Merging Scenarios

Scenario languages define typical executions of systems. They are used to represent output traces, but also to capture requirements of distributed systems. Even if several dialects exist, all scenario languages are based on a similar idea: they depict systems runs as compositions of partially ordered sets of events. A drawback of scenarios is that the number of participants in a given interaction cannot be parameterized. With a fixed number of objects in an interaction, it is hard to describe behaviors of systems with dynamic architecture. Message Sequence Charts propose instance creation, but this mechanism needs to know a priori the name of instances that will be created. Another drawback of scenarios is that a description of a system is usually defined by a set of scenarios, which represent typical uses of the system under design in a given situation, but comport some redundancies. The intended behavior of a system can be seen as a combination of all these views. So far, no satisfactory merge operator exists. Scenario languages are all equipped with alternative, sequential, or parallel composition, but these operators do not capture the notion of redundancy that may exist between the composed views. A solution proposed is to gather coherently redundant views given as Live Sequence charts [8]. The main idea is to combine scenarios at runtime. LSCs are executed in parallel, and events that can be executed in several views are synchronized when possible. From an initial set of live scenarios, an event is executed, and new scenarios are “triggered” by this event execution. Two scenarios are declared inconsistent if they contradict each other on the order of common events. The main drawback of this approach is that inconsistency between scenarios may not be discovered if the simulations performed do not pass through a faulty configuration. This paper addresses a second approach that consists in the construction of a new model, preferably using the same scenario language, which is the smallest model to contain all the