3. Advantages of Parsing Visual Languages in a General Purpose Graphics Editor
A general purpose editor could be used to construct visual language phrases, giving the user more graphic freedom. But of course the deficiency of general purpose graphics editors is that although we can draw anything we want, there is no specialized help for drawing special purpose things (by definition). Added to this is the fact that when we're finished we can't do anything with the drawing.
Spatial parsing offers a way to cure these deficiencies and obtain special purpose utility from a general purpose graphics editor. Spatial parsing recovers underlying syntactic structure so that a spatial arrangement of visual objects can be interpreted as a phrase in a particular visual language. Interpretation consists of parsing and then semantic processing so that appropriate action can be taken in response to the visual phrase. Appropriate action may include: assistance for agile manual manipulation of objects, compilation into an internal form representing the semantics, translation into another text-graphic language, or simply execution as an instruction to the computer.
Previous work [Lakin86a] has shown that structuring the elements in the phrase is the difficult part. Once a parse tree has been constructed, then semantic processing -- at least for the formal visual languages considered in this paper -- is relatively straight-forward. And so through spatial parsing the user can have semantic processing of visual phrases, and thus the advantages of employing a general purpose graphics editor as a visual language interface. First the user simply creates some text and graphics, and then later has the system process those objects as a visual expression under a particular system of interpretation. By selecting the system of interpretation and when it is to be applied, the user gets flexibility (similar to the flexible interaction between text editing and interpreptation/compilation in emacs-based LISP programming environments, [Stallman81]). In fact, different visual languages can even be used in the same image, blackboard-style.