  Semantic relations are often signaled with prepositional or possessive
marking--but extreme polysemy bedevils their analysis and automatic
interpretation. We introduce a new annotation scheme, corpus, and task for the
disambiguation of prepositions and possessives in English. Unlike previous
approaches, our annotations are comprehensive with respect to types and tokens
of these markers; use broadly applicable supersense classes rather than
fine-grained dictionary definitions; unite prepositions and possessives under
the same class inventory; and distinguish between a marker's lexical
contribution and the role it marks in the context of a predicate or scene.
Strong interannotator agreement rates, as well as encouraging disambiguation
results with established supervised methods, speak to the viability of the
scheme and task.
