General Model Requirements

• Keep the structure of a resource's representation as simple as is possible
• Support the ability to represent more than just virtual machines (e.g. physical machines, routers, load balancers etc) using the same model.
• The model should be extendible so that entities within can be extended with additional provider-specific parameters.
• Do not "leak" technology into the representation (e.g. dependence on IPv4 or IPv6).
• Keep the resource representation's hierarchy depth to a minimum.
• Do separate functional attributes from non-functional attributes via grouping/categorisation.
• Representation model should be equal or a super set of the request model;e.g. I request a resource to have 1GB of RAM. When I view its representation after it is provisioned I see that it has the attribute representing 1GB of RAM but also that is has other attributes such as hostname. This allows for the reuse of the model within the provider's infrastructure landscape and promotes a common "language" and reuse.
• Provide multiple renderings of the representation e.g. XML, JSON, CSV, RDF. Where ever possible these renderings should conform to a schema. Wrapping these renderings inside another schema (e.g. SOAP) should be avoid if possible. This reduces complexity by removing additional dependencies. OVF would be an excellent candidate to provide a standardised rendering of resources. It also has an extension mechanism that can be read about the the specification (section 7.3)