From an OCLC Research Announcement:
SRU (Search and Retrieve via URL) 2.0 has been approved as a standard by the Organization for the Advancement of Structured Information Standards (OASIS). SRU is the web-based successor to Z39.50.
Functionality supported by SRU includes defining a standard query grammar for complex interoperable searching, the ability to specify the format of the documents returned and the mime-type of the response. SRU includes a capability to allow client software to query the server for functionality, include a complex description of the databases being searched.
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