Given a root system $\Delta$ a choice of **positive/negative roots** is a decomposition of the elements of $\Delta$ into two subsets $\Delta^+$ and $\Delta^-$ satisfying 

>  $~~~ \Delta^+ = - \Delta^-    ~~~~~~~~(*)$

and such that for any two roots $\alpha,\beta \in \Delta^+$ such that $\alpha + \beta \in \Delta$ it holds that 

> $\alpha + \beta \in \Delta^+$.

Is there a name for a decomposition into subsets $\Delta^+$ and $\Delta^-$ that only satisfy (*)? 

Do such decompositions arise naturally in the study of, or applications of, root systems?