The first of the Access Type specification parts, Part 8 – Data Access has been released.  The remaining Access specs are due out in November.   

For those of you who’ve read Part 1 – Concepts, here is the Readers Digest version of how the Data Access specification fits into the picture.  As with all the Access Type specifications, Part 8 outlines how the Core specs (Parts 1-7) are applied, by defining specific Attributes, ObjectTypes, References, etc.  It does not modify anything from the Core or add new interfaces, but rather outlines specific usage of the Core Services. 

As you would expect, Part 8 – Data Access will make extensive use of the MonitoredItem and Subscription Service sets, these being the ‘report by exception’ type interfaces for real time data. In terms of the UA AddressSpace, Part 8 offers a richer information model that allows better distinction between typical automation data types such as analog and digital state items.   This also includes improved handling of the Engineering Units and Deadbanding.  These were two typical complaints of the existing OPC DA specification. 

If you want the real gory details then you need to join the club to get ‘em. (Tom’s done a good job of outlining the reasons why.)