z39.50 protocol it is not file.
Z39.50 is an international standard client–server, application layer communications protocol for searching and retrieving information from a database over a TCP/IP computer network. It is covered by ANSI/NISO standard Z39.50, and ISO standard 23950. Th
Z39.50 is widely used in library environments and is often incorporated into integrated library systems and personal bibliographic reference software. Interlibrary catalogue searches for interlibrary loan are often implemented with Z39.50 queries.
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