Online Public Access Catalogues (OPACs) 

Some of the cataloguing systems provided by software vendors usually contain some default OPAC program which can be utilised by the subscribing libraries to design their own OPACs to their specific libraries. The library can identify the individual library OPAC design and create separate menus both for staff as well as for the public (users of the library). 

Help messages are normally context-specific so that an appropriate message is displayed on the screen depending upon the stage that has been reached in search. Some of the systems allow the libraries to select the fields of the record for indexing. 

With the advent of GUI-based interfaces, it has become possible to include a range of information retrieval facilities in menus of OPACs. 

Recent developments in OPACs are related with public-access terminals in a Kiosk format and links to the Internet. Public-access terminals are generally based on touch screens. These Interfaces are reliant on menus in which the user selects his/her option by touching the screen. The range of search facilities is limited in the case of touch screens than in the case of terminals with keyboard access: Kiosks are designed for use in any location such as public libraries, shopping centres and railway stations. Some OPAC interfaces also offer an option which allows access to the Internet, through the same interface as is used for searching the library catalogue.