What is the role of embeddings in semantic IR?

Embeddings play a critical role in semantic information retrieval (IR) by enabling systems to understand and compare the meaning of text rather than relying solely on exact keyword matches. At their core, embeddings are numerical vector representations of words, phrases, or documents that capture semantic relationships. For example, the word “bank” might be represented as a vector that places it closer to “river” in one context (natural geography) and closer to “finance” in another (financial institutions). This allows IR systems to process queries and documents in a way that reflects their actual meaning, improving relevance even when terminology varies.

In practice, embeddings transform unstructured text into a mathematical form that machines can process. When a user submits a query, both the query and the documents in a database are converted into embedding vectors. Semantic similarity is then measured using mathematical operations like cosine similarity, which calculates the angle between vectors. For instance, a search for “canine companions” might retrieve documents containing “dogs” or “pets,” even if those exact terms aren’t present, because their embeddings share a similar direction in the vector space. This approach reduces dependency on rigid keyword matching and accounts for synonyms, related concepts, or contextual shifts in language.

Developers can implement embeddings using pre-trained models like Word2Vec, GloVe, or BERT, which generate vectors based on patterns learned from large text corpora. For example, BERT’s contextual embeddings analyze surrounding words to disambiguate meanings—like distinguishing between “Apple the company” and “apple the fruit.” Tools like FAISS or Annoy optimize the retrieval of similar vectors efficiently, even in large datasets. However, challenges include selecting the right embedding model for the domain (e.g., biomedical text vs. social media) and managing computational costs. By combining embeddings with techniques like approximate nearest neighbor search, developers can build IR systems that prioritize semantic relevance, enabling applications like improved search engines, recommendation systems, or question-answering tools.