Table-driven and context-sensitive collage languages

In this paper, we introduce the notions of context-sensitive and TOL collage grammars as generalizations of context-free collage grammars. Both kinds of picture generating devices are more powerful than the context-free case. Nevertheless, the sizes of collages in a TOL collage language can be shown to grow at most exponentially. In contrast to this, there are no such bounds for context-sensitive collage languages because suitable pictorial representations of recursively enumerable sets of strings can be generated. On the other hand, it is still a conjecture that TOL collage languages exist which are not context-sensitive.