  The Annotation Graph Toolkit (AGTK) is a collection of software which
facilitates development of linguistic annotation tools. AGTK provides a
database interface which allows applications to use a database server for
persistent storage. This paper discusses various modes of collaborative
annotation and how they can be supported with tools built using AGTK and its
database interface. We describe the relational database schema and API, and
describe a version of the TableTrans tool which supports collaborative
annotation. The remainder of the paper discusses a high-level query language
for annotation graphs, along with optimizations, in support of expressive and
efficient access to the annotations held on a large central server. The paper
demonstrates that it is straightforward to support a variety of different
levels of collaborative annotation with existing AGTK-based tools, with a
minimum of additional programming effort.
