the vector that has a one and not a zero at the position of the word in the sequence. However, this is a very primitive implementation that has a few problems to contend with. Firstly, the dimensionality of the vector quickly becomes very high and no semantic relationships between the words can be mapped.

One Hot Encoding Example
One-Hot Encoding Example | Source: Author

Other methods in word embedding attempt to circumvent these limitations by representing each word as a low-dimensional vector with continuous and non-binary values. Large amounts of text data and various unsupervised learning algorithms, such as Word2Vec, are used for this purpose. Typically, the resulting vectors have between 50 and 300 dimensions and are therefore computationally efficient.

Word embeddings are a central component when working with natural language. A lot of research has been done in this area in recent years, which is why there are already many pre-trained models that can be used directly for different languages.

What is Word2Vec?

Word2Vec is a widely used method from the field of word embedding that is becoming increasingly important and was developed by Google researchers back in 2013. It enables the creation of word vectors that convert semantic meaning and content into numerical values, which can then be used as input in other machine learning models.

Word2Vec is based on the idea that words have a similar meaning if they are used in similar contexts. This similarity must then be mapped with correspondingly similar vectors to form a high-dimensional vector representation.

Word Embedding
Low-Dimensional Space for Word Embeddings | Source: Author

How does Word2Vec work?

The Word2Vec approach uses a shallow neural network architecture to learn the word embeddings. The input layer accesses the one-hot vectors of words in the entire vocabulary. This input is passed on to the next layer, the hidden layer, which consists of a large number of neurons. These provide the high-dimensional vector representation of the word, as each neuron passes on a specific result that contains part of the word’s meaning.

Finally, the output layer consists of another group of neurons, the number of which ultimately determines the dimensionality of the vector. This output layer calculates a probability distribution over the words in the vocabulary to predict the so-called context words. These are words that are most likely to be used in the same context as the target word.

Word2Vec is usually based on one of two main architectures: Continuous Bag of Words (CBOW) or Skip-gram. The basis of the CBOW architecture is to predict the target word based on the context words, while the skip-gram architecture tries to predict the context words based on the target word. However, in many NLP tasks, the skip-gram architecture performs better, which is why it is used more often than the CBOW architecture.

How do Continuous Bag of Words and Skip-gram work?

Word2Vec is a popular method for training word vectors that can be used as input for machine learning models. The aim here is to convert the meaning and semantic context in which the word appears into a numerical value in the best possible way. This approach is based on a small neural network with an input layer, a hidden layer and an output layer. The weightings in the hidden layer, which are learned during training, later form the word vectors. There are now two different approaches to training, namely the Continuous Bag of Words (CBOW) approach and Skip-gram.

With CBOW, the model is trained by always passing a certain amount of so-called context words as input and the model aims to derive the target word from this. Sentences are taken from the text and a target word is determined. The surrounding words around the target word, the so-called context words, are then given as input to the model, which is now supposed to predict the corresponding target word. Just like the input layer, the output layer has the number of all unique words as the number of neurons, so that a one-hot encoded vector is created again. After training, the hidden layer, the so-called embedding layer, is used to produce word vectors.

The structure for the skip-gram approach is initially similar. The surrounding context words are formed for each target word. The number of words considered around the target word is freely selectable. The basic structure is also similar to that of the CBOW approach, with the difference that the target word is used as input rather than the context words. The model is then trained to predict the surrounding context words based on the target word. After training, the individual hidden layer is used again as a starting point to create the word vectors.

These are the two most commonly used approaches for Word2Vec and each has its strengths and weaknesses.

What are the applications of Word2Vec?

Pre-processing step for various applications. The models trained on it can be used for the following, for example:

  • Machine translation, i.e. the automated translation of a text into another language.
  • Chatbots are an interface for automated communication between a human and a machine. It must be possible to respond to the content-related questions of the human.
  • Text summarization is used to search through large amounts of text more quickly by simply reading a suitable summary. The latest models, such as GPT-3, can also create different summaries with different levels of difficulty.
  • Sentiment analysis: The generated word vectors can be used to train sentiment analyses that classify whether a text was written with a positive or negative sentiment. This is important, for example, when classifying customer reviews or social media comments.

Overall, Word2Vec is the key building block for many models in the field of natural language processing. Progress in this area has made many achievements in NLP possible in the first place.

What are the limitations and challenges of using Word2Vec?

Despite the great popularity and versatility of Word2Vec, there are some challenges and limitations that should be considered when using it:

  • Words not included in the vocabulary (OOV): The Word2Vec process can lead to inaccurate predictions when working with rare words that were not part of the original dataset. This can affect the performance of the models and their predictions.
  • The ambiguity of words: Each word can only have one embedding, i.e. one-word vector, which can lead to fuzziness for words with multiple meanings. Depending on the context, the meaning of the word changes, which cannot be sufficiently taken into account in a single vector.
  • Contextual understanding: Although Word2Vec uses mechanics to adequately capture the syntactic and semantic relationships between words, there can still be problems in achieving sufficient contextual understanding. The context words included are often not comprehensive enough to capture the full context of the text.
  • Distortions in the training data: When training Word2Vec, care should be taken to prepare the training data sufficiently to avoid including stereotypes and other sentiments in the training. Otherwise, the model will learn these distortions.
  • Computational resources: For large data sets with many different words, training a Word2Vec model can be very computationally intensive, which severely limits its applicability.

In conclusion, Word2Vec is a powerful tool when working with natural language, but it is important to be aware of these limitations and challenges when choosing a training method.

How does Word2Vec compare to other word embedding methods?

Word2Vec is not the only widely used word embedding technique. Over time, other powerful methods have evolved, a few of which are presented in this section:

  • GloVe (Global Vectors): This method is based on the basic idea of Word2Vec, but differs in mapping the semantic relationships between words using a co-occurrence matrix.
  • FastText: This is an extension of Word2Vec, which is characterized by the fact that it does not consider complete words, but so-called n-grams, i.e. sub-word units such as syllables or word stems.
  • ELMo (Embeddings from Language Models): This method uses a bidirectional LSTM network to generate word embeddings. This allows longer contexts to be taken into account in the language.
  • BERT (Bidirectional Encoder Representations from Transformers): In recent years, transformer-based architecture has become increasingly popular and is also used for word embeddings. A deeper contextual understanding is formed, which is based on the use of so-called attention layers.

Despite these competing methods, Word2Vec is still a popular procedure that impresses with its simplicity and effectiveness.

This is what you should take with you

  • Word2Vec is a widely used method in the field of natural language processing that enables a vector representation of words.
  • Contextual and semantic relationships between words are preserved as far as possible and are included in the numerical conversion.
  • Word2Vec has been shown to beat traditional approaches, such as bag-of-words, and has become a popular standard tool for this reason.
  • However, Word2Vec also has some limitations, such as dealing with rare words or capturing long contexts.
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You can find the documentation of TensorFlow about Word2Vec here.

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