A new hierarchical model for solid object representation is described. This model, called a hierarchical face adjacency hypergraph (HFAH), is based on a relational description of the object boundary, called a face adjacency hypergraph (FAH), which considers faces as the primary topological entities defining the object boundary. The HFAH consists of a hierarchy of FAHs describing the decomposition of the boundary of an object into form features. In this paper the HFAH is described together with its internal encoding structure. Two basic transformations, called refinement and abstraction, are defined on the hierarchical model; these allow effective and efficient modifications of the hierarchical boundary model.