The family of A x Grammars

This note describes the rationale behind AAx Grammars. AAx Grammars are a class of two-level grammars, Context-Free grammars extended with features and operations. Originally invented for the description of natural languages, various forms of AAx Grammars have found numerous applications in Computer Science, and eecient implementations were made. In the last years AAx Grammars with set-valued attributes (agfl) have found succesfull applications as a \lean formal-ism" for describing the surface syntax of natural languages. Readers who have some experience in the use of AAx Grammars may nd in this note the necessary background to place this experience into perspective.