The XML-DA Items category provides status information about the XML-DA tags to which XML-DA clients are subscribed. Status information is shown for XML-DA tags when XML-DA is used to access the database. Each XML-DA tag represents a path to a value for an item.
The status information for each XML-DA tag is categorized as:
- Tag—Indicates the name and location of the XML-DA tag to which the XML-DA client subscribes.
- Subscription—Indicates the name of the subscription being used for retrieving data from the server. You can view status information about the subscriptions on the status display for XML-DA Subscriptions
- Canonical Datatype—Shows the original type of the OPC data that is being requested. This can be:
- VT_BSTR—a string value
- VT_BOOL—a Boolean value
- VT_VARIANT—the type varies (and can be any of the other data types)
- VT_I1—a 1 byte signed integer value
- VT_I2—a 2 byte signed integer value
- VT_I4—a 4 byte signed integer value
- VT_UI1—a 1 byte unsigned integer value
- VT_UI2—a 2 byte unsigned integer value
- VT_UI4—a 4 byte unsigned integer value
- VT_R4—a single precision floating value
- VT_R8—a double precision floating value
- VT_DATE—a date and time value
These datatypes can also be arrays, in which case, the datatype is appended with |VT_ARRAY, for example, VT_UI4|VT_ARRAY.
- Requested Datatype—Shows the data type that has been requested (some OPC clients can request data in a different type to that in which it stored in the ClearSCADA database, for example, a real value could be requested as a string).
The datatypes that can be requested are:
- VT_EMPTY—A value has not been specified. This means that the client has not requested for the value to be converted from its original datatype. The datatype of the value that is returned will be the same as the value’s Canonical Datatype.
- VT_I1—a 1 byte signed integer value
- VT_I2—a 2 byte signed integer value
- VT_I4—a 4 byte signed integer value
- VT_R4—a single precision floating value
- VT_R8—a double precision floating value
- VT_CY—a currency (monetary) value
- VT_DATE—a date and time value
- VT_BSTR—a string value
- VT_BOOL—a Boolean value (True =-1, False=0)
- VT_UI1—a 1 byte unsigned integer value
- VT_UI2—a 2 byte unsigned integer value
- VT_UI4—a 4 byte unsigned integer value.
These datatypes can also be arrays, in which case, the datatype is appended with |VT_ARRAY, for example, VT_UI4|VT_ARRAY.
- Value—Indicates the current value of the OPC tag that corresponds to the value on the Mimic.
- Value Datatype—Shows the type of the OPC data after it has been converted for use. The possible data types are exactly the same as those for Canonical Datatype.
- Quality—Indicates the current quality of the value. This provides an indication as to the reliability of the data.
- Time Stamp—Indicates the time at which the Value and Quality statuses were recorded.