From the description:
The Annotation Ontology is a vocabulary for performing several types of annotation – comment, entities annotation (or semantic tags), textual annotation (classic tags), notes, examples, erratum… – on any kind of electronic document (text, images, audio, tables…) and document parts. AO is not providing any domain ontology but it is fostering the reuse of the existing ones for not breaking the principle of scalability of the Semantic Web.
Anita de Waard mentioned this in her How to Execute the Research Paper.
Interesting work but you have to realize that all ontologies evolve (except for those that aren’t used) and that not everyone uses the same one.
Still, it is the sort of thing you will encounter in topic maps work so you need to be aware of it.