Feature interactions of livelock type in IN: a detailed example

Feature interactions (FI) occur when two (or more) features-which work properly when individually activated-interfere with one another and cause undesirable abnormality of the system. Consider two features: ring again (RA) and terminating call screening (TCS). RA allows the caller to call again when encountering a busy signal. TCS allows a phone to prohibit certain calls from coming in. Suppose a phone a is in the screening list of another telephone b. When a calls b, it will be screened out. If a activates RA, a will call b again and again but will be screened out every time. This situation is actually a livelock. This paper proposes the use of temporal colored Petri nets (TCP-nets) for specifying system structures and temporal formulas for specifying the functionality of features. FI can be detected by inspecting whether or not the temporal formula is violated when executing some of the firing sequences which realize T-invariants of the colored Petri net