virtual_library

   A library that allows you to split your SCA library into pieces.
   Each piece is called a physical library. SCA works the same way
   whether your virtual library has only one physical library or
   several physical libraries.

   Some of the reasons for using more than one physical library are
   as follows:

   o  Physical libraries can be placed on more than one disk, if
      there is not enough room on a single disk.

   o  Analysis date files can be loaded into more than one physical
      library at the same time, to make LOAD run faster.

   o  A small personal physical library can be used to keep track of
      your personal changes without affecting other users.

   o  A separate physical library can be used for each major
      component in your system.

   A single virtual library is a list of one or more physical
   libraries. The order is important. A module in one physical
   library hides the same module in physical libraries later on in
   the list. This list of physical libraries is called a library
   list.