Address Space
The DataAccess namespace of the Servers’s address space models the objects and items configured in ACM. When the Server is started, the DataAccess address space is empty. Object nodes and item Data Variable nodes are added as monitored items are requested by the client. This allows the address space to only contain nodes that clients are requesting, rather than modeling the entire SCADA system.
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| Custom Views of the DataAccess namespace is not supported. |
Node Ids and Item Names
The DataAccess namespace is index 2 in the Server. All items requested from ACM must be created in this namespace. All NodeIds in the DataAccess namespace are of type string and have the following format:
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| Object names and Item names in the DataAccess namespace are case sensitive, but within ACM they are not. All connecting client applications should use the same case when defining a monitored item so that multiple nodes are not created in the address space. Example, “myRtu.40001” and “MyRtu.40001” refer to the same item in ACM but will result in two nodes being created in the DataAccess Namespace. Another example is “MyRtu.Demand” and “MyRtu.demand”. |
Browsing
The OPC UA Server supports browsing of the address space by a client application. The browsing functionality is done in a virtual manner because the entire ACM configuration is not modeled in the address space; only the objects and items that have an associated Monitored Item are. As a client browses, objects being browsed, such as folders, devices, and connections, are created in the address space if they do not already exist there. Data items associated with those objects can be browsed but are not created in the address space automatically. Item nodes are only created when a Monitored Item for it is requested by a client so at browse time, not all data items in the browse list will exist in the address space.
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| Browsing of custom Views is not supported. |
Monitored Items
Monitored items are used to obtain real time data from the ACM system by OPC UA clients. Nodes representing ACM items do not exist in the DataAccess namespace until a client requests a monitored item for it.
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