Using the local context for the definition and implementation of visual languages

In general, visual languages need to be simple in order to be easily used and understood. As a result, many of them have simple constructs that can be defined by simply describing local constraints on the constituent elements. Based on this assumption, in a previous research, we developed a local context methodology for the specification of the syntax of simple visual languages such as flowcharts, entity-relationship diagrams, use-case diagrams. In this paper, we extend the methodology by defining a new technique for a local context based semantic translation of a visual language. The technique uses XPath-like expressions, called SGPath, together with a data flow model of execution. As for the case of local syntax checks, attributes and rules to calculate them are defined for each element of the language. For a given element in the abstract sentence graph, the SGPath expressions are used to gather values from its neighbors in order to allow the rules to calculate its semantic attributes. The new methodology has been implemented in the tool LoCoMoTiVe and been tested on visual languages such as entity-relationship diagrams, flowcharts, trees.