IBM i 五大特色之二 Object-based Design

IBM i 五大特色之二 Object-based Design

Object-based Design

The IBM i is a fully object-based system. This means that everything within the system — programs, data files, message queues — is an object. Each object has two inseparable parts: a descriptive part, which defines the valid ways of using that data, and a data part, which serves as the functional aspect of the object. For example, if an object is defined as a program, its descriptive part states that the data part will be treated as executable, read-only, compiled code. The only operations allowed on this object are those that make sense for a program. For example, you can write into the middle of a data file, but you can’t write into the middle of compiled code; the system won’t let it happen. Thus, IBM i objects’ two-part design ensures data integrity for all objects in the system.

Object-based design has important security implications. For example, one mechanism by which computer viruses enter systems is by masquerading as data. Then, after they’re inside, they try to become executable code and wreak havoc. Such a change of characteristics isn’t possible on the IBM i ; if the system lets a package enter the system as data, that package must retain the characteristics of data forever. It can’t change its mind and become executable code.