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A property represents a characteristic of a node that can be described with a value. A given property may apply to many nodes,
for each such node there will be an item
corresponding to the property. (See Section 4.2.4, “DAISItem IDL,? on page 4-15).
A DAIS property corresponds to a property in RDF and the DAF. A DAIS property corresponds to the concept of a property in
OPC accessed with the IOPCItemProperties::QueryAvailableProperties() method. However, the six core OPC properties (timestamp,
quality, value) do not correspond to properties in DAIS. They are given special treatment in OPC (they are not the same as
other OPC properties). See
Section 4.2.4, “DAISItem IDL,? on page 4-15 for interfaces to handle these.
Each property is identified by a ResourceID and has a label, description, and canonical data type. The canonical data type
is a member of the SimpleType enumeration and indicates the preferred CORBA atomic data type for values of this property.
Every item of a given property has an identical canonical data type. A property may be obtained for any item via the property
member of the ItemID. All properties that apply to a given node may be obtained, given the node’s ResourceID. All properties
that apply to the nodes of a given type may be obtained, given the TypeID. A property may be represented as a node in one
or more of views provided by a DAIS server. In this case the node’s ResourceID and the property’s ResourceID are identical.
The property’s parent is always the node representing the type to which it belongs. The property’s label is identical to the
node label and the property’s description is identical to the node description.
The property IDL defines a main interface DAIS::Property::IHome for browsing properties. The information model describing
how the properties are related to nodes and items is found
in Section 4.1.1, “Nodes, Items, Types, and Properties,? on page 4-2
.
Figure 3-4 DAIS property IDL in UML