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26.2 WMI ArchitectureThe WMI architecture is composed of two primary layers: the CIM infrastructure, which includes the CIMOM and CIM Repository, and the WMI providers. While the concepts Microsoft uses are very similar to the WBEM/CIM standards, they did not implement one very important component: the use of web technologies for the transport mechanism. Instead of using HTTP to transport messages between the WMI infrastructure and clients, Microsoft uses COM and DCOM, two Microsoft-specific technologies. This limits the use of WMI to only Microsoft platforms. That being said, the capabilities to manage Microsoft-based platforms with WMI are nearly unlimited. More and more vendors are utilizing WMI not only to manage components of the Microsoft OS but also to manage their own applications. NMicrosoft has also become heavily invested in WMI by providing WMI providers for nearly all of its major applications, including Active Directory, Exchange 2000, DNS, and even Microsoft Office. 26.2.1 CIMOM and CIM RepositoryThe CIM Repository is the primary warehouse for management data. It contains the static data that does not change very frequently, such as memory or disk size. The CIMOM or CIM Object Manager handles requests from clients, retrieves data from the CIM Repository, and returns it to the client. The CIMOM also provides an event service, so that clients can register for events and be notified dynamically when they occur. For dynamic data, such as performance monitor counters, the CIMOM will interact directly with a WMI provider instead of retrieving the data directly from the CIM Repository. The CIM Repository cannot store all possible data that is needed by the various WMI providers. The storage requirements would be significant, not to mention that a lot of the data would become out-of-date almost immediately after it was stored. 26.2.2 WMI ProvidersThe WMI providers contain much of the intelligence behind WMI. Typically a provider will be implemented for each individual managed component, such as the Event Log or Active Directory Trusts. Each provider is responsible for interacting with its managed component and can perform certain functions implemented by methods on classes representing that component. Also, as described earlier, some providers interact with the CIMOM to provide dynamic data that cannot be held in the CIM Repository. Each WMI provider is also associated with a namespace. The namespace is used to segregate where WMI providers store their data and class definitions. Think of it as a file system. You could store all of your files in a single directory, but it would be hard to manage. By storing data and class definitions for providers under different namespaces, you don't have to worry about confusing the EventLog provider with the Active Directory Trust provider. Table 26-1 contains the more commonly used and AD-related WMI providers and the associated namespace.
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