Computers are increasingly being seen not only as computing tools but more so as communication tools, thus placing special emphasis on human-computer interaction (HCI). In this article, the focus is on visual HCI, where the messages exchanged between human and computer are images appearing on the computer screen, as usual in current popular user interfaces. We formalize interactive sessions of a human-computer dialogue as a structured set of legal visual sentences, i.e., as a visual language, and show how rewriting systems can be generalized to specify both the pictorial and the computational aspects of visual languages. To this end, Visual Conditional Attributed Rewriting (VCARW) systems are introduced, and used for specification of visual languages. These specifications are given as inputs to a procedure illustrated in the article as a system of algorithms, which automatically generates control mechanisms of the interaction, thus favoring the design of more reliable and usable systems.

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Abstract:Context: Patterns are used in different disciplines as a way to record expert knowledge for problem solv-ing in specific areas. Their systematic use in Software Engineering promotes quality, standardization, reusability and maintainability of software artefacts. The full realisation of their power is however hindered by the lack of a standard formalization of the notion of pattern. Objective: Our goal is to provide a language-independent formalization of the notion of pattern, so that it allows its application to different modelling languages and tools, as well as generic methods to enable pattern discovery, instantiation, composition, and conflict analysis. Method: For this purpose, we present a new visual and formal, language-independent approach to the specification of patterns. The approach is formulated in a general way, based on graphs and category theory, and allows the specification of patterns in terms of (nested) variable submodels, constraints on their allowed variance, and inter-pattern synchronization across several diagrams (e.g. class and sequence dia-grams for UML design patterns). Results: We provide a formal notion of pattern satisfaction by models and propose mechanisms to sug-gest model transformations so that models become consistent with the patterns. We define methods for pattern composition, and conflict analysis. We illustrate our proposal on UML design patterns, and discuss its generality and applicability on different types of patterns, e.g. workflow patterns, enterprise inte-gration patterns and interaction patterns. Conclusion: The approach has proven to be powerful enough to formalize patterns from different domains, providing methods to analyse conflicts and dependencies that usually are expressed only in tex-tual form. Its language independence makes it suitable for integration in meta-modelling tools and for use in Model-Driven Engineering.

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