The Marble Framework has got two major design goals:
The KML standard itself describes the properties of a data model for maps:
GeoData holds the data model that is internally used for any geographic information which should be rendered. It deals whith the data only, drawing is performed elsewhere.
GeoDataDocument describes a document.
A model representation is built through parsing of files and creating a stack of GeoDataObject representing its data. The Geodata objects are all modeled after the Google KML files as defined in the KML documentation.