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How Transformer LLMs Work
Beginner
1h34m
Topics
Deep Learning
Embeddings
GenAI Applications
LLMOps
Machine Learning
NLP
RAG
Transformers
In the previous videos, we explored words and token embedding techniques, but with limited contextual capabilities. In this video, we will explore how you can encode and decode context with attention. Word2Vec create static embeddings. The same embedding is generated for the words "bank", regardless of the context. "Bank" can refer to both a financial bank as well as the bank of a river. Its meaning, and therefore its embedding should change depending on the context. Capturing the text context is important to perform some language tasks, such as translation. A step in encoding this text was achieved through recurrent neural networks or RNNs. These are variants of neural networks that can model sequences as an additional input. To do so, these RNNs are used for two tasks, encoding or representing an input sentence, and decoding, or generating an output sentence. Let's explore this by showcasing how this input sentence "I love llamas" gets translated to Dutch. The text is passed to the encoder, which attempts to represent the entire sequence through embeddings. The decoder then uses those embeddings to generate language. Here it translated the English "I love llamas" to the Dutch "Ik hou van lama's." Each step in this architecture is autoregressive. When generating the next words, this architecture needs to consume all previously generated words. For instance, you take the input "I love Llamas", the model then generates the first token, which "Ik", to then generate the next token, the output "Ik" is appended to the inputs. In step two, the input is now "I love llamas ik" , which in turn generates the output 'hou' You can continue this process at each step and continuously update the inputs with the previously generated token. Until the entire output is generated. Most models are autoregressive and will therefore generate a single token each time. Let's explore this encoding and decoding in a bit more detail. You again start with the input sentence. "I love llamas" tokenized into tokens. We can use Word2Vec to create the embeddings as the inputs. Although these embeddings are static by themselves, the encoder processes the entire sequence in one go and takes into account the context of the embeddings. The encoding step aims to represent the input as well as possible, and generates the context in the form of an embedding. This decoder in turn is in charge of generating language, and does so by leveraging the previously generated context embedding to eventually generate the outputs. As we explored previously, these output tokens are generated one at a time, which is called autoregressive. This context embedding, however, makes it difficult to deal with longer sentences, since it is merely a single embedding representing the entire input. So the single embedding might fail to capture the entire context of a long and a complex sequence. In 2014, a solution called attention was introduced that highly improved upon the original architecture. Attention allows the model to focus on parts of the input sequence that are relevant to one another, or attend to each other and amplify their signal. Attention selectively determines which words are most important in a given sentence. Take our inputs and outputs sequences, for example. Words with similar meaning like I and the Dutch Ik, which are synonyms, have higher attention weights since they are more related. I and llamas have lower attention weights since they do not relate much to each other in this particular sentence. And the same applies to all other words. By adding these attention mechanisms to the decoder step, the RNN can generate signals for each input word in the sequence related to the potential outputs. You can again represent the input using Word2Vec embeddings and pass those to the encoder. Instead of passing only a context embedding to the decoder, the hidden states of all input words are passed to the decoder. A stateful word is an internal vector from a hidden layer of an RNN that contains the information about the previous words. The decoder then uses the attention mechanism to look at the entire sequence. Finally, this again generates the language. Due to this attention mechanism, the output tends to be much better since you now look at the entire sequence using embeddings for each token or words instead of the smaller and more limited context embedding. So during generation, the model attends to the most relevant inputs. After having generated "Ik hou van" from using the inputs "I love llamas", the attention mechanism then highlights words that are more relevant in this particular example. The sequential nature of this architecture precludes parallelization during training of the model. Let's go to the next video and learn how attention is used in transformer models.
