Object-Based - IBM eserver i5 Handbook

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Note: IBM i5/OS for V5R2 and earlier versions is called OS/400.
After you buy an iSeries server, you do not have to continue shopping for system
software components before the server is ready to run your business. All of the
software factors for a relational database, comprehensive security,
communications with a broad range of diverse systems, including Internet
capabilities, and many more components are already in the operating system.
Each is fully integrated into i5/OS. By "fully integrated", we mean fully tested, too.
All components and prerequisites for running business applications in the new
century work together, and are fully tested together. i5/OS operates as a single
entity.
On the iSeries servers, high-level machine instructions execute only on what they
are designed for. Only a program (an object) can be executed. Data (also an
object) can be read, updated, or deleted, but cannot be executed (a common
technique for introducing viruses on other architectures).

Object-based

An object is a container. Everything the system uses (user and system data
structures) is packaged in one of these containers. The objects are
encapsulated, which means that you cannot see inside. The list of valid ways in
which that object can be used is inseparable from an object.
There are two important consequences of an object-based design. The first is
that a system built around an object model supports machine independence.
This means that technology changes can be made in the environment without
affecting application programs. The second consequence is that an object-based
design delivers an inherently high level of system integrity and security.
All objects are structured with a common object header and a functional portion
dependent on object type. Therefore, on the iSeries servers, instructions work on
only what they are supposed to work. Data cannot be treated as executable code
(so that the processor cannot try, for example, to execute someone's shoe size).
Executable code cannot be treated as data by having something written into the
middle of it.
OS/400 distinguishes between user and system programs. Certain instructions
apply to all objects, while other instructions work only on specific types of
objects. Therefore, it is not possible for valid programs to misuse an object, unlike
the situation that exists for non-iSeries systems without an object-based
approach. The iSeries remains virus-resistant with features such as this.
IBM Eserver i5 and iSeries System Handbook
34
Draft Document for Review October 18, 2004