A Common Model of Systems and Devices

Web-Based Enterprise Management (WBEM) is a set of standards, developed by the DMTF, to unify the management of enterprise computing environments, allowing a variety of information processing elements from different vendors to be managed in a uniform way. Systems managed with WBEM may be general-purpose computer systems running any operating system, or they may be printers, network switches or routers, storage arrays, or any other device reachable on a network.

WBEM goes beyond similar network management standards such as SNMP and DMI, and defines the following specifications:

The CIM standard specifies a model (or representation) for management data. It defines a set of objects (or classes) that are commonly found in information-processing environments. CIM has representations for entities such as disks, files, user accounts, memory, video cards, software, processes, queues, and many other familiar concepts.

The standard also specifies operations that can be performed on these objects. A set of operations that can be performed on any type of object is called the intrinsic methods, and includes accessing, creating and deleting instances of these objects; modifying specific properties; and so forth. Additional operations, called extrinsic methods, are defined for specific classes of objects. The definition for the class CIM_LogicalDevice, for example, contains the extrinsic methods EnableDevice() and QuieseDevice(), which would not be meaningful when referring to an object such as a CIM_Account, which is used to represent a user's account.

Object definitions are organized in a hierarchy. The model features the object-oriented concept of inheritance, where a new class of object may be defined as "a kind of" an already defined class: a disk is a kind of device; a device is a kind of managed element, and so forth. The new class has all of the properties of its parent, or superclass, and possibly other properties of its own. All of its properties would in turn be inherited by any subclasses.

Inheritance offers an important benefit for client applications, since a client need not be developed to explicitly know about platform-specific features. For example, a client developed to manage user accounts could manipulate instances of a generic account object (CIM_Account), even though user accounts on different operating systems would typically be represented with additional, different properties. The platform-specific, fully represented account object would be defined as a subclass of CIM_Account (or one of its subclasses), but a request for all instances of CIM_Account would return the instances of subclasses, as well.

The model also describes associations between different objects. Associations are defined as classes, and therefore may also have properties and methods, and may make use of inheritance. An example of an association is the CIM_ControlledBy class, which allows a device to be associated with a device controller. In addition to pointers to the device and its associated controller, the definition for this class contains other information that is specific to the association itself, such as the selected data rate.

A hierarchy of object (or class) definitions resides in a namespace. A namespace can be thought of as a kind of directory or folder; namespaces themselves are organized hierarchically. HP WBEM Services for HP-UX is installed with the DMTF's CIM V2.5 class definitions preloaded in the root/cimv2 namespace. Other namespaces can exist on the same system, and can be used to manage separate sets of objects. The uses of namespaces and namespace security are described in more detail in the Appendix A: Appendix A “CIM Naming Guidelines” and in the “Security Architecture” section of Chapter 4.