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Search for “a rainy-day activity” and a useful result might say “indoor things to do when the weather is bad.” An embedding model can help a search system recognize that those phrases are related, even though they share few exact words. It converts each text input into a vector—a list of numbers—so software can compare them.

What is an embedding?

An embedding is a numerical representation of an input, such as a word, sentence, image, or other data. For text, an embedding model turns the input into a vector, typically an array of floating-point numbers. Software can then compare that vector with others mathematically.

OpenAI describes embeddings as “numerical representations of concepts converted to number sequences, which make it easy for computers to understand the relationships between those concepts” in its January 25, 2022 announcement. Google Cloud similarly defines vector embeddings as numerical representations of data, typically arrays of floating-point numbers, in its vector database explainer.

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How does AI turn words into numbers?

An embedding model processes an input and produces a vector according to patterns it learned during training. Related inputs may end up closer together in the model’s vector space than unrelated ones. For example, OpenAI used “canine companions say” and “woof” as an illustration of phrases that are more related than “meow.”

Picture a map with just two or three axes: related items might appear near each other, while less related items appear farther apart. This is only an analogy. Real embedding spaces can have many dimensions, and their coordinates usually do not correspond to simple labels such as “happiness” or “sarcasm.” Google’s explanation of embedding space notes that real dimensions are rarely as easy to interpret as teaching examples.

The model’s output depends on the model and its intended task. Different models can represent inputs differently, so vectors from different models should not be assumed to be directly comparable. When choosing a model, check its supported inputs, language needs, task instructions, dimensions, and other current specifications. For example, Google’s Gemini embedding documentation describes different task settings and instructions for its embedding models.

How semantic search uses embeddings

Semantic search uses vectors to find passages that are related to a query, even when the wording differs. A basic system follows this flow:

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  1. Prepare the documents. Split documents into useful passages and use an embedding model to turn each passage into a vector. Keep the original text and any useful metadata alongside each vector.
  2. Embed the query. When someone searches, use the compatible model to turn the query into a vector.
  3. Rank nearby vectors. Compare the query vector with document vectors using a similarity or distance measure. The system ranks the closest candidates.
  4. Return the source text. Retrieve the original passages associated with the highest-ranked vectors. The vector helps locate the text; it does not replace it.

OpenAI’s embedding guide describes using separately generated query and document embeddings for search. Google Cloud explains nearest-neighbor search and vector indexing in its vector database overview.

Closeness is a relative similarity signal, not proof that two passages mean exactly the same thing or that either is correct. A passage may be close to a query while getting an important detail wrong. Systems should treat vector ranking as one part of retrieval, not a guarantee of truth.

When embeddings help—and when exact search matters

Embeddings are useful when people may describe the same idea in different words. They support semantic search, clustering, recommendations, classification, and anomaly detection, among other tasks, as listed in OpenAI’s current API guide.

Vector search can be weaker when the precise string matters: a product code, person’s name, legal clause, or exact phrase, for example. A practical search system can combine vector similarity with keyword search and metadata filters. Google Cloud documents hybrid vector and lexical search in its BigQuery introduction to embeddings and vector search.

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  • Use semantic matching when meaning may be expressed through varied wording.
  • Use exact keyword matching when a specific term, code, or name must appear.
  • Use metadata filters when results must meet a constraint such as category, date, or access permission.
  • Combine signals when both topical relevance and exact details matter.

What is a vector database?

A vector database stores embeddings and provides ways to index and search them. For a small collection, comparing a query vector with every stored vector may be practical. At larger scale, an index can make lookup faster. Approximate-nearest-neighbor methods trade some recall—the chance of finding every closest match—for faster retrieval. Google Cloud’s explainer covers nearest-neighbor search, approximate search, vector indexes, and metadata filtering.

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A dedicated vector database is one option. A database that already stores an application’s relational data and also supports vector search may be a better fit when keeping those operations together matters. The choice depends on data scale, filtering needs, latency, operational constraints, and how much recall the application requires.

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Embeddings do not write the answer

An embedding model produces a numerical representation; it does not, by itself, generate a written response. In a retrieval system, a search component can use embeddings to find relevant passages, then return those passages or pass them to a separate generative model to draft an answer. Google’s Gemini documentation distinguishes embedding models, which transform inputs into numerical representations, from generative models that create content.

What to check before building with embeddings

  • Task fit: Confirm the model and its instructions suit search, clustering, or the task you need.
  • Input and language support: Check what kinds of inputs and languages the model supports.
  • Vector compatibility: Use compatible model outputs for the query and stored documents; do not compare vectors from unrelated models by default.
  • Search behavior: Decide whether semantic ranking needs exact keyword matching, metadata filters, or both.
  • Scale and recall: Consider whether exact comparisons are sufficient or an approximate index is worth a possible reduction in recall.
  • Current specifications: Model dimensions, instructions, and normalization behavior vary and can change; consult the selected model’s documentation rather than relying on a generic fixed value.

For historical context, OpenAI’s January 2022 announcement reported results including a 20% relative improvement on its code-search benchmark comparison and a 99.85% data-source classification accuracy in a JetBrains Research example. These were company-reported results in particular settings, not guarantees for other datasets, models, or current systems. The same announcement includes examples from other named use cases, each tied to its own task and comparison.

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For developers who want a longer implementation-oriented introduction, O’Reilly’s Vector Databases: A Practical Introduction covers embeddings, semantic search, and a practical retrieval-augmented generation pipeline.

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