Additionally, an adaptive architecture would be one that is modular so that layers of the infrastructure build on each other. As Figure 2 shows, we could achieve this through separation of business services, application, and infrastructure layers.

With this kind of architecture, we can apply WSDM in the interactions between the services and the management control points. Furthermore, we can use WSDM to virtualize up the stack from infrastructure to application to business services. The end result is a more modular, standardized approach to managing IT. With WSDM, an IT organization can begin to more easily drive change from the business down to IT.

The WSDM Technology Stack
WSDM MUWS outlines several interfaces that can be defined for a resource (see Table 1). We refer to these interfaces as Manageability Capabilities. There are capabilities for resource identity, as well as resource correlation to assert uniqueness among resources. Additional capabilities exist for describing relationships among resources and for receiving notifications when resources get created. These capabilities offer a consumer the ability to discover and relate deployed applications and services.

Given a set of discovered resources, a consumer would need to be able to manage and monitor it. MUWS defines capabilities for gathering performance metrics and statistics, as well as interfaces for configuring a resource. Operations are exposed for defining the state model for a resource and for querying its operational status.

To better understand how these capabilities are addressed, let's examine the specifications upon which WSDM depends. As Figure 3 shows, WSDM MUWS builds on two additional sets of specifications: WS-Resource Framework (WS-RF) and WS-Notifications (WS-N). WS-RF provides a set of mechanisms for accessing stateful resources exposed via Web services. WS-RF uses WS-Addressing to provide Web services endpoints for stateful resources. WS-RF also defines the WS-ResourceProperties specification, which defines a way to represent, advertise, and access the properties that a stateful resource exposes.

The WS-N family of specifications defines a notification model for Web services. As part of this model, WS-N includes the WS-BaseNotification specification. This specification defines the set of messages used to implement a publish-subscribe interaction model for Web services. Additionally, WS-N includes the WS-Topics specification, used to represent and characterize items of interest for notifications. Implementations of WSDM MUWS would leverage WS-BaseNotification, WS-Topics, and WS-ResourceProperties, along with a number of core Web services specifications (XML-S, SOAP, WSDL, etc.)

A Closer Look Inside WSDM MUWS
Let's now take a closer look at how WSDM can be used to manage an IT resource. We'll specifically look at resource properties, state and metrics, events and notifications, and resource discovery.

Resource Properties
It's a common requirement to retrieve properties for a manageable resource or to locate a specific resource that matches a given set of criteria. WS-ResourceProperties is the key specification that would be used to read and write properties for a stateful resource. For example, management of a disk drive might require exposing certain characteristics, such as the number of blocks and the block size for the device. This could be modeled in XML as follows:

<GenericDiskDriveProp xmlns:tns="http://disk.com/diskDrive" >
   <tns:NumberOfBlocks>22</tns:NumberOfBlocks>
   <tns:BlockSize>1024</tns:BlockSize>
</GenericDiskDriveProp>

A consumer that needs to retrieve this property could use the GetResourceProperty operation as follows:

<wsrp:GetResourceProperty xmlns:dd="http://disk.com/diskDrive" >
   dd:BlockSize
</wsrp:GetResourceProperty>

A consumer could also use the QueryResourceProperties operation to locate a disk drive that had more than 20 1K blocks:

<wsrp:QueryResourceProperties>
   <wsrp:QueryExpression>
boolean(/*/NumberOfBlocks > 20 and /*/BlockSize=1024)
   </wsrp:QueryExpression>
</wsrp:QueryResourceProperties>

State and Metrics
State and metrics are also important for controlling the operational state and determining the overall health of a resource. The WSDM State Capability offers a framework for defining a state model for a resource. A defined model makes it easy to represent transitions between states and to control a resource's behavior. Figure 4 shows a very simple state model that could be created for a given resource.

Additionally, StateCapability Topics can be used for sending events when a resource state changes. In this manner, a management system can automatically determine whether a resource is in a healthy, active state.

MUWS metrics can also be useful in monitoring the overall performance and health of a resource. These metrics, represented by a number of different data types, can be collected for a resource at defined time intervals. MUWS provides attributes such as ResetAt, LastUpdated, and Duration for managing the metric collection process. There is also a CurrentTime resource property, which can be used for time synchronization during data collection.