IBM System i Overview

IBM System i platform is a midrange server offering by IBM. This machine has IBM proprietary operating system named IBM i. The database engine is integrated with the operating system. The database is called DB2 UDB for iSeries or simply DB2/400.

Basic Concepts

Integrated File System

The file system used on System i (iSeries) is called Integrated File System (IFS). IFS comprises of many different sub-file systems.

Object and Library

The native file system used by iSeries is QSYS.LIB. Each entity in this file system is an object.

Each object has an object type that is signified by a character string starting with '*' character. For example, an executable program object is signified by a character string *PGM, a service program object is signified by a character string *SRVPGM, and a data queue object is signified by a character string *DTAQ.

There is a special type of object called a library (signified by *LIB). Library objects are similar to directories in Microsoft Windows and UNIX systems. A library groups object of other types together. However, unlike a directory, a library cannot have another library as its child.

Objects such as files (tables), programs, and other native System i type objects can exist only inside a library. An object in a library is addressed as library_name/object_name.

Job and Library List

Each unit of work that is processed by the IBM System i is called a job. A job is uniquely identified by a job number assigned by the system when the job is started.

Each job has a library list associated with it. This is similar to PATH variable in Windows or LD_LIBRARY_PATH variable in UNIX. When an object is not explicitly qualified with a library name, the object is searched in the library list for the job. The first occurrence of the object in library list is used. A library list is signified by string *LIBL.

Data Queue

Data queues are a type of object on the IBM System i. Applications can send messages to the data queues, and the messages wait in data queues until be retrieved by other applications.