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Data is hierarchically organized in trees of nodes and items where the items are the leafs. The nodes in the hierarchy have
a type (for example, substation, pump, breaker, or any collection of items). The type is transparent to the interface. An
item is an instance of a property belonging to a type. Properties can describe any kind of state variables, control variables,
or parameters existing in a control system.
Data transferred by reads or callbacks are time stamped and quality coded.