Book catalog retrieval system opac belongs to query system. Opac is the abbreviation of online Public Access Catalogue, that is, "online public bibliography retrieval system", which is an electronic catalogue query service provided by the library to readers. Readers can retrieve the library's bibliography and related information about OPAC, and also log in to my library to renew books online, inquire about personal borrowing, make appointments and report the loss. The OPAC system interface is as follows:

OPAC system has nine functions: bibliographic retrieval, popular recommendation, classified browsing, new book notification, periodical navigation, reader recommendation, subject reference, information release and my library.

OPAC system is a good library public retrieval system, which has many functions and is clear, and is also used by many universities.