This is an Annotation Graph API for linguistic annotations.
Annotation Graphs are a data structure conceived by Steven Bird and Mark Liberman:
The structure is designed to be a tool-independent way of representing annotated linguistic data, and essentially defines an Annotation Graph as a directed acyclic graph where:
This particular implementation, which is used for LaBB-CAT, developed by the NZILBB, includes extra features that allow tier hierarchies and parent/child constraints to be defined. More details on extra features are available in http://dx.doi.org/10.1016/j.csl.2017.01.004
More API documentation is available here
Apart from use within LaBB-CAT, the object model can be used for other purposes like format conversion, e.g.
More format conversions are available here