SRW/U is an acronym for Search/Retrieve via the Web or URL and you might want to think of it as Sonne of Z39.50 sans the federated searching. Z39.50 is (was) a protocol -- a communication method -- for information retrieval. Originally designed to allow for the searching of remote databases, and while rather arcane, it truly was ahead of its time. (Much like the MARC record data structure, arcane but ahead if its time.)