AS/400 Library

A library (*LIB) on the AS/400 is an object that is used as a system directory to keep track of other objects. 

OR

In AS/400 a library is an object that can contain other objects (executable objects, source files, etc.).

Library is used to find other OS/400 objects in the database. To find an OS/400 object you need the name of the library and the name of the object.  

The AS/400 identifies objects by their qualified name, which takes the form of LIBRARY/OBJECT.  

Some important Points:

• The AS/400 library is organized as a single-level hierarchy.
• An object can exist in only one library.
• Two or more objects can have the same name but they must be different types of objects.
• A library cannot reference other libraries except for the library called QSYS. This is the only library that can access other libraries.

Certain types of the AS/400 object (database file, storage areas and executable program objects) can be compiled, copied, and stored into/from many different libraries concurrently, with the Library List hierarchy determining which instance of the object to use during execution of any application that utilizes that object name. 

Generally speaking all libraries created by IBM for use by the operating system begin with the letter 'Q'.

Some IBM Standard Libraries:

QSYS -          System Parent Library
QSYS2 -        System Library for CPI's
QHLPSYS -  Online Documentation Library for Users
QTCP -          TCP Connectivity Utilities
QAFP -          Advanced Function Printing
QGPL -         General Purpose Library
QTEMP -      Job specific temporary Library (deleted when the job ends)


References:

• http://en.wikipedia.org/wiki/AS/400_library
• http://pic.dhe.ibm.com/infocenter/iseries/v7r1m0/index.jsp?topic=%2Frbam6%2Frbam6objects.htm