What are transformers in NLP?

Transformers are a type of neural network architecture designed for processing sequential data, such as text, and have become the foundation for most modern natural language processing (NLP) systems. Introduced in the 2017 paper “Attention Is All You Need,” transformers address limitations of earlier models like recurrent neural networks (RNNs) and long short-term memory (LSTM) networks. The core innovation of transformers is the self-attention mechanism, which allows the model to weigh the importance of different words in a sentence relative to each other. Unlike RNNs, which process text sequentially, transformers analyze all words in a sentence simultaneously, making them more efficient for parallel computation. This design enables better handling of long-range dependencies—relationships between words that are far apart in a sentence—which is critical for tasks like translation or summarization.

The transformer architecture consists of two main components: an encoder and a decoder. Each encoder layer includes a self-attention mechanism followed by a feed-forward neural network. The self-attention step computes attention scores between every pair of words in the input, determining how much focus each word should receive when processing another. For example, in the sentence “The cat sat on the mat,” the word “cat” would have a stronger connection to “sat” than to “mat.” The decoder uses similar layers but adds a masked self-attention step to prevent the model from “peeking” at future words during training. Positional encodings are also added to the input embeddings to give the model information about word order, since transformers lack inherent sequential processing. Multi-head attention, a variant of self-attention, splits the input into multiple subspaces, allowing the model to learn diverse relationships (e.g., syntactic vs. semantic patterns).

Transformers have driven significant advancements in NLP. For example, models like BERT use bidirectional training to understand context from both directions, making them effective for tasks like question answering. GPT-style models use the decoder stack to generate coherent text by predicting the next word in a sequence. Libraries like Hugging Face’s Transformers provide pre-trained models that developers can fine-tune for specific applications, such as sentiment analysis or named entity recognition. A key advantage is scalability: larger transformer models (e.g., GPT-3) achieve better performance by increasing parameters and training data. However, this comes with higher computational costs. Despite this, transformers remain practical because their parallel processing reduces training time compared to RNNs. For developers, understanding transformers is essential for working with modern NLP tools, whether building chatbots, improving search engines, or automating text analysis.