Some proposed properties of dependency structure representation systems:

Rootedness - there is exactly one word W for which the following two statements are both true:

• W is the source of at least one dependency
• W is not the target of any dependency

e.g. for the sentence "John thinks that Mary rocks":

• sbj(thinks,John), sbj(rocks,Mary) is a non-rooted structure
• sbj(thinks,John), obj(thinks,rocks), sbj(rocks,Mary)is a rooted structure

Connectedness - every word is either the source or target of some dependency

nb. rootedness does not entail connectedness and vice versa.

Acyclicity - if there is a sequence of dependencies from W1 to W2, then there is no sequence of dependencies from W2 to W1

Unique headedness - Every word which is the target of some dependency, is the target of exactly one dependency.

Functionality - for each word W and each dependency label T, there is no more than one dependency from W labelled with T

-- MarkMcConville - 14 Aug 2008