HP WBEM Services for HP-UX System Administrator Guide (5900-1624, April 2011)

A Representation of resources
The HP WBEM Services repository stores information about the managed resources.
To register with HP WBEM Services, a provider must define its resource by the classes and subclasses
that define it. Then the provider must describe the properties that it will expose, and the methods
that it will support.
The properties describe what a class is, the methods describe what it can do. Properties are
attributes or characteristics of the resource. Methods are its actions, capabilities, or behaviors.
To make a request, the client must first identify, by its classes and subclasses, the resource it wants
to manage.
The resource descriptions are done using object-oriented modeling. Object- oriented modeling
represents real things in an abstract schema. Objects are arranged from most general to most
specific. Many attributes of the more general parent are inherited by their more specific children.
Like object-oriented programming languages, the subclasses inherit the definitions of properties
and methods from the parent class. Unlike some object-oriented programming, they do not inherit
the implementations.
This section briefly describes basic concepts about object representation. As system administrator,
you do not need to understand this to install HP WBEM Services or maintain it. However, it is the
language that is used to explain resources. These are the terms that are used to describe what
providers and clients do, and how resources can be managed.
For more information about object representation, see the tutorial at: http://www.dmtf.org/
education/cimtutorial.php.
The schema is the most general abstraction that represents real things in the HP WBEM standard.
A schema is a collection of classes. Each class in a schema can only belong to that schema. Each
class name must be unique within a schema; a schema cannot have two classes with the same
name.
The class is the basic modeling unit. It is a collection or set of objects that have similar properties
and purposes. Each class defines a certain type of managed object, for example operating systems
or system memory. Objects in the class contain properties (describing what it is) and methods
(what it can do). A class can contain other classes (its subclasses). It can also contain instances.
Subclasses are grouped by similarities. Subclasses inherit properties and methods from their parent
(their superclass), and can also add their own local properties and methods. Subclasses are classes
and they can have their own subclasses.
CIM_SoftwareElement, for example, is a class. It has several subclasses, like HPUX_SoftwareElement,
Win32_SoftwareElement, and so on.
An instance can be a discrete occurrence of any object, such as your computer’s hard drive or the
printer on your desk. It is the specific member of the hierarchy. An instance cannot have any
subclasses. All instances in a class share the same properties and methods. Each instance has a
unique name (see key properties).
Methods are the behaviors of the class, for example, the OperatingSystem class has a Reboot
method and a printer has an EnableDevice method to put it online. However, not all classes have
methods.
An intrinsic method models a CIM operation. Standard intrinsic methods (such as
enumerateInstances, getInstance, modifyInstance) are relevant to all classes.
An extrinsic method is defined on a CIM Class in some Schema that is unique to that class.
Properties are the attributes of a class. For example, there is a ParticipatingCS association exists
between a CIM_ComputerSystem and a CIM_Cluster. This association has two properties,
RoleOfNode and StateOfNode, to describe attributes of the ComputerSystem as a node within the
Cluster.
Key properties (one or more properties defined with a “key” qualifier) are identifiers. Keys in
classes and subclasses provide a way to uniquely identify the instance that inherits them. All
instances inherit a key, or a set of keys, from their superclass. The value that the instance gives
52 Representation of resources