A lesson in SOA model-based mgmt.

WS-RT specification lets users manage complex model systems.

By William Vambenepe , Network World , 02/09/2007

This vendor-written tech primer has been edited by Network World to eliminate product promotion, but readers should note it will likely favor the submitter's approach.

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IT practitioners striving to meet changing business needs are using service-oriented architectures to speed development, improve visibility into the business impact of IT events, and lower integration and management costs.

To reap these benefits, IT staffs need to provide some level of semantic integration between IT systems. Semantic integration means that not only do systems need to connect (that is, be able to exchange messages), they also need to have a common language for these messages to be translated into action in an automatic way. Without this shared understanding, messages are exchanged but must be translated by a human operator before resulting in any action.

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Semantic integration is achieved via models that contain a description of the elements composing a system, as well as the relationships linking them. While not a cure for all problems, models allow better semantic integration through sharing of model elements and the use of transformations, policies and desired-state type of information.

Models can be easily translated from one modeling language to another, so the invoker of the model and the service providers don't need to use the same modeling language. Service Modeling Language, for example, was designed for that purpose. The sharing of models across the life cycle of the system allows experts to enrich the model with information relevant to each stage of the life cycle (such as design, implementation, testing, deployment, operation and retirement).

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One possible application of WS-RT

1	A user describes the system to create (such as provisioning a Windows 2003 server) by selecting from a library of existing IT models, then sends a WS-RT Create message to the Windows 2003 server-provisioning tool defined in that model.
2	The provisioning tool creates/configures/discovers the resources needed (in this case, perhaps a VMware image of Windows 2003 to be deployed on a server).
3	The provisioning tool returns Endpoint Reference, XML code that lets Web services messages be sent a destination for the system created (the Windows 2003 server).
4	Later configuration changes are done by updating the model using a WS-RT Put message. The provisioning tool reconfigures the system and returns a success code, confirming the reconfiguration.

Click to see: Possible application of WS-RT

WS-ResourceTransfer (WS-RT) plays at the intersection of SOA and model-based management. While its goals are modest and its usage will often be hidden, it meets a critical need in allowing model-driven interactions to be conducted in an SOA.

WS-RT defines a set of Simple Object Access Protocol messages that are used to provide flexible access to a model-driven service. It is fully compliant with the WS-Transfer specification (a World Wide Web Consortium submission that is one of the components of WS-Management) on which it is based.

But while WS-Transfer allows access to the entire representation of the model of a system that is being accessed (in order to read, update, create or destroy it), WS-RT lets individual parts be specified. This capability is useful when interacting with models of individual resources (such as a server) and is critical in interacting with large models that represent complex systems (such as a data center), in which case interacting with the entire model is impractical.