Semantic Search

Semantic search is retrieval that matches a query to passages by meaning rather than by the words they share. The query and each passage are turned into vectors that encode what they are about, and the passages whose vectors sit closest to the query’s are returned, even when none of the query’s words appear in them.

How meaning gets compared

An embedding model maps a piece of text to a list of numbers, a vector, positioned so that texts about the same thing land near each other. At query time the question is embedded the same way and the store returns its nearest neighbours by a distance measure such as cosine similarity. Most production systems run this beside a keyword index and merge the two lists, because exact names, model numbers and addresses are things a keyword match gets right and a meaning match can blur. Retrieval-augmented generation is this step with a language model writing an answer from the top results.

What it changes for a page

Repeating the exact keyword matters less. A passage that states a specific thing plainly embeds close to the question that asks for it; a passage that talks around the subject embeds near nothing in particular. Pages are split into chunks before embedding, and each chunk is retrieved on its own, so a passage has to carry its subject with it (who, what, where) rather than relying on a heading three screens up. A sentence with a price, a service and a place in it is retrievable; a paragraph about quality and heritage is not, however well written.

A common question

If exact keywords matter less, what makes a passage findable by meaning alone?

Specificity, and carrying its own subject. A passage that states a particular thing plainly lands close to the question asking for it, while writing that circles a subject sits near nothing in particular. Pages are cut into chunks before they are embedded and each chunk is retrieved alone, so who, what and where have to travel inside the passage rather than sitting in a heading far above it. A sentence holding a price, a service and a place can be retrieved; a paragraph about heritage and quality cannot, however well it reads.

Sources

This entry states mechanism only and carries no figures. The measurement it feeds into is on the methodology page.