Abstract.
We present the formal specification and verification of a lip-synchronisation protocol using the real-time model checker Uppaal. A number of specifications of this protocol can be found in the literature, but this is the first automatic verification. We take a published specification of the protocol, code it up in the Uppaal timed automata notation and then verify whether the protocol satisfies the key properties of jitter and skew. The verification reveals some aws in the protocol. In particular, it shows that for certain sound and video streams the protocol can time-lock before reaching a prescribed error state. We also discuss our experience with Uppaal, with particular reference to modelling timeouts and to deadlock analysis.
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The latest developments in human computer interfaces aim at greater ease of use, and the exploitation of human communication and interaction skills typical of non-computerised environments. This kind of interaction is continuous rather than purely discrete. Continuous interaction implies a tighter coupling between system and user, and raises complicated synchronisation issues where real-time requirements and intrinsic variation of human behaviour play an essential role. In this paper, we propose a human centred layered reference model to reduce the design complexity of systems exhibiting continuous interaction. In the context of the layered model, we discuss the role that formal modelling can play in the design of these systems.
Abstract.
We argue that cognitive models should be used in analysing the usability of multi-modal human computer interfaces and further, that formal methods can be advantageously applied to such analysis. In pursuing this objective we specify the Interacting Cognitive Subsystems model formally using the process calculus LOTOS and then we verify that it satisfies certain behavioural goals formulated in the interval temporal logic Mexitl.
This paper presents an approach for investigating in a predictive way potential disruptive effects of interruptions on task performance in a multitasking environment. The approach combines previous work in the field of interruption analysis, formal description techniques for interactive systems and stochastic processes to support performance analysis of user activities constrained by the occurrence of interruptions. The approach uses formal description techniques to provide a precise description of user tasks, and both system and interruptions behavior. The detailed mechanism by which systems and interruptions behave is first described using a Petri nets-based formal description technique called Interactive Cooperative Objects (ICO). The use of a formal modeling technique for the description of these three components makes it possible to compare and analyze different interaction techniques. In particular, it allows us to determine which of the system states are most affected by the occurrence of interruptions. Once composed together, models describing the system, user tasks and interruptions behavior are transformed into PEPA models (i.e. Performance Evaluation Process Algebra) that are amenable to performance analysis using the PRISM model checker. The approach is exemplified by a simple example that models two interaction techniques for manipulating icons in a desktop environment.
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