 Since the 1970s, there has been a gradual trend away from purely procedural approaches to ones aimed at encoding the bulk of linguistic and world knowledge in more understandable, modular, re-usable forms, with firmer theoretical foundations. This trend was enabled by the emergence of comprehensive syntactico-semantic frameworks such as Generalized Phrase Structure Grammar (GPSG), Head-driven Phrase Structure Grammar (HPSG), Lexical-Functional Grammar (LFG), Tree-Adjoining Grammar (TAG), and Combinatory Categorial Grammar (CCG), where in each case close theoretical attention was paid both to the computational tractability of parsing, and the mapping from syntax to semantics. Among the most important developments in the latter area were Richard Montague's profound insights into the logical (especially intensional) semantics of language, and Hans Kamp's and Irene Heim's development of Discourse Representation Theory (DRT), offering a systematic, semantically formal account of anaphora in language. 