XoomXML is declarative rather than procedural in form. What does this mean?
Let's say you want to use Xoom to deploy configuration. If the representation were procedural, Xoom would have to follow the steps, as laid out in the representation, to convert the old configuration to the new.
By contrast, XoomXML is declarative. It shows not a series of steps but a description of configuration in the desired state. When you deploy configuration, Xoom acts as a black box, performing the steps without you having to know what they are. This is obviously far more convenient to use: XoomXML is much easier to read and you don't have to be a specialist to transport configuration.