Grammars of natural languages can be expressed as mathematical objects, similar to computer programs. Such a formal presentation of grammars facilitates mathematical reasoning with grammars (and the languages they denote), as well as computational implementation of grammar processors. This book presents one of the most commonly used grammatical formalisms, Unification Grammars, which underlies contemporary linguistic theories such as Lexical-Functional Grammar (LFG) and Head-driven Phrase Structure Grammar (HPSG). The book provides a robust and rigorous exposition of the formalism that is both mathematically well-founded and linguistically motivated. While the material is presented formally, and much of the text is mathematically oriented, a core chapter of the book addresses linguistic applications and the implementation of several linguistic insights in unification grammars. Dozens of examples and numerous exercises (many with solutions) illustrate key points. Graduate students and researchers in both computer science and linguistics will find this book a valuable resource.

The main purpose of this book is to bring together much of the research conducted in recent years in a subject I find both fascinating and impor tant, namely fairness. Much of the reported research is still in the form of technical reports, theses and conference papers, and only a small part has already appeared in the formal scientific journal literature. Fairness is one of those concepts that can intuitively be explained very brieft.y, but bear a lot of consequences, both in theory and the practicality of programming languages. Scientists have traditionally been attracted to studying such concepts. However, a rigorous study of the concept needs a lot of detailed development, evoking much machinery of both mathemat ics and computer science. I am fully aware of the fact that this field of research still lacks matu rity, as does the whole subject of theoretical studies of concurrency and nondeterminism. One symptom of this lack of maturity is the proliferation of models used by the research community to discuss these issues, a variety lacking the invariance property present, for example, in universal formalisms for sequential computing."