The purpose of subclause 5.4 is to detail the requirements and behaviour for OPC UA Servers supporting Aggregates. The intent is to standardize the Aggregates so users can reliably predict the results of an Aggregate computation and understand its meaning. If users require custom functionality in the Aggregates, those Aggregates should be written as custom vendor defined Aggregates.
The standard Aggregates shall be as consistent as possible, meaning that each Aggregate’s behaviour shall be similar to every other Aggregate’s behaviour where input parameters, Raw data, and boundary conditions are similar. Where possible, the Aggregates should deal with input and preconditions in a similar manner.
Subclause 5.4 is divided up into two parts. Subclause 5.4.2 deals with Aggregate characteristics and behaviour that are common to all Aggregates. Subclause 5.4.3 deals with the characteristics and behaviour of Aggregates that are aggregate-specific.