Subgrammars, Rule Classes and Control in the Rosetta Translation System

The paper discusses a recent extension of the linguistic framework of the Rosetta system. The original framework is elegant and has proved its value in practice, but it also has a number of deficiencies, of which the most salient is the impossibility to assign an explicit structure to the grammars. This may cause problems, especially in a situation where large grammars have to be written by a group of people. The newly developed framework enables us to divide a grammar into subgrammars in a linguistically motivated way and to control explicitly the application of rules in a subgrammar. On the other hand it enables us to divide the set of grammar rules into rule classes in such a way that we get hold of the more difficult translation relations. The use of both these divisions naturally leads to a highly modular structure of the system, which helps in controlling its complexity. We will show that these divisions also give insight into a class of difficult translation problems in which there is a mismatch of categories.