SRU- Search/Retrieve via URL - is a standard XML-based protocol for search queries, utilizing CQL - Contextual Query Language - a standard syntax for representing queries.
SRU 2.0 SRU 1.2 SRU 1.1 CQL
Version 1.1 was released in 2004 and 1.2 in 2007. SRU 2.0 is an OASIS Standard.
Scan Explain SRW XML Files
The Library of Congress » Standards » SRU
July 29, 2016