Constituent Structure - Part 24 | 100 PHRASE STRUCTURE GRAMMARS AND X-BAR The complex AVM structure can also be represented as a feature geometry the notation common in distributed morphology3 see also Gazdar and Pullum 1982 . The feature geometric representation of 13 is given in 14 14 he Category 1 Agreement noun Num 1 Gender Person sg masc 3rd In the feature-geometric representation the attribute or feature is seen to dominate its value. If you can imagine 14 as a mobile hanging from the ceiling then the AVM in 13 is a little like looking at the mobile from the bottom Sag pc . Feature geometries have an interesting property which is also present in AVMs but less obvious they express implicational hierarchies of features. If you look at 14 you will see that if a noun is specified for person 3rd then it follows that it must also have a specification for agreement. The first of these three notations can still be found in the literature today but usually in a fairly informal way. The AVM and feature geometry notations are generally more accepted and as far as I can tell they are simple notational variants of each other. The use of features in Generalized Phrase Structure Grammar Features are one of the main ways that Generalized Phrase Structure Grammar4 Gazdar 1982 Gazdar Klein Pullum and Sag 1985 henceforth GKPS and citations therein extended and constrained the power of phrase structure grammars in a non-transformational way. An underlying theme in GPSG and HPSG 5 LFG and other approaches is unification. The basic idea behind unification is that when two elements come together in a constituency relationship they must be 3 The feature geometry notation is also used in HPSG but usually not for expressing featural descriptions of categories instead the feature geometric notation is used for indicating implicational hierarchies type or inheritance hierarchies . This usage is also implicit in the Distributed Morphology approach but descriptions are not formally distinguished from the .
