Semantic Search

Component	Available Classes	Description
Ranker	SentenceTransformersRanker	Orders documents based on how relevant they are to the query. Example usage: In a query pipeline, after a keyword-based Retriever to rank the documents it returns.
Reader	FARMReader TransformersReader TableReader RCIReader	Finds an answer by selecting a text span in documents. Example usage: In a query pipeline when you want to know the location of the answer.
Retriever	BM25Retriever DensePassageRetriever TableTextRetriever EmbeddingRetriever TfidfRetriever	Fetches relevant documents from the DocumentStore. Example usage: Coupling Retriever with a Reader in a query pipeline to speed up the search (the Reader only goes through the documents it gets from the Retriever).
QuestionGenerator	QuestionGenerator	When given a document, it generates questions this document can answer. Example usage: Auto-suggested questions in your search app.