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Information Retrieval

Information Retrieval is the process through which a computer system can respond to a user's query for text-based information on a specific topic. IR was one of the first and remains one of the most important problems in the domain of natural laguague processing (NLP) - stanford cs276

This repo contains tutorials covering the breadth of techniques available for IR currently.

Along with IR techniques, we will also cover:

• Techniques/metrics for evaluating IR models.
• Approximate Nearest Neighbor techniques used for indexing and searching dense vectors (used for many dense retrieval techniques).
• Vector databases and other relevant info.

Tutorials

1. Classic Information Retrieval aka "The Inverted Index" [Notebook]

   IR in it's most basic form answers the question "how relevant is a given query for a document". The challenge is that we don't have just 1 document but potentially millions or billions of documents. So the key challenge is - how can we efficiently find this "needle in the haystack" or the "relevant documents for a query".

2. Evaluation metrics [Notebook]

   Binary: MRR, MAP@k; Graded: nDCG@k. The idea behind these evaluations is to quantitatively compare multiple IR models. Typically we have a labelled dataset where we have queries mapped to relvevant documents. The documents could either be graded or non-graded(binary). For example, a graded relevance score could be on a scale of 0-5 with 5 being the most relevant.

3. Dense representations and Finetuning BERT for IR / Semantic search [Notebook]

   Sparse represenation of texts using one-hot vectors is very limited. We look at ways to learn dense representations of text, from count based methods like LSA(TF_IDF+SVD) to Word2Vec to RNNs. Finally we look at how transformers are used in the IR setting.

4. Finetuning Sentence BERT(SBERT) with Multiple Negative Ranking loss [Notebook]

   We look at a better way to finetune Bi-Encoders using MNR loss. We will need lesser data and training to achieve better results.

5. Finetuning a Cross-Encoder [Notebook]

   We will look at Cross-Encoders. How they differ from Bi-Encoders. How to train them and when to use them.

6. Multilingual SBERT [Notebook]

   We see how knowledge distillation can be used to train a Multilingual Student sentence encoder using a Teacher model which has been finetuned for STS tasks.

7. Unsupervised training of SBERT - TSDAE [Notebook]

   We finally shift our attention to unsupervised techniques to train encoders for STS tasks with no labeled data. Here we look into TSDAE - Using Transformer-based Sequential Denoising Auto-Encoder for Unsupervised Sentence Embedding Learning.

8. Unsupervised training of SBERT - TSDAE (pytorch version) [Notebook]

9. Unsupervised training of SBERT - SimCSE [Notebook]

   We will look into SimCSE, a simple contrastive learning framework that works with both unlabeled and labeled data.

10. Unsupervised training of SBERT - GPL [Notebook]

    We will look into GPL, Generative Pseudo Labeling for Unsupervised Domain Adaptation of Dense Retrieval.