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In DAIS RWOs are represented by Nodes. Property instances at a node are represented by Items. An item may represent a measurement
value, a control output value, or any parameter (for example, a limit value, a unit, a name, a description). A Type and properties
belonging to a type represent an RWO type by DAISProperties. Nodes are hierarchically structured and the leafs are Items.
This is shown
in Figure 4-1.
Figure 4-1 DAIS data access server information model
The Component class inherited by the Node and Item classes models the hierarchical structure. The Node may contain any number
of Components as described by the Contains role having the cardinality many (role is a UML concept, refer to [9] for an explanation).
A Component is a member of one Node as described by the MemberOf role having the cardinality of 1. A Component can be both
a Node and an Item through the inheritance, which means a Node can contain other Nodes or Items. An Item cannot contain any
Components as it only inherits the MemberOf role and not the Contains role.