The SDM data model is the interface that tells the SDM
engine how to get the data to be displayed. The SDM data model is
an abstract description of a set of nodes and links between nodes.
Nodes and links have a user-defined type (also called the “tag”),
and a set of named properties.
JViews Diagrammer provides prebuilt data models,
and you can implement the data model interface to connect your data.