Each of the types of item defined by the topic maps data model is represented in the TMCore API by an interface. The names of the interfaces may be slightly unfamiliar to users of the XTM syntax because they are based on a more abstract model of a topic map called the "Topic Maps Data Model" (TMDM). This model is currently under development as part of the next version of ISO 13250 and so the TMCore interfaces cover both this model and a slightly modified version of it for XTM 1.0 topic maps. For more information about TMDM see the ISO Topic Maps website.