Structure and Expressiveness of Visual Computer Languages

One of the meanings that can be assigned to the expression Visual Programming Language (VPL) is that of a programming language whose tokens are visual, rather than textual. Despite the linguistic parallel, however, VPL's can hardly challenge their textual counterparts in the construction of even very simple software programs. But Visual Command Languages (VCL's) seem to have nearly overtaken their textual counterparts as a protocol for user-system interaction. Thus, the very nature of software programs and interface commands appear to be differentially suited for visual representation. In this paper, a classification of visual languages is proposed with respect to the dimensions of structural complexity and interactivity. Whereas languages deprived of a cognitively clear conceptual model in the semantic component seem to be necessarily low on the interactive side, languages deprived of formally clear structuring rules in the syntactic component do not. But, the lack of a powerful grammar seems to affect the language's ability to represent adequately the elements involved in even the simplest computer processes. In order to integrate the adequacy of VCL's to a programming environment, an end-user VPL schema is presented, in which visual parametric and syntactic variations of a classical fractal image — the Koch Curve — are assigned perceptually motivated procedural meanings. Although images in this VPL schema are abstract, and not semiotically iconic or indexical as the majority of VCL images, underlying structural regularities seem to accommodate consistently some semantic notions related to data, control and modular abstractions. A global linguistic and semiotic analysis of the proposed VPL schema suggests that there may be important expressive limits to the quality of genuinely visual programming languages. Nevertheless, the limits of successful visual command languages may apparently be extended to incorporate abstractions that are desirable for end-user programming applications.