IBM i objects

An object is a named unit that exists (occupies space) in storage, and on which operations are performed by the operating system. IBM® i objects provide the means through which all data processing information is stored and processed by the IBM i operating system.

Objects are the basic units on which commands perform operations. For example, programs and files are objects. Through objects you can find, maintain, and process your data on the system. You need only to know what object and what function (command) you want to use; you do not need to know the storage address of your data to use it.

CL commands perform operations on the IBM i objects. Several types of IBM i objects are created and used in the control language. IBM i objects have the following characteristics in common:

• Objects have a set of descriptive attributes that are defined when the object is created.
• Objects that have to be used by the system to perform a specific function must be specified in the CL command that performs that function.
• Objects have a set of attributes that describe it and give the specific values assigned for those attributes.
• Generally, objects are independent of all other objects. However, some objects must be created before other objects can be created; for example, a logical file cannot be created if the physical file it must be based on does not exist.
• Objects must be created before other operations that use the object are performed. Descriptions of the create commands (those commands that begin with the letters CRT) give more information about the object types that they create.
• Every IBM i object that is used by the control language has a name. The object name specified in a CL command identifies which object is used by the operating system to perform the function of the command.
• Objects have either a simple, qualified, or generic name.

The system supports various unique types of objects. Some types identify objects common to many data processing systems, such as:

• Files
• Programs
• Commands
• Libraries
• Queues
• Modules
• Service programs

Other object types are less familiar, such as:

• User profiles
• Job descriptions
• Subsystem descriptions
• Device descriptions

Different object types have different operational characteristics. These differences make each object type unique. For example, because a file is an object that contains data, its operational characteristics differ from those of a program, which contains instructions.

Each object has a name. The object name and the object type are used to identify an object. The object name is assigned by the user creating the object. The object type is determined by the command used to create the object. For example, if a program was created and given the name OEUPDT (for order entry update), the program could always be referred to by that name. The system uses the object name (OEUPDT) and object type (program) to locate the object and perform operations on it. Several objects can have the same name, but they must either be different object types or be stored in different libraries.

The system maintains integrity by preventing the misuse of certain functions, depending on the object type. For example, the command CALL causes a program object to run. If you specified CALL and named a file, the command would fail unless there happened to be a program with the same name.