Top-down tree transducers with regular look-ahead

Top-down tree transducers with regular look-ahead are introduced. It is shown how these can be decomposed and composed, and how this leads to closure properties of surface sets and tree transformation languages. Particular attention is paid to deterministic tree transducers

Tree adjunct grammars

In this paper, a tree generating system called a tree adjunct grammar is described and its formal properties are studied relating them to the tree generating systems of Brainerd (Information and Control 14 (1969), 217–231) and Rounds (Mathematical Systems Theory 4 (1970), 257–287) and to the recognizable sets and local sets discussed by Thatcher (Journal of Computer and System Sciences 1 (1967), 317–322; 4 (1970), 339–367) and Rounds. Linguistic relevance of these systems has been briefly discussed also

Hypertrees: a study in language specification

A hierarchy of data structures, called the hypertree hierarchy, is presented which has strings and trees as its smallest two elements. A generalized frontiering operation is presented. Grammars, automata and regular expressions are extended to this hierarchy. These are shown to be equivalent and the resulting languages are called regular. This leads to a hierarchy of regular languages on the hypertree hierarchy. These are projected onto the set of strings by the frontier operation resulting in a true hierarchy of string languages. This hierarchy is called the (IO) algebraic language hierarchy. It has regular languages, context free languages and macro languages as its first three levels. It is contained in the set of context sensitive languages but is not equal to it. Other characterizations are presented