As stated in Chapter 1, the goal of the methods developed in this thesis is to improve the parsing times for TFSGs, by means of indexing. At the moment of writing this thesis, the available literature on this topic is rather scarce. Most of the currently used techniques for improving TFSG parsing times use no indexing, or employ filtering as a substitute for true indexing. Other directions of research in this domain address other weaknesses of TFSG parsing, such as the inefficient encoding of typed feature structures, the parsing algorithm, or the lack of a suitable programming environment. This section presents a short overview of efforts directed at improving TFSG parsing times by means of filtering, which is the closest related technique to indexing.