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In OPC data is generally organized in hierarchical structures. In data access the leafs are called leaf nodes and the branches
branch nodes or items. A leaf node or item is the same as an instance of property at an object. A branch node corresponds
to an:
• Object having properties.
• Arbitrary organization of other branch nodes.
• Object having both properties and other branch nodes as children.
In DAIS data access the branch nodes are called nodes and the leaf nodes are called items. In DAIS alarms & events, the branch
nodes are called areas and the leaf nodes sources.
In OPC branch and leaf nodes have a name unique among the nodes or items that are children of the same node. A second name
is formed by combining these names from each branch node in the path from the node or leaf to the root. Both names are called
ItemIDs in OPC and the name created by following the path to the root is sometimes called a fully qualified ItemID.
In DAIS the name unique among the child’s to the same node is called label and the name including the labels from all nodes
in the path to the root is called pathname. Both DAIS branch nodes and leaf nodes have both a label and a pathname.
A label is used in the same way as a name but the word label is preferred before the word name as it denotes something that
is atomic; that is, it cannot be further divided.