Creating Annotation Tools with the Annotation Graph Toolkit
  The Annotation Graph Toolkit is a collection of software supporting the development of annotation tools based on the annotation graph model. The toolkit includes application programming interfaces for manipulating annotation graph data and for importing data from other formats. There are interfaces for the scripting languages Tcl and Python, a database interface, specialized graphical user interfaces for a variety of annotation tasks, and several sample applications. This paper describes all the toolkit components for the benefit of would-be application developers. 
Kazuaki Maeda, Steven Bird, Xiaoyi Ma, and Haejoong Lee