Editing Feature interaction problem (section)

==Example==
In the context of [[telephony]], a [[telephone line]] (the system) typically offers a set of features that include [[call forwarding]] and [[call waiting]].  Call waiting allows one call to be suspended while a second call is answered, while call forwarding enables a customer to specify a secondary phone number to which additional calls will be forwarded in the event that the customer is already using the phone.

To illustrate the example, we consider a telephone line provided to a customer, and we assume that both call forwarding and call waiting are enabled on the line. When a first call arrives on the line, the phone rings and is answered.  Since neither feature is activated by the first call, there is no noticeable problem.  When a second call arrives before the first has terminated, the telephone system has a decision to make: whether the call should be forwarded to the secondary number (call forwarding) or the person who answered the first call should be notified that another call has arrived (call waiting).  Since this decision has no obvious correct answer, the optimal answer depends on the needs of the customer.  This ''feature interaction'' is a specific example of a general and common problem that has become prevalent due to increasing system complexity.

In this situation, it is possible that the system’s decision will be made in a [[Nondeterministic algorithm|non-deterministic]] fashion due to [[Concurrency (computer science)|race conditions]] and other design factors.  The consequences of feature interactions can range from minor irritations to life-threatening software failures, and therefore there is ongoing research that aims to find ways of ''detecting'' as well as ''resolving'' feature interactions.