The second of the Access Type specification parts, Part 11- Historical Access has been set to Release Candidate.  The remaining Access specs are still targeting the end of November.

I’m continuing my Readers Digest version of how the Access specifications fit into the overall OPC UA picture.  (You should at least read Part 1 – Concepts for this to have any context).  As with all the Access Type specifications, Part 11 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.

First thing you might notice, is this part is called Historical Access (not Historical Data Access).  The name change reflects the fact that Part 11 includes historical data access and historical event access.  A standardized method for accessing event based history, rather that pure time series data has been something people have been wanting for some time.  The history services, HistoryRead and HistoryUpdate are part of the base specifications, so  Part 11 outlines the specifics as they apply to typical time-series data, and event based history.  Part 11 leverages the richer information model that OPC UA provides and now allows any object, property, node or view to expose history.  Pretty much everything from the COM based HDA specification has made it into Part 11.  The functionality of Read Raw, Read At Time, Read Modified, Insert, Replace, Insert/Replace, and Read Processed with the standard aggregates is all in there, but in a much more streamlined and integrated format.   The HDA Quality information has been incorporated into the standard Status Codes, which makes life much easier.   We did take this opportunity to trim some deadwood.  Stuff that didn’t make the cut includes Playback, Advice functions, String-based Relative timestamps and the Statistical Aggregates (the ‘standard’ aggregates were vendor defined anyway).

Members can get the juicy details of the specifications from the downloads section.   Part 11 should make it to full Release by the end of the month, so if you got somethin’ to say about history, get your comments in now.