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Type hierarchies are a way of organizing grammatical properties and capture the generalisation of language. The structures inherit the properties of their parent structures thus reflecting the generalisation of linguistic properties.
example type hierarchy
The example type hierarchy shows one way of organizing parts of speech (pos). Pos is a subtype of the 'root element' feat-struc and branches into the elements prep, adj, conj and agr-pos. All these elements are members of the class pos and inherit all properties that would be assign to pos. However, because they differ from one another in all other aspects they are all daughters of the node pos. The types noun, verb and det in contrast have properties in common and are thus grouped under the type agr-pos (agreement part of speech), inheriting all properties from agr-pos.
Feature structures and attribute value matrices
Feature structures present grammatical properties in the form of attributes and their values. The attributes are referenced from the type hierarchy including inherited properties. Feature structures can be nested, where the value of an attribute is another feature structure.
A common and practical way to write feature structures is by "attribute value matrices" (AVMs). They consist of the name of the entity and its attributes and corresponding values, all enclosed by square brackets. Nested feature structures are marked by another set of brackets indicating the nested structure. Values that are shared by attributes inside the AVMs are marked with a tag. Tagging can thus indicate agreement or the propagation of attribute values to parent structures, for example.
The example AVM is a simple description of the article "the". det is of the type word which according to the underlying type hierarchy is a subtype of the type expression. Expression has the properties of of HEAD (the head element of the expression) and VAL (the valance of the expression). The HEAD is itself, det. The valence of det in this simple model simply states that it has no COMPS (complements), it is intransitive, and its requirement for a SPR (specifier) is satisfied because it does not need one. Because det is a subtype of agr-pos it theoretically could have AGR (agreement) properties of the type agr-cat (agreement category), which could be PER and NUM (person, number). Since this is a det it has neither. For more details see SWB (2003).
(images modelled after SWB (2003),p. 84f)