Non-local Choice and Implied Scenarios

A number of issues, such as non-local choice and implied scenarios, that arise in Message Sequence Charts (MSCs) have been investigated in the past. However, existing research on these two issues show disagreements regarding how they are related. In this paper, we analyse the relations among existing conditions for non-local choice free and Closure Conditions (CCs) for implied scenarios. On the basis of this, we propose a new definition for non-local choice and a non-local choice free condition derived from CCs of implied scenarios. Compared to existing conditions, we argue that the new condition covers more non-local choices that satisfy the informal idea of non-local choice. We formally show that the existence of non-local choices in an MSC specification results in implied scenarios and the appearance of implied scenarios according to corresponding CCs means there are non-local choices in the specification.