Contextual Query Language (CQL), previously known as Common Query Language, is a formal language for representing queries to information retrieval systems such as search engines, bibliographic catalogs and museum collection information. Based on the semantics of Z39.50, its design objective is that queries be human readable and writable, and that the language be intuitive while maintaining the expressiveness of more complex query languages. It is being developed and maintained by the Z39.50 Maintenance Agency, part of the Library of Congress.

Simple queries:

Queries accessing publication indexes:

Queries based on the proximity of words to each other in a document:

Queries across multiple dimensions:

Queries based on relevance:

The latter example specifies using a specific algorithm for logistic regression.

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