从文本或数据库中，不限定数据字段，自由地萃取出消息的技术。

运行全文检索任务的程序，一般称作搜索引擎，它将用户随意输入的文本，试图从数据库中，找到符合的内容。

• 语根处理 (stemming)
• 符素解析器 (token parser) 1-gram, 2-gram , n-gram
• 断词/分词 word segmentation
• 反向索引 inverted index

In text retrieval, full text search refers to techniques for searching a single computer-stored document or a collection in a full text database. Full-text search is distinguished from searches based on metadata or on parts of the original texts represented in databases (such as titles, abstracts, selected sections, or bibliographical references).