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Discussion turned into whether the ExchangeItemValueChanged event should be moved to the exchange item, such that you can register for a specific exchange item directly and do not need to register globally and filter out the exchange item that are not relevant. Would be preferable to have in case of distributed computation. But it is a bit more difficult to register in case you want to listen for all ExchangeItemValueChanged events. We move the event to the exchange item 
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Add URI to IDescribable
The right way to add ontology support is most likely to extend the exchange item and the value definition. The URI there by itself does not solve the problem, it is too ambiguous. 
Remove GetHashCode() and Equals() overrides in Backbone package
Similarly, the DescribeSameAs functions are a bit unclear: When does a quantity describe the same as another, which properties should match: description, unit (with description, caption, dimension and conversion factor) or dimension.
Suggestion to make utility functions in the SDK that can do the comparison on the required level and remove the DescribeSameAs methods.
Alternatively, the DescribeSameAs should be precisely documented.
How to make the standard extendable
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