Form features, like protrusions or depressions on a face, through-holes or handles, can be extracted from a relational boundary model of a solid object, called the ‘symmetric boundary graph’ by loop identification and connected component labelling. The result is a decomposition of the object boundary into volumetric components describing features, which is represented as a directed labelled multigraph, called the ‘object decomposition graph’. Based on such a model, issues such as representation uniqueness and matching of object descriptions are discussed.