An online public access catalog (often abbreviated as OPAC or simply "library catalog") is an online database of materials held by a library or group of libraries. Users typically search a library catalog to locate books, periodicals, audio/visual materials or other items under control of a library.
As access to the internet became more accessible to more people library users have grown more and more accustomed to these sites and search engines. They have become increasingly dissatisfied with the search mechanisms of older library catalog systems. This has, in turn, led to vocal criticisms of these systems within the library community itself, and in recent years to the development of newer (often termed 'next-generation') catalogs. However, the large cost associated with these new systems has significantly hindered the widespread use of new systems.
The newest generation of library catalog systems are distinguished from earlier OPACs by their use of more sophisticated search technologies, in particular faceted search, and features aimed at greater user interaction and participation with the system, including tagging, reviewing, and RSS feeds.
However, the usefulness of these catalogs is limited by inconsistent metadata standards that vary from publisher to publisher. There is also the concern that only newly digitized material can be found while older material, published on different platforms that are no longer supported is effectively lost. Libraries are then faced with the expensive and time-consuming task of reapplying new metadata tags to ensure these older records can become discoverable. At present there is no single standard for metadata records.
See below for a list of some next generation library catalog systems.