HP WBEM Services Software Developer's Kit for HP-UX Provider and Client Developer's Guide A.01

Provider Implementation

Provider Design Considerations

Chapter 464

is built (PG_ProviderModule.Location), and the schema element with

which it is associated (PG_ProviderCapabilities.ClassName).

However, for clarity, it is useful to choose names that help to identify the

element. The conventions evident in the previous example show how this

may be done.

Key Values: Uniquely Specifying an Instance

Most providers manipulate instances or instance references (also called

object paths) in some way. The set of all keys of an instance deﬁnes the

unique identity of an instance within a namespace of managed objects.

For example, there are possibly many users whose Name is "smith", but

on any given UNIX computer system, there can be only one called

"smith." In order to know exactly which user "smith" we are interested in

(to address email, for example), we must know the name of the system in

question. Therefore, for a user account, a unique identiﬁcation must

include the SystemName as well as the Name (just as an Internet email

address is speciﬁed as username@domain-name). In this example of a

class representing a user account, the SystemName and Name, together,

form a set of key properties that uniquely deﬁne each instance. In this

example, the SystemName is said to specify the context (or scope) in

which the Name will be unique. For many classes in the CIM model in

which keys are deﬁned, there will be at least one key property to specify

the scope of the class's other keys.

Keys that specify necessary scope are always propagated from another

class of object, as mentioned in the section on Common Properties in

Chapter 3, under General Schema Use Cases. The SystemName key

present in many CIM classes is propagated from the Name property of the

CIM_System class (or one of its subclasses). When scoping keys exist in a

class deﬁnition, the classes from which the scoping keys are propagated

are also speciﬁed as key properties. So if there is a SystemName key,

there must be a property specifying the name of the class from which the

SystemName is obtained. This key is the SystemCreationClassName.For

a typical class in the hierarchy of CIM_ManagedSystemElement,

(CIM_LogicalDevice, for example), the full set of key properties might

be:

• SystemCreationClassName

The name of the class which has an instance from which the value of

the SystemName property is obtained. This could be, for example,

CIM_ComputerSystem.