This article is part of a series titled ‘LLMs from Scratch’, a complete guide to understanding and building Large Language Models (LLMs). In this article, we discuss the self-attention mechanism and how it is used by transformers to create rich and context-aware transformer embeddings.
The Self-Attention mechanism is used to add context to learned embeddings, which are vectors representing each word in the input sequence. The process involves the following steps:
1. Learned Embeddings: These are the initial vector representations of words, learned during the training phase. The weights matrix, storing the learned embeddings, is stored in the first linear layer of the Transformer architecture.
2. Positional Encoding: This step adds positional information to the learned embeddings. Positional information helps the model understand the order of the words in the input sequence, as transformers process all words in parallel, and without this information, they would lose the order of the words.
3. Self-Attention: The core of the Self-Attention mechanism is to update the learned embeddings with context from the surrounding words in the input sequence. This mechanism determines which words provide context to other words, and this contextual information is used to produce the final contextualized embeddings.
With deep learning, the ROI for having clean and high quality data is immense, and this is realized in every phase of training. For context, the era right before BERT in the text classification world was one where you wanted an abundance of data, even at the expense of quality. It was more important to have representation via examples than for the examples to be perfect. This is because many Al systems did not use pre-trained embeddings (or they weren't any good, anyway) that could be leveraged by a model to apply practical generalizability. In 2018, BERT was a breakthrough for down-stream text tasks,
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