View a Summary of a Client Object

To view a summary of the characteristics of the opcda object you created, enter the variable name you assigned to the object at the command prompt. For example, this is the summary for the object da.

da

The items in this list correspond to the numbered elements in the object summary:

Get the DA Server Name Space

You use the getnamespace function to retrieve the name space from an OPC server. You must specify the client object that is connected to the server you are interested in. The name space is returned to you as a structure array containing information about each node in the name space.

The example below retrieves the name space of the Matrikon OPC Simulation Server installed on the local host.

da = opcda('localhost','Matrikon.OPC.Simulation.1');
connect(da);
ns = getnamespace(da)

ns = 
3x1 struct array with fields:
    Name
    FullyQualifiedID
    NodeType
    Nodes

The fields of the structure are described in the following table.

From the example above, exploring the name space shows.

ns(1)

ans = 
                Name: 'Simulation Items'
    FullyQualifiedID: 'Simulation Items'
            NodeType: 'branch'
               Nodes: [8x1 struct]

ns(3)

ans = 
                Name: 'Clients'
    FullyQualifiedID: 'Clients'
            NodeType: 'leaf'
               Nodes: []

From the information above, the first node is a branch node called 'Simulation Items'. Since it is a branch node, it is most likely not a valid server item. The third node is a leaf node (containing no other nodes) with a fully qualified ID of 'Clients'. Since this node is a leaf node, it is most likely a server item that can be monitored by creating an item object.

To examine the nodes further down the tree, you need to reference the Nodes field of a branch node. For example, the first node contained within the 'Simulation Items' node is obtained as follows.

ns(1).Nodes(1)

ans = 
                Name: 'Bucket Brigade'
    FullyQualifiedID: 'Bucket Brigade.'
            NodeType: 'branch'
               Nodes: [14x1 struct]

The returned result shows that the first node of 'Simulation Items' is a branch node named 'Bucket Brigade', and contains 14 nodes.

ns(1).Nodes(1).Nodes(9)

ans = 
                Name: 'Real8'
    FullyQualifiedID: 'Bucket Brigade.Real8'
            NodeType: 'leaf'
               Nodes: []

The ninth node in 'Bucket Brigade' is named 'Real8' and has a fully qualified ID of 'Bucket Brigade.Real8'. You use the fully qualified ID to refer to that specific node in the server name space when creating items.

You can use the flatnamespace function to flatten a hierarchical name space.

Get Information about a Specific Server Item

In addition to publishing a name space to all clients, an OPC server provides information about the properties of each of the server items in the name space. These properties provide information on the data format used by the server to store the server item value, a description of the server item, and additional properties configured when the server item was created. The additional properties can include information on the range of the server item, the maximum rate at which the server can update that server item value, etc. See OPC DA Server Item Properties.

You access a property using a defined set of property IDs. A property ID is simply a number that defines a specific property of the server item. Property IDs are divided into three categories:

You query properties of a server item using the serveritemprops function, specifying the client object, the fully qualified item ID of the server item you are interested in, and an optional vector of property IDs that you want to retrieve. If you do not specify the property IDs, all properties defined for that server item are returned.

The following example queries the Item Description property (ID 101) of the server item 'Bucket Brigade.ArrayOfReal8' from the example in Get the DA Server Name Space.

p = serveritemprops(da, 'Bucket Brigade.ArrayOfReal8', 101)

p = 
             PropID: 101
    PropDescription: 'Item Description'
          PropValue: 'Bucket brigade item.'

For a list of OPC Foundation property IDs, see OPC DA Server Item Properties.