OPC XML-DA 1.01 Specification Errata

[Jim Luth]

This thread will contain corrections and clarifications to the OPC XML-DA 1.01 Specification found after its publication.

[Jim Luth]

On page 65, the description for RItemList states:
"If ReturnValuesOnReply is "false" and no errors are found, RItemList will be empty."

This statement is not always true. The following logic must be used to determine if RItemList is empty:

RItemList must contain an entry for each item in the SubsribeRequest, in the order of the items in the request, if any of the following conditions are true for one or more items in the request:

1) ReturnValuesOnReply is "true" and the server has a value for the item.
2) The RevisedSamplingRate for the item does not equal the RequestedSamplingRate (or the RequestedSamplingRate was missing).
3) The item has a ResultID that is not S_OK.

If ReturnValuesOnReply is "true" and an item appears in the RItemList with a missing value element, then the Quality must be set to
badWaitingForInitialData. If ReturnValuesOnReply is "false" then the Quality element must be missing.

Note that the RequestOptions do not affect whether items will appear in the RItemList, only what data will appear for the item.

The Timestamp attribute is only present when the value element is present and RequestOptions.ReturnItemTime is "true".

In the comments section on page 65, the following is stated:

'If all items are rejected the server will still return Item elements with the error codes. However, no subscription will be created
and an empty string will be returned as "ServerSubHandle". '

this should read:

'If all items are rejected the server will still return Item elements with the error codes. However, no subscription will be created
and the "ServerSubHandle" must be empty or missing.'

[Jim Luth]

In section 3.1.10 ItemProperty, on page 46, property #108 timeZone is shown as having a data type of unsignedInt. The data type should be Int since the time zone difference could be positive or negative from UTC.