Annotation processes for flexible management of contextual information

We propose the use of annotations as a way to flexibly enrich a domain of interest with information concerning different contexts of use for its elements. We provide a formal model of annotation in the framework of typed graphs, in which the presence of annotations is reified through nodes and edges of specific types, relating nodes from different domains. This allows the flexible activation and de-activation of annotations, as well as the addition of several annotations from different domains on the same element. We show that annotations give rise to a category, where pushouts are the basic construct for the composition of annotation-related processes. We prove some properties of annotated graphs and discuss examples drawn from several fields.