Sequence Diagrams (SDs) are one of the most popular elements of the UML notation to model the dynamics of systems. However, the graphical representation of basic SDs suffers from an inherent ambiguity that has led to different definitions in UML 1.x and in UML 2.0. This ambiguity paves the way for the consideration of several semantics for basic SDs. The paper studies four of these semantics and shows to what extent their differences for a given SD (that is the amount of ambiguity of this diagram) comes from its structural properties (linearity, local control and local causality). The fulfilment of these properties can serve as a measure of the ambiguity of a SD, and thus the attention to be paid at its validation.
In computer-based crisis management, participating actors have to put in common their information systems (IS). One of the main issues they have to face is to interoperate and coordinate these ISs in order to ease their collaborations and take the right decisions at the right moment. For that, they have to set up a Collaborative Information System (CIS) for orchestrating a Collaborative Process (CP) whose activities are performed by the participating ISs. The aim of this paper is to define the functional requirements of such a CIS and then to propose a conceptual architecture meeting these requirements. This architecture supports a perception-decision-action iteration for crisis reduction. Indeed, it provides means to capture information about the impacted real world, to support the definition and the adaptation of the CP managing the crisis reduction, and to coordinate and assign to each participant the actions to be undertaken. These actions modify the real world and lead to perform a new iteration until the crisis resolution.
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