Linear Extended Annotation Graphs.

Multistructured (M-S) data models were introduced to allow the expression of multilevel, concurrent annotation. However, most models lack either a consistent or an efficient validation mechanism. In a former paper, we introduced extended Annotation Graphs (eAG), a cyclic-graph data model equipped with a novel schema mechanism that, by allowing validation "by construction", bypasses the typical algorithmic cost of traditional methods for the validation of graph-structured data. We introduce here LeAG, a markup syntax for eAG annotations over text data. LeAG takes the shape of a classic, inline markup model. A LeAG annotation can then be written, in a human-readable form, in any notepad application, and saved as a text file; the syntax is simple and familiar -- yet LeAG proposes a natural syntax for multilayer annotation with (self-) overlap and links. From a theoretical point of view, LeAG inaugurates a hybrid markup paradigm. Syntactically speaking, it is a full inline model, since the tags are all inserted along the annotated resources; still, we evidence that representing independent elements' co-occurring in an inline manner requires to make the annotation rest upon a notion of reference value, that is typical of stand-off markup. To our knowledge, LeAG is the first inline markup syntax to properly conceptualize the notion of elements' accidental co-occurring, that is yet fundamental in multilevel annotation.