VMS Help SCA, SCA Topics, Libraries, Virtual Libraries  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    SCA can use more than one SCA library at the same time when doing
    queries using the FIND and INSPECT commands. The list of SCA
    libraries used for this is called a virtual library. The order
    of SCA libraries in the library list is important. A module in
    the first library in the library list will hide the same module
    in other libraries, further on in the library list. For example,
    suppose PROJECT_LIB has modules A, B, C and library MYLIB has
    modules A, and D. You can set the library as follows:

      LSE Command> SET LIBRARY mylib,project_lib

    The modules visible in the virtual library would be A (from
    MYLIB), B, and C (both from PROJECT_LIB) and D (from MYLIB).

    There are many reasons for using more than one physical library as
    your virtual library:

    o  Using more than one library, you can improve LOAD performance
       by loading multiple libraries simultaneously. See the help
       topic Reducing_LOAD_Time.

    o  You can use virtual libraries to allow several developers to
       maintain a consistent view of their changes to a project,
       without affecting the other developers, and without having
       to copy the entire SCA library for each developer.

    o  You can put your SCA libraries on different disks or on
       different nodes (using the SCA server). This improves
       performance or takes advantage of the available disk space.

    o  You use the SET LIBRARY and SET NOLIBRARY commands to maintain
       your virtual library list. You can use the /BEFORE and /AFTER
       qualifiers to insert and remove libraries without having to
       reenter a library list. You can specify libraries in your
       library list using library numbers. For example, the command
       SET NOLIBRARY 2 removes the second SCA library from the library
       list.