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
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MarkMcConville - 14 Aug 2008