This paper constitutes a preliminary report on the work carried out on semantic content annotation in the LIRICS project, in close collaboration with the activities of ISO TC 37/SC 4/TDG 31. This consists primarily of: (1) identifying commonalities in alternative approaches to the annotation and representation of various types of semantic information; and (2) developing methodological principles and concepts for identifying and characterising representational concepts for semantic content. The LIRICS project does not aim to develop a standard format for the annotation and representation of semantic content, but at providing well-defined descriptive concepts. In particular, the aim is to build an on-line registry of definitions of such concepts, called data categories, in accordance with ISO standard 12620. These semantic data categories are abstract concepts, whose use is not restricted to any particular format or representation language. We advocate the use of the metamodel as a tool to extract the most important of these abstract overarching concepts, with examples from dialogue act, temporal, reference and semantic role annotation.