3.3 Segment structure.   The smallest element described in phrase structure is the single word, name piece, or morpheme. These compositional atoms are segments. It is helpful to liken them to atoms because they do not show any evidence of further phrasal constituency. They do have a structure however. Segment structure is characterized solely by the presence or absence of attributes, and not by their division into or ordering of any smaller elements.

The first example is a segment represented as a list of features for a given name like “John.” Features may be Boolean (±) or scalar (1,…,n). Each feature is indicated with a plus (+) when present and a minus (–) when explicitly absent. For many segments it may be unspecified, i.e., never used on that segment. Similarly scalar features are present or absent in an ordered way. There is a particular binary feature marked as present on the segment for each value of a scalar feature.

The second example is a segment designating a locality name like “Rome,” the name of cities in present day Georgia, New York, and Italy, as well as of certain other jurisdictions elsewhere in the world and at other times in history.