When patrons use libraries, they may use either
mediated or unmediated services (or library "products").
Mediated services involve the participation of library
staff, as in answering reference questions, performing
online searches, and circulating materials. Unmediated
services involve users interacting with systems and
products designed or selected by librarians, such as
library catalogs whether on cards or in online public
access (OPAC) format, paper or computerized indexes, stack
browsing, and reference materials. The librarian is absent
from these direct "end" uses.