Open APIs

Hello, 

I have a question regarding to the quantity object which is inside the adjustProductStockItem of the adjustProductStock endpoint (POST). 

Is the amount of the Quantity object meant as an absolute or relative value ? If it is an absolute value there has to be an check about the current quantity in stock and then setting this to amount x. But what if between the check and the adjustment was a request from another system and the amount is not correct anymore ? I don't understand how this could work with different systems asynchronously adjusting the stock quantity. 

My second thought was that these quantities could be relative so if the amount of the Quantity object is 5 then there will be added 5 to the actual ProductStock. By setting the quantity to negative the amount will be subtracted from the ProductStock. I don't know if that is a solution for the problem or if I'm getting anything wrong with the adjustment endpoint. I would be glad if someone could clarify this topic.

Thanks in advance !