Query language

A Query language is a formal language that is used to make queries to database systems, and other information systems. The result of a query is a subset of the data. There are different query languages which target different user groups. It is possible to translate a query from one query language into another. 

XQuery is a query language to search XML information systems
XPath is used to navigate through XML documents
SQL is a query language commonly used for database systems
Query by Example was developed so that users who rarely use databases can also formulate queries.