Picture grammars

In recent years there has been considerable interest in applying the methods of mathematical linguistics to picture generation and description [1]. In this approach, pictures are regarded as combinations of subpictures, which are in turn built up out of still smaller parts, in analogy with the way that sentences can be broken down into phrases and words. Conventionally, however, mathematical linguistics deals with strings (of words, etc.), whereas pictures do not usually have natural representations as strings of subpictures. This suggests that it would be desirable to generalize the tools of mathematical linguistics so as to allow combining parts into wholes by methods more general than string concatenation.